HYDROGEN ENGINE OF WORKING GAS CIRCULATION TYPE

BACKGROUND OF THE INVENTION r

1. Field of the Invention

[0001] The present invention relates to a hydrogen engine of a working gas circulation type, in which oxygen, hydrogen that produces water vapor by combustion, and an inactive working gas (for example, a gas composed of a monoatomic molecules) having a specific heat ratio higher than that of water vapor are supplied into a combustion chamber, hydrogen as the fuel is combusted in the combustion chamber and the working gas is caused to expand, thereby producing a power, and the working gas contained in a gas after the combustion that has been discharged from the combustion chamber is again supplied into the combustion chamber.

2. Description of the Related Art

[0002] A hydrogen engine of a working gas circulation type in which oxygen, hydrogen, and argon gas as a working gas are supplied into a combustion chamber, the hydrogen is combusted, and the working gas contained in an exhaust gas discharged from the combustion chamber is circulated in the combustion chamber via a circulation channel has been suggested. Because the specific heat ratio of argon gas is higher than that of the air, the hydrogen engine using the argon gas as a working gas can be operated at a high heat efficiency.

[0003] Hydrogen burns and forms bonds with oxygen, water vapor is generated. Because the water vapor is a gas of molecules (triatomic molecules) composed of three atoms, the specific heat ratio thereof is lower than that of argon, which is a gas of molecules (monoatomic molecules) composed of one atom. Therefore, when the working gas contained in the exhaust gas discharged from the combustion chamber is circulated into the combustion chamber via the circulation channel, in order to maintain the heat efficiency of the engine at a high level, it is desirable to remove water vapor

contained in the gas that is circulated (can be referred to hereinbelow as "circulating gas"). Accordingly, in the conventional hydrogen engine, a condenser is provided in the circulation channel, water vapor contained in the circulating gas is liquefied, condensed and separated (removed) with the condenser, and the gas obtained by separating the water vapor converted into water of condensation from the circulating gas is again supplied into the combustion chamber (see, for example, Japanese Patent Application Publication No. 11-93681 (JP-A-11-93681)).

[0004] However, the condenser used in the conventional hydrogen engine is either of a water cooling type or an air cooling type, and water vapor is liquefied, condensed and separated by inducing heat exchange with the atmosphere. Therefore, even the lowest temperature of the exhaust gas is not as low as the atmospheric temperature. On the other hand, a saturated water vapor amount increases with the increase in gas temperature. Therefore, when the atmospheric temperature is high, the exhaust gas temperature does not decrease sufficiently and, as a consequence, the saturated water vapor amount of the exhaust gas is also high. As a result, water vapor cannot be sufficiently removed from the exhaust gas, the specific heat ratio of the circulating gas functioning as a working gas decreases and, therefore, the heat efficiency of the engine decreases.

SUMMARY OF THE INVENTION [0005] A hydrogen engine of a working gas circulation type according to a first aspect of the present invention is a hydrogen engine of a working gas circulation type, in which oxygen, hydrogen as a fuel, and an inactive working gas having a specific heat ratio higher than that of water vapor are supplied into a combustion chamber, the fuel is combusted in the combustion chamber and the working gas is caused to expand, thereby producing a power, and the working gas contained in a gas after the combustion that has been discharged from the combustion chamber is again supplied into the combustion chamber. The hydrogen engine of a working gas circulation type according to the first aspect includes: a circulation channel which links an exhaust port communicating with the combustion chamber to an intake port communicating with the combustion chamber

on the outside of the combustion chamber, wherein the working gas contained in the gas after combustion that has been discharged from the combustion chamber is again supplied into the combustion chamber via the circulation channel; a condenser, which is installed in the circulation channel, performs heat exchange of a gas, introduced from an inlet portion and flowing in the circulation channel, with an atmosphere, thereby condensing water vapor contained in the gas and producing water of condensation, and discharging from an outlet portion a gas obtained by separating water vapor that has been converted into water of condensation by the heat exchange from the gas; and a first moisture adsorption device, which is installed in the circulation channel downstream of the condenser in the gas flow direction, accommodates a hygroscopic material inside thereof, and, after water vapor contained in the gas introduced from an inlet portion has been adsorbed by the hygroscopic material, discharges the gas from an outlet portion into the circulation channel.

[0006] The circulation path includes first to fifth channel portions. [0007] The condenser performs heat exchange of a gas introduced from an inlet portion thereof (pre-condensation gas, pre-condensation circulating gas) with an atmosphere inside thereof, thereby condensing water vapor contained in the pre-condensation gas and producing water of condensation, and discharges from an inlet portion thereof a gas (post-condensation gas, post-condensation circulating gas, circulating gas after separation of water of condensation) obtained by separating "water vapor that has been converted into water of condensation by the heat exchange" from the pre-condensation gas. The first moisture adsorption device accommodates a hygroscopic material. After water vapor contained in the gas introduced from an inlet portion of the first moisture adsorption device has been adsorbed by the hygroscopic material, the first moisture adsorption device discharges the gas from an outlet portion.

[0008] The first channel portion forms a channel that links the exhaust port communicating with the combustion chamber to an inlet portion of the condenser. The second channel portion forms a channel that links an outlet portion of the condenser to a first connection point. The third channel portion forms a channel that links the first

connection point to an inlet portion of the first moisture adsorption device. The fourth channel portion forms a channel that links an outlet portion of the first moisture adsorption device to a second connection point. The fifth channel portion forms a channel that links the second connection point to the intake port communicating with the combustion chamber.

[0009] In this case, the second channel portion and third channel portion may be formed by mutually independent tubular members (pipes, ducts, etc.), or may be formed by one tubular member. Likewise, the fourth channel portion and fifth channel portion may be formed by mutually independent tubular members, or may be formed by one tubular member.

[0010] In this case, by causing combustion of hydrogen in the combustion chamber, a gas (pre-combustion circulating gas; at this time, it can be also called "exhaust gas") containing at least "water vapor and monoatomic molecular gas" is discharged into the first channel portion via the exhaust port. The circulating gas discharged into the first channel portion then flows from an inlet portion of the condenser into the condenser. Water vapor contained in the circulating gas that has flown into the condenser is condensed within a space from the inlet portion to the outlet portion of the condenser and separated from the circulating gas. The circulating gas (post-condensation circulating gas) from which water vapor has been separated is discharged from the outlet portion of the condenser into the second channel portion, then passes through the third channel portion and flows from an inlet portion of the first moisture adsorption device into the first moisture adsorption device. In this case, part of water vapor contained in the circulating gas (water vapor that has not been completely separated by condensation in the condenser and remains in the circulating gas) is adsorbed by the hygroscopic material contained in first moisture adsorption device and separated from the circulating gas. The circulating gas (circulating gas after adsorption of water vapor) that has flown out of an outlet portion of the first moisture adsorption device is supplied into the combustion chamber via the fourth channel portion, fifth channel portion, and intake port.

[0011] The water vapor contained in the circulating gas is thus separated from the

circulating gas not only with the condenser, but also with the first moisture adsorption device. Therefore, even when the atmospheric temperature is high and the water vapor contained in the circulating gas cannot be sufficiently separated and removed by the condenser, because the water vapor is also removed by the first moisture adsorption device, the concentration of water vapor (amount of water vapor) in the circulating gas supplied into the combustion chamber can be reduced. As a result, the average specific heat ratio of circulating gas (that is, the gas that essentially functions as a working gas) supplied into the combustion chamber can be maintained at a high level and, therefore, the heat efficiency of the engine can be maintained at a high level. [0012] The hydrogen engine of a working gas circulation type according to the first aspect may further include a connection channel portion that links the first connection point to the second connection point, and a first control valve that regulates a flow rate (Gl) of a gas flowing into the connection channel portion, this gas being part of a gas flowing into the first connection point via the second channel portion, and a flow rate (G2) of a gas flowing into the third channel portion, this gas being part of a gas flowing into the first connection point via the second channel portion.

[0013] In this case the amount (G2) of circulating gas passing through the first moisture adsorption device can be controlled by the first control valve. The "capacity to adsorb water vapor (water vapor adsorption ratio)" of the hygroscopic material of the first moisture adsorption device decreases as the hygroscopic material adsorbs water vapor. Therefore, where the hydrogen engine of a working gas circulation type is provided with the first control valve, for example, when the atmospheric temperature is low and water vapor contained in the circulating gas can be sufficiently separated and removed by the condenser, "the amount (G2) of circulating gas passing through the first moisture adsorption device is decreased (flow rate (Gl) of the gas flowing into the connection channel portion is increased) by using the first control valve, thereby making it possible to avoid unnecessary adsorption of water vapor by the hygroscopic material. As a result, rapid decrease in the moisture adsorption capacity of the hygroscopic material can be avoided.

[0014] The first control valve can be configured by two or more three-way valves (flow rate regulating valve, opening and closing valve, and the like). As an example of the first control valve, a three-way valve may be used that has one inlet portion and two outlet portions and discharges a gas introduced from the inlet portion to either one of the two outlet portions selected based on a direction signal. In this case, the first control valve (the three-way valve) may be disposed in the first connection point, the inlet portion of the first control valve may communicate with the second channel portion, one of the two outlet portions of the first control valve may communicate with the third channel portion, and the other of the two outlet portions of the first control valve may communicate with the connection channel portion.

[0015] With such a configuration, the amount (G2) of the circulating gas passing through the first moisture adsorption device can be easily controlled using one three-way valve.

[0016] Further, the hydrogen engine of a working gas circulation type that includes the above-described first control valve may further include water vapor amount acquisition means for acquiring a water vapor amount contained in a gas discharged from the outlet portion of the condenser into the second channel portion; and first control valve control means for controlling the first control valve so that when the acquired water vapor amount is large, a ratio (G2/G1) of an amount G2 of gas flowing into the third channel portion to an amount Gl of gas flowing into the connection channel portion increases over that when the acquired water vapor amount is small.

[0017] With such a configuration, when the water vapor contained in the circulating gas is not sufficiently removed by separation in the condenser due, for example, to a high atmospheric temperature, the ratio of the amount G2 of gas flowing into the third channel portion to the amount Gl of gas flowing into the connection channel portion increases. Therefore, extra water vapor contained in the circulating gas can be separated and removed with the first moisture adsorption device. In other words, when the water vapor contained in the circulating gas can be sufficiently separated and removed with the condenser due to a low atmospheric temperature, or the like, the amount (G2) of

circulating gas passing through the first moisture adsorption device decreases and the flow rate (Gl) of gas flowing into the connection channel portion increases. Therefore, unnecessary adsorption of water vapor by the hygroscopic material of the first moisture adsorption device can be avoided. As a result, rapid deterioration of moisture adsorption capacity of the hygroscopic material can be avoided.

[0018] However, hygroscopic materials such as silica gel typically have a property such that the capacity thereof to adsorb water vapor (water vapor adsorption ratio) decreases as the hygroscopic material adsorbs water vapor. Furthermore, the hygroscopic materials have a property such that the capacity thereof to adsorb water vapor (water vapor adsorption capacity) decreases dramatically when the temperature thereof is equal to or higher than a predetermined temperature. Thus, where a hygroscopic material is heated to a predetermined temperature (or to a temperature equal to or higher than a predetermined temperature), the adsorbed water vapor (moisture) is released (moisture is desorbed from the hygroscopic material). As a result, the moisture adsorption capacity of the hygroscopic material (moisture adsorption capacity when the temperature of the hygroscopic material decreased) is increased (restored).

[0019] Accordingly, the hydrogen engine of a working gas circulation type may include first moisture adsorption device regeneration means for heating the hygroscopic material accommodated in the first moisture adsorption device and desorbing moisture that has been adsorbed by the hygroscopic material from the hygroscopic material.

[0020] With such a configuration, the hygroscopic material is heated using the first moisture adsorption device regeneration means within an appropriate period (the hygroscopic material is heated so that the temperature of the hygroscopic material becomes equal to or higher than a predetermined temperature) and the water vapor (moisture) adsorbed by the hygroscopic material is released, thereby making it possible to increase (restore) the moisture adsorption capacity. Thus, the hygroscopic material can be regenerated. As a result, the hydrogen engine of a working gas circulation type can be operated with a high heat efficiency over a long period.

[0021] The first moisture adsorption device regeneration means may be "a first

s moisture adsorption device heating channel portion" that branches from the first channel portion in a branching point on the first channel portion, passes in the vicinity of the first moisture adsorption device, and merges with the first channel portion in a merging point on the first channel portion downstream of the branching point (on the downstream side in the flow direction of the circulating gas when the circulating gas flows in the first channel portion).

[0022] Here, the mode in which the first moisture adsorption device heating channel portion "passes in the vicinity of the first moisture adsorption device" includes a mode in which the first moisture adsorption device heating channel portion passes within a predetermined distance from the first moisture adsorption device, a mode in which the first moisture adsorption device heating channel portion passes in the vicinity of the first moisture adsorption device so as to encircle the first moisture adsorption device, and a mode in which a through space is formed inside the first moisture adsorption device, and a pipe (heart radiation pipe) forming the first moisture adsorption device heating channel portion is passed via the through space. In other words, the expression "the first moisture adsorption device heating channel portion passes in the vicinity of the first moisture adsorption device" means that "the first moisture adsorption device heating channel portion is installed so that the heat generated from the first moisture adsorption device heating channel portion can heat the first moisture adsorption device (hygroscopic material of the first moisture adsorption device)."

[0023] With such a configuration, the gas discharged from the combustion chamber passes from the first channel portion via the branching point and through the first moisture adsorption device heating channel portion and then returns via the merging point to the first channel portion and flows into the condenser. Because the gas discharged from' combustion chamber has a high temperature, the first moisture adsorption device heating channel portion assumes a high temperature. Therefore, the first moisture adsorption device heating channel portion can heat and regenerate the first moisture adsorption device (hygroscopic material of the first moisture adsorption device) located in the vicinity of this device heating channel portion. Thus, with such an aspect,

exhaust gas at a high temperature that is discharged from the hydrogen engine of a working gas circulation type can be used as a heat source for heating and regenerating the "hygroscopic material of the first moisture adsorption device ".

[0024] When the hydrogen engine of a working gas circulation type has the first moisture adsorption device heating channel portion, as described hereinabove, the hydrogen engine of a working gas circulation type may include "a second control valve" that regulates a ratio (G4/G3) of "a flow rate G4 of gas flowing in the first moisture adsorption device heating channel portion" to "a flow rate G3 of gas flowing in the first channel portion between the branching point and the merging point". [0025] With such a configuration, by using the second control valve, it is possible to increase the flow rate G4 of the gas, thereby regenerating the hygroscopic material accommodated in the first moisture adsorption device, when a desired condition is established. Further, when it is not necessary to regenerate the hygroscopic material accommodated in the first moisture adsorption device, the control can be performed such that the circulating gas is "caused to pass only through the first channel portion, without passing through the first moisture adsorption device heating channel portion". As a result, a back pressure (exhaust gas pressure) of the engine and/or a pressure loss occurring during circulation of the circulating gas can be decreased and, therefore, the hydrogen engine of a working gas circulation type can be operated at a higher efficiency. [0026] Further, the hydrogen engine of a working gas circulation type including the second control valve may include hygroscopic material regeneration condition determination means for determining whether a hygroscopic material regeneration condition under which the hygroscopic material is regenerated by desorbing moisture that has been adsorbed by the hygroscopic material of the first moisture adsorption device from the hygroscopic material is met; and means for path control during regeneration for controlling the second control valve so that the entire gas discharged from the exhaust port flows in the first moisture adsorption device heating channel portion and that the gas discharged from the exhaust port does not flow between the branching point and merging point of the first channel portion when the hygroscopic material regeneration condition is

determined to be met, and for controlling the second control valve so that the entire gas discharged from the exhaust port flows between the branching point and merging point of the first channel portion and the gas discharged from the exhaust port does not flow in the first moisture adsorption device heating channel portion when the hygroscopic material regeneration condition is determined not to be met.

[0027] With such a configuration, when the hygroscopic material regeneration condition is determined to be established, the entire gas discharged from the exhaust port flows in the first moisture adsorption device heating channel portion. Therefore, when the hygroscopic material regeneration condition is determined to be established, the hygroscopic material of the first moisture adsorption device is regenerated with good efficiency (moisture that has been adsorbed by the hygroscopic material is desorbed from the hygroscopic material with good efficiency).

[0028] Furthermore, the means for path control during regeneration may be configured to control the first control valve so that the entire gas flowing in the second channel portion, when the hygroscopic material regeneration condition is determined to be met, flows in the connection channel portion.

[0029] With such a configuration, because the gas that has passed through the condenser does not pass through "the first moisture adsorption device in which the adsorbed moisture is being desorbed by heating" when the hygroscopic material regeneration condition is determined to be met, the concentration of water vapor in the circulating gas does not increase and, at the same time, the hygroscopic material of the first moisture adsorption device can release moisture with good efficiency.

[0030] In addition, the means for path control during regeneration may be configured to control the first control valve so that the entire gas flowing in the second channel portion flows in the third channel portion when the hygroscopic material regeneration condition is determined not to be met.

[0031] With such a configuration, when the hygroscopic material regeneration condition is determined to be met, the entire gas flowing in the second channel portion can pass through "the first moisture adsorption device in which the adsorbed moisture is

not being desorbed by heating". Therefore, the concentration of water vapor in the circulating gas can be efficiently reduced.

[0032] Further, in this case, an example of the hygroscopic material regeneration condition is a condition such that "the amount of water vapor contained in the gas discharged from the outlet portion of the condenser into the second channel portion" that has been acquired by the water vapor acquisition means is equal to or less than a predetermined value. Where the hygroscopic material regeneration conditions is thus established, when "the amount of water vapor contained in the gas discharged from the outlet portion of the condenser into the second channel portion" is larger than the predetermined value, a large amount of circulating gas can be caused to flow into the first moisture adsorption device via the third channel portion by the first control valve. In this case, the gas discharged from the combustion chamber is prohibited by the second control valve from passing through the first moisture adsorption device heating channel portion. As a result, when the amount of water vapor in the circulating gas is larger, the amount of water vapor in the circulating gas can be reduced with good efficiency by the condenser and the first moisture adsorption device. On the other hand, when "the amount of water vapor contained in the gas discharged from the outlet portion of the condenser into the second channel portion" is less than the predetermined value, the circulating gas is prevented by the first control valve from flowing into the first moisture adsorption device. In this case, the gas discharged from the combustion chamber is allowed by the second control valve to pass through the first moisture adsorption device heating channel portion. As a result, the hygroscopic material can be regenerated with good efficiency.

[0033] One special technical feature of the hydrogen engine of a working gas circulation type according to the aspect of the present invention is that the engine includes a condenser and a first moisture adsorption device in a circulation channel (alternatively, the first moisture adsorption device is installed downstream of the condenser in the circulation channel portion). Therefore, according to another aspect of the hydrogen engine of a working gas circulation type in accordance with the present

invention, a condenser, a first moisture adsorption device, and a second moisture adsorption device may be provided. Similarly to the first moisture adsorption device, second moisture adsorption device accommodates a hygroscopic material and, after water vapor contained in the gas introduced from an inlet portion has been adsorbed by the hygroscopic material, the second moisture adsorption device discharges the gas from an outlet portion.

[0034] In this case, the hydrogen engine of a working gas circulation type may further include a sixth channel portion that links an exhaust port communicating with the combustion chamber to a first branching point; a seventh channel portion configuring a first circulating gas path that starts from the first branching point, passes in the vicinity of the first moisture adsorption device, then passes through the inlet portion and the outlet portion of the condenser (that is, reaches the inlet portion of the condenser and passes through the condenser and then passes through the outlet portion of the condenser), then passes through the inlet portion and the outlet portion of the second moisture adsorption device (that is, reaches the inlet portion of the second moisture adsorption device and passes through the second moisture adsorption device and then passes through the outlet portion of the second moisture adsorption device), and then reaches an intake port communicating with the combustion chamber; an eighth channel portion configuring a second circulating gas path that starts from the first branching point, passes in the vicinity of the second moisture adsorption device, then passes through the inlet portion and the outlet portion of the condenser (that is, reaches the inlet portion of the condenser and passes through the condenser and then passes through the outlet portion of the condenser), then passes through the inlet portion and the outlet portion of the first moisture adsorption device (that is, reaches the inlet portion of the first moisture adsorption device and passes through the first moisture adsorption device and then passes through the outlet portion of the first moisture adsorption device), and then reaches an intake port; and circulating gas channel portion selection means for selecting either the seventh channel portion or the eighth channel portion and re-supplying a working gas contained in a gas after combustion that has been discharged from the combustion chamber into the combustion

chamber via the selected channel portion. In this case, the internal portions of the condenser, first moisture adsorption device, and second moisture adsorption device configure parts of the selected channel portion.

[0035] With such a configuration, one channel portion from among the seventh channel portion and the eighth channel portion is selectively selected, for example, alternately for each elapsed predetermined interval. Where the seventh channel portion is selected, the hygroscopic material of the first moisture adsorption device is regenerated and the separation and removal of water vapor from the circulating gas is performed by the condenser and the second moisture adsorption device. Where the eight channel portion is selected, the hygroscopic material of the second moisture adsorption device is regenerated and the separation and removal of water vapor from the circulating gas is performed by the condenser and the first moisture adsorption device. Therefore, the hygroscopic material of the first moisture adsorption device and the hygroscopic material of the second moisture adsorption device are constantly maintained in a state in which they can adsorb water vapor at a high water vapor adsorption capacity (high water vapor adsorption ratio). Further, the water vapor contained in the circulating gas is constantly separated and removed from the circulating gas by the condenser and either one of the first moisture adsorption device and the second moisture adsorption device. As a result, the water vapor contained in the circulating gas can be separated and removed with good efficiency over a long period (the concentration of water vapor in the circulating gas supplied into the combustion chamber is maintained at a low value with good stability over a long period). In addition, the frequency of replacing the hygroscopic materials of the first and second moisture adsorption devices can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The features, advantages, and technical and industrial significance of this invention will be described in the following detailed description of example embodiments of the invention with reference to the accompanying drawings, in which like numerals denote like elements, and wherein:

FIG 1 is a schematic diagram of a hydrogen engine of a working gas circulation type of a first example of the present invention;

FIG 2 is a flowchart illustrating a routine executed by a central processing unit (CPU) of the electric control unit shown in FIG 1; FIG 3 is a flowchart illustrating a routine executed by the CPU of the electric control unit shown in FIG 1;

FIG 4 is a flowchart illustrating a routine executed by the CPU of the electric control unit shown in FIG 1;

FIG 5 is a graph showing how a theoretical heat efficiency of the engine, specific heat ratio of gas, steam separation ratio, and saturated water vapor pressure vary depending on a circulating gas temperature;

FIG 6 is a schematic diagram of a hydrogen engine of a working gas circulation type of a second example of the present invention;

FIG 7 is a schematic diagram illustrating a modification example of a first moisture adsorption device shown in FIG 6;

FIG 8 is a flowchart illustrating a routine executed by the CPU of the hydrogen engine of a working gas circulation type of the second example of the present invention;

FIG 9 is a schematic diagram of a hydrogen engine of a working gas circulation type of a third example of the present invention; and FIG 10 is a flowchart illustrating a routine executed by the CPU of the hydrogen engine of a working gas circulation type of the third example of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

[0037] The examples of the hydrogen engine of a working gas circulation type in accordance with the present invention will be described below with reference to the appended drawings. The hydrogen engine of a working gas circulation type of the examples is a four-cycle multi-cylinder engine in which "oxygen (oxygen gas)" and "argon that is a working gas" are supplied into a combustion chamber, hydrogen (hydrogen gas) serving as "a fuel that generates water vapor on combustion (bonding

with oxygen)" is injected into a gas under a high pressure obtained by compressing the aforementioned gases, and this hydrogen is diffusion combusted. Further, the hydrogen engine of a working gas circulation type of the examples is also an engine of a working gas circulation type in which the working gas contained in the exhaust gas discharged from the combustion chamber via an exhaust port is circulated (re-supplied) into the combustion chamber via a circulation channel portion (circulation channel, circulation path) and an intake port.

[0038] The working gas used in the hydrogen engine of a working gas circulation type of the examples may be "an inactive gas with a specific heat ratio higher than that of water vapor". Therefore, the working gas is not limited to argon gas and may be a gas (inactive gas) composed of monoatomic molecules other than argon, for example, helium (He), and an inactive gas composed of diatomic molecules such as nitrogen gas. The present examples can be also applied to an engine of a system in which an ignition plug is provided in a combustion chamber and hydrogen is spark ignited and combusted by an ignition spark generated from the ignition plug.

[0039] <First Example> FIG 1 is a schematic diagram of a hydrogen engine 10 of a working gas circulation type of the first example of the present invention. The engine 10 includes a hydrogen supply portion 40, an oxygen supply portion 50, a working gas circulation channel portion 60, a condenser 80, a first moisture adsorption device 90, and an electronic control unit 100. FIG 1 shows a cross section of a specific cylinder of the engine 10 and cross sections of an intake port and an exhaust port connected to the specific cylinder, and other cylinders have the same configuration. In the explanation below, a gas circulating from the exhaust port into the intake port via the working gas circulation channel portion 60 will be also called "circulating gas". [0040] The engine 10 is an engine of a piston reciprocation type including a cylinder head 11 in which a cylinder head portion is formed, a cylinder 12 in which a cylinder block portion is formed, a piston 13 reciprocating inside the cylinder 12, a crankshaft 14, a connecting rod 15, which connects the piston 13 and the crankshaft 14 and converts the reciprocating movement of the piston 13 into the rotary movement of the crankshaft 14,

and an oil pan 16 connected to the cylinder block. A piston ring 13a is installed on the side surface of the piston 13.

[0041] A space formed by the cylinder head 11, cylinder 12, and oil pan 16 is divided by the piston 13 into a combustion chamber 21 on the top surface side of the piston 13 and a crankcase 22 accommodating the crankshaft 14.

[0042] An intake port 31 communicating with the combustion chamber 21 and an exhaust port 32 communicating with the combustion chamber 21 are formed in the cylinder head 11.

[0043] An intake valve 33 for opening and closing the intake port 31 is installed in the intake port 31. An intake valve drive mechanism composed of an intake camshaft and the like (not shown in the figure) is installed in the cylinder head 11. The intake valve drive mechanism opens and closes the intake valve 33, thereby opening and closing the intake port 31.

[0044] An exhaust valve 34 for opening and closing the exhaust port 32 is installed in the exhaust port 32. An exhaust valve drive mechanism composed of an exhaust camshaft or the like (not shown in the figure) is installed in the cylinder head 11. The exhaust valve drive mechanism opens and closes the exhaust valve 34, thereby opening and closing the exhaust port 32.

[0045] Further, a hydrogen injection valve 35 that directly inject hydrogen (hydrogen gas) into the combustion chamber 21 (into the cylinder) is installed in the cylinder head

11. When the hydrogen injection valve 35 is opened in response to a drive signal

(injection direction signal), the hydrogen gas is directly injected into the combustion chamber 21.

[0046] The hydrogen supply portion 40 includes a hydrogen tank (hydrogen gas tank, hydrogen cylinder) 41, a hydrogen gas channel 42, a hydrogen gas pressure regulator 43, a hydrogen gas flowmeter 44, and a surge tank 45.

[0047] The hydrogen tank 41 is a gas fuel storage tank that stores a hydrogen gas serving as a fuel in a high-pressure state. The hydrogen gas channel 42 is a channel (pipe) that links the hydrogen tank 41 to the hydrogen injection valve 35. A hydrogen

gas pressure regulator 43, hydrogen gas flowmeter 44, and surge tank 45 are installed in the hydrogen gas channel 42 in the order of description from the hydrogen tank 41 to the hydrogen injection valve 35.

[0048] The hydrogen gas pressure regulator 43 is a well-known pressure regulator. The hydrogen gas pressure regulator 43 decreases the pressure of hydrogen gas within the hydrogen tank 41 and regulates the pressure inside the hydrogen gas channel 42 downstream (side of the surge tank 45) of the hydrogen gas pressure regulator 43 to a predetermined pressure.

[0049] The hydrogen gas flowmeter 44 measures the amount of hydrogen gas (hydrogen gas flow rate) flowing in the hydrogen gas channel 42 and generates a signal FH2 representing the hydrogen gas flow rate. The surge tank 45 reduces pulsations generated within the hydrogen gas channel 42 when the hydrogen gas is injected.

[0050] The oxygen supply portion 50 includes an oxygen tank (oxygen gas tank, oxygen cylinder) 51, an oxygen gas channel 52, an oxygen gas pressure regulator 53, an oxygen gas flowmeter 54, and an oxygen gas mixer 55.

[0051] The oxygen tank 51 stores an oxygen gas at a predetermined pressure. The oxygen gas channel 52 is a channel (pipe) linking the oxygen tank 51 to the oxygen gas mixer 55. The oxygen gas pressure regulator 53 and oxygen gas flowmeter 54 are installed in the oxygen gas channel 52 in the order of description from the oxygen tank 51 to the oxygen gas mixer 55.

[0052] The oxygen gas pressure regulator 53 is a well-known pressure regulator of a variable regulated pressure type. Thus, the oxygen gas pressure regulator 53 can regulate the pressure within the oxygen gas channel 52 downstream (side of the oxygen gas mixer 55) of the oxygen gas pressure regulator 53 to a target regulated pressure R02tgt corresponding to a direction signal. In other words, the oxygen gas pressure regulator 53 can control the oxygen gas amount flowing in the oxygen gas channel 52 in response to the direction signal.

[0053] The oxygen gas flowmeter 54 measures the amount (oxygen gas flow rate) of oxygen gas flowing in the oxygen gas channel 52 and generates a signal representing the

oxygen gas flow rate F02. The oxygen gas mixture 55 is installed in a fifth channel portion 65 of the below-described working gas circulation channel portion 60. The oxygen gas mixer 55 mixes the oxygen supplied via the oxygen gas channel 52 and a circulation gas (mainly, argon gas that is a working gas) supplied to an inlet portion 55a of the oxygen mixer 55 via the fifth channel portion 65 and discharges the mixed gases from an outlet portion 55b into the fifth channel portion 65.

[0054] The working gas circulation channel portion 60 includes first to fifth channel portions (first to fifth paths, first to fifth flow path forming tubes) 61 to 65, a connection channel portion 66, a first control valve (three-way valve) 67, a first opening and closing valve 68, a desorbed moisture discharge path 69, and a second opening and closing valve 71. The first to fifth channel portions, connection channel portion 66, and desorbed moisture discharge path 69 are formed by tubular members (pipes, ducts, etc.).

[0055] The first channel portion 61 forms a channel that links the exhaust port 32 communicating with the combustion chamber 21 to an inlet portion 80a of the condenser 80. The second channel portion 62 forms a channel that links an outlet portion 80b of the condenser 80 to a first connection point Cl. The third channel portion 63 forms a channel that links the first connection point Cl to an inlet portion 90a of a first moisture adsorption device 90.

[0056] The fourth channel portion 64 forms a channel that links an outlet portion 90b of the first moisture adsorption device 90 to a second connection point C2. The fifth channel portion 65 forms a channel that links the second connection point C2 to the intake port 31 communicating with the combustion chamber 21. The connection channel portion 66 forms a channel that links the first connection point Cl to the second connection point C2. [0057] The first control valve 67 is provided in the first connection point Cl. The first control valve 67 is a flow rate control valve that can regulate a flow rate Gl of "a gas flowing into the connection channel portion 66" from among "gases flowing into the first connection point Cl via the second channel portion 62" and a flow rate G2 of "a gas flowing into the third channel portion 63" from among "gases flowing into the first

connection point Cl via the second channel portion 62". Thus, the first control valve 67 can change a ratio (G2/G1) of "an amount G2 of gas flowing into the third channel portion 63" to "an amount Gl of gas flowing into the connection channel portion 66" in response to a direction signal. [0058] More specifically, the first control valve 67 is a three-way valve (path switching valve) that has one inlet portion and two outlet portions and can discharge a gas introduced from the inlet portion from "any one from among the two outlet portions" selected based on a direction signal. The inlet portion of the first control valve 67 communicates with the second channel portion 62. Thus, the inlet portion of the first control valve 67 communicates with the outlet portion 80b of the condenser 80 via the second channel portion 62.

[0059] "One of the two outlet portions" of the first control valve 67 communicates with the third channel portion 63. Thus, "one of the two outlet portions" of the first control valve 67 communicates with the inlet portion 90a of the first moisture adsorption device 90 via the third channel portion 63. "The other of the two outlet portions" of the first control valve 67 communicates with the connection channel portion 66. Thus, "the other of the two outlet portions" of the first control valve 67 communicates with the second connection point C2 via the connection channel portion 66.

[0060] Actually, the first control valve 67 is configured so as to supply selectively the entire circulating gas flowing in the second channel portion 62 only to either of the third channel portion 63 and connection channel portion 66 in response to a direction signal. Thus, the first control valve 67 can set the aforementioned ratio (G2/G1) of gas flow rates to 0 or an infinitely large amount.

[0061] The first opening and closing valve 68 is installed (inserted) in the fourth channel portion 64. The first opening and closing valve 68 selectively attains either a state in which the fourth channel portion 64 is closed (closed state, through flow inhibition state) or a state in which the fourth channel portion 64 is open (open state, through flow permitted state).

[0062] The desorbed moisture discharge path 69 is connected by one end thereof to a

connection point C3 on the fourth channel portion 64 and opened at the other end thereof to an atmosphere. The connection point C3 is positioned between the outlet portion 90b of the first moisture adsorption device 90 and the first opening and closing valve 68 on the fourth channel portion 64. [0063] The second opening and closing valve 71 is installed (inserted) in the desorbed moisture discharge path 69. The second opening and closing valve 71 selectively attains either a state in which the desorbed moisture discharge path 69 is closed (closed state, through flow inhibition state) or a state in which the desorbed moisture discharge path 69 is open (open state, through flow permitted state). [0064] The crankcase 22 and fifth channel portion 65 are connected by a blow-by gas return channel BR. The blow-by gas return channel BR is installed so that the blow-by gas that leaked into the crankcase 22 returns to the fifth channel portion 65.

[0065] The condenser 80 induces inside thereof heat exchange between a gas (pre-condensation gas) introduced from the inlet portion 80a thereof and atmosphere via cooling water, thereby condensing water vapor contained in the pre-condensation gas, and discharges a gas (post-condensation gas) obtained by separating "water vapor converted into water of condensation by the heat exchange" from the pre-condensation gas from the outlet portion 80b thereof.

[0066] The first moisture adsorption device 90 accommodates a hygroscopic material (for example, silica gel). The hygroscopic material has a property such that the capacity thereof to adsorb water vapor (water vapor adsorption ratio) decreases as the water vapor is adsorbed. Furthermore, the hygroscopic material also has a property such that the capacity thereof to adsorb water vapor decreases significantly when the temperature thereof becomes equal to or higher than a predetermined temperature. Thus, where the hygroscopic material is heated to a temperature equal to or higher than a predetermined temperature, the adsorbed water vapor (moisture) is released (moisture is desorbed from the hygroscopic material). As a result, where the hygroscopic material temperature is raised to a temperature equal to or higher than the predetermined temperature and then lowered below it, the moisture adsorption capacity of the

hygroscopic material increases (is restored). In the first moisture adsorption device 90, water vapor contained in the gas introduced from the inlet portion 90a of the device is adsorbed by the hygroscopic material and separated (removed), and the gas (circulating gas after water vapor adsorption) from which the water vapor has been separated (removed) is discharged from the outlet portion 90b.

[0067] The electric control unit 100 is an electronic device that has as a main component a well-known microcomputer including a CPU, a read only memory (ROM), an random access memory (RAM), a nonvolatile memory, and an interface. The hydrogen gas flowmeter 44, the oxygen gas flowmeter 54, an accelerator pedal operation amount sensor 101, an engine revolution speed sensor (crank angle sensor) 102, and a circulating gas temperature sensor 103 are connected to the electric control unit 100. The electric control unit 100 inputs measurement signals (detection signals) from these devices.

[0068] The accelerator pedal operation amount sensor 101 detects the operation amount of an accelerator pedal AP and outputs a signal Accp representing the operation amount of the accelerator pedal AP. The engine revolution speed sensor 102 generates a signal NE representing an engine revolution speed and a signal representing a crank angle based on the revolution speed of the crankshaft 14.

[0069] The circulating gas temperature sensor 103 detects the temperature of the "circulating gas after separation of water of condensation (post-condensation gas)", which is the circulating gas flowing through the installation site (second channel portion 62), and generates a signal Tex representing the gas temperature. The circulating gas after separation of water of condensation is a circulating gas after the water vapor condensed with the condenser 80 has been separated. [0070] The electric control unit 100 is also connected to the hydrogen injection valve

35 of each cylinder, oxygen gas pressure regulator 53, first control valve 67, first opening and closing valve 68, and second opening closing valve 71 and sends direction signals or drive signals thereto.

[0071] The operation of the hydrogen engine 10 of a working gas circulation type

that has the above-described configuration will be described below with reference to FIGS. 2 to 4.

[0072] The CPU of the electric control unit 100 executes an injection control routine shown by a flowchart in FIG 2 each time the crank angle of the engine 10 matches a predetermined crank angle (for example, a crank angle of 10° before a compression upper dead center of each cylinder). Therefore, where the crank angle of the engine 10 matches the predetermined crank angle, the CPU starts the processing of this routine from step 200, advances to step 205, and finds a required hydrogen amount SH2 based on "an accelerator pedal operation amount Accp (load) detected at the present time and an engine revolution speed NE detected at the present time" and "a function fl". The function fl is a function for finding "the required hydrogen amount SH2" necessary to generate "an operation required torque" determined by the "accelerator pedal operation amount Accp and engine revolution speed NE". The function fl is determined empirically in advance and stored in the ROM, for example, in the form of a lookup table. Therefore, where hydrogen in the required hydrogen amount SH2 determined by the function fl is diffusion combusted, the engine 10 generates a torque substantially equal to the operation required torque.

[0073] Then, the CPU advances to step 210 and converts the required hydrogen amount SH2 into a hydrogen injection timing TAU, which is the valve opening timing of the hydrogen injection valve 35, based on the required hydrogen amount SH2, engine revolution speed NE determined at the present time, and a function f2 (for example, a lookup table) established in advance. Then, the CPU advances to step 215, sends to the hydrogen injection valve 35 "a drive signal" that opens the hydrogen injection valve 35 of a cylinder for which the crack angle is a crank angle 10° before the compression upper dead center at the hydrogen injection timing TAU, advances to step 295, and completes the present routine. As a result, hydrogen in an amount necessary to generate the required torque is supplied into the combustion chamber 21 and combusted by diffusion combustion.

[0074] The CPU may also determine a hydrogen gas injection timing (gas fuel

injection timing) based on the accelerator pedal operation amount Accp (load) detected at the present time and the engine revolution speed NE detected at the present time and inject the hydrogen gas at this hydrogen gas injection timing. In any case, the hydrogen gas injection timing is a timing close to the compression upper dead center and is set to a timing at which the diffusion combustion is performed with good stability.

[0075] The CPU then executes a regulator control routine shown by a flowchart in FIG 3 for each predetermined elapsed interval. Therefore, at a predetermined timing, the CPU starts the processing of this routine from step 300, advances to step 305, and calculates an average value SH2ave per unit time of the required hydrogen amount SH2 at the present time. This calculation is performed by integrating the entire required hydrogen amount SH2 relating to each cylinder, which is found in the above-described step 205 shown in FIG 2, over a unit time. Then, the CPU advances to step 310 and finds, a target oxygen gas flow rate F02tgt based on the average SH2ave found in the above-described manner and a function f3 (for example, lookup table) established in advance.

[0076] The engine 10 causes combustion of hydrogen as a fuel. Therefore, in order to generate only water by hydrogen combustion, 1 mol of oxygen (oxygen gas) has to be supplied per 2 mol of hydrogen (hydrogen gas). For this purpose, the function f3 determines the target oxygen gas flow rate F02tgt so that the number of moles of oxygen that is half the number of moles of hydrogen represented by the average value SH2ave (actually, oxygen in an amount obtained by adding an appropriately large margin amount to the oxygen amount corresponding to the number of moles half that of the hydrogen) are supplied into the combustion chamber 21 per unit time.

[0077] The CPU then advances to step 315 and determines whether the oxygen gas flow rate F02 determined at the present time is equal to or higher than the target oxygen gas flow rate F02tgt. When the CPU determines that the oxygen gas flow rate F02 determined at the present time is equal to or higher than the target oxygen gas flow rate F02tgt, the CPU advances to step 320 and decreases a target regulated pressure R02tgt of the oxygen gas pressure regulator 53 by a positive constant value (a). As a result, the

amount of oxygen gas supplied to the oxygen gas mixer 55 decreases.

[0078] On the other hand, when the CPU determines in step 315 that the oxygen gas flow rate F02 determined at the present time is less than the target oxygen gas flow rate F02tgt, the CPU advances to step 325 and increases the target regulated pressure R02tgt of the oxygen gas pressure regulator 53 by a positive constant value (b). As a result, the amount of oxygen gas supplied to the oxygen gas mixer 55 increases. As a consequence, oxygen is supplied in a necessary and sufficient amount to the combustion chamber 21 via the oxygen gas mixer 55. The CPU then advances to step 395 and completes the present routine. As a result, the appropriate amounts of hydrogen gas and oxygen gas are supplied to the combustion chamber 21.

[0079] The CPU then executes a path control routine shown by a flowchart in FIG 4 for each predetermined elapsed interval. Therefore, at a predetermined timing, the CPU starts the processing of this routine from step 400, advances to step 405, and acquires a temperature Tex of the circulating gas after separation of water of condensation at the present time based on a signal from a circulating gas temperature sensor 103.

[0080] A curve C in FIG 5 shows a saturated water vapor pressure versus a temperature of circulating gas. It is assumed that when the temperature of circulating gas is 60 ⁰ C, water vapor at about 20 kPa is contained in the gas. In this case, a theoretical heat efficiency ηth of the engine vs. a temperature of circulating gas is represented by curves Ll to L4, a specific heat ratio K of gas versus a temperature of circulating gas is represented by curves Ml to M4, and a steam separation ratio versus a temperature of circulating gas is represented by curves Nl to N4. Here, the curves Ll, Ml, and Nl represent the case in which the water vapor is completed condensed and separated for each circulating gas temperature (saturated condensation), and the curves L2, M2, and N2 represent the case in which the water vapor is condensed and separated in an amount of 90% that during saturated condensation at the circulating gas temperature. Further, the curves L3, M3, and N3 represent the case in which the water vapor is condensed and separated in an amount of 50% that during saturated condensation at the circulating gas temperature, and the curves L4, M4, and N4 represent the case in which

the water vapor is condensed and separated in an amount of 20% that during saturated condensation at the circulating gas temperature.

[0081] FIG 5 shows that the specific heat ratio K of circulating gas (gas with the exception of oxygen supplied into the combustion chamber) increases with the decrease in the circulating gas temperature and increase in the steam separation ratio. As a result, in can be assumed that the theoretical heat efficiency ηth of the engine also rises. The theoretical heat efficiency ηth of the engine can be found from the following Equation (1), where e stands for a compression ratio of the engine. ηth = l - (l/ε ^{κ l} ) ... l [0082] As described above, the smaller is the amount of water vapor contained in the gas supplied into the combustion chamber 21, the higher is the heat efficiency (the better is the efficiency) at which the engine 10 can operate.

[0083] Accordingly, the CPU advances to step 410 and acquires a saturated water vapor amount PH2O at the present time based on the "temperature Tex of the circulating gas after separation of water of condensation" that was acquired in step 405 and a function f4. The function f4 is, as the curve C in FIG 5 shows, "a function established in advance" that represents a relationship between the "temperature Tex of the circulating gas after separation of water of condensation" and saturated water vapor amount PH2O.

[0084] The CPU then advances to step 415 and determines whether the saturated water vapor amount PH2O acquired in step 410 is larger than a predetermined value (path switching determination value) PH2Oth.

[0085] Let us assume that the saturated water vapor amount PH2O acquired in step 410 is smaller than a predetermined value PH2Oth. In this case, the amount of water vapor contained in the circulating gas after separation of water of condensation is comparatively small. Therefore the engine 10 can operate at a comparatively high heat efficiency even when the water vapor contained in the circulating gas is not removed by separation using the first moisture adsorption device 90.

[0086] Accordingly, the CPU determines "No" in step 415, advances to step 420, and sends a direction signal to the first control valve 67 so as to link the second channel

portion 62 and the connection channel portion 66. Thus, the CPU sends to the first control valve 67 a direction signal instructing the first control valve to link the inlet portion thereof to that outlet portion from among the two outlet portions that is connected to the connection channel portion 66. [0087] Then, the CPU advances to step 425, closes (blocks) the fist opening and closing valve 68, and opens (releases) the second opening and closing valve 71 in step 430. The CPU then advances to step 495 and completes the present routine.

[0088] As a result, the entire circulating gas (circulating gas after separation of water of condensation) flowing in the second channel portion 62 flows from the second channel portion 62 into the connection channel portion 66, and this circulating gas is thereafter supplied into the combustion chamber 21 via the fifth channel portion 65 and intake port 31. Thus, because the circulating gas does not pass through the first moisture adsorption device 90, the adsorption of water vapor (moisture adsorption) using the hygroscopic material of the first moisture adsorption device 90 is stopped. Therefore, because the hygroscopic material of the first moisture adsorption device 90 does not adsorb the water vapor unnecessarily, rapid decrease in the moisture adsorption capacity of the hygroscopic material can be avoided. Furthermore, the first moisture adsorption device 90 is opened to the atmosphere via part of the fourth channel portion 64 and the desorbed moisture discharge path 69. As a result, the moisture adsorbed by the hygroscopic material of the first moisture adsorption device 90 is gradually desorbed from the hygroscopic material and released to the atmosphere.

[0089] Let us now assume, that the saturated water vapor amount PH2O acquired in step 410 is larger than a predetermined value PH2Oth. In this case, the amount of water vapor contained in the circulating gas after separation of water of condensation is comparatively large. Therefore, the amount of water vapor contained in the circulating gas becomes too high unless the water vapor is further separated and removed by the first moisture adsorption device 90. As a result, the average specific heat ratio of the gas (circulating gas supplied into the combustion chamber 21) that functions as a working gas becomes too small and, therefore, the heat efficiency of the engine 10 decreases.

[0090] Accordingly, in this case, the CPU determines "Yes" in step 415, advances to step 435, and sends a direction signal to the first control valve 67 such as to link the second channel portion 62 and third channel portion 63. Thus, the CPU sends to the first control valve 67 a direction signal instructing the first control valve to link "the inlet portion thereof and "the outlet portion from among the two outlet portions that is connected to the third channel portion 63". Then, the CPU advances to step 440, opens (releases) the first opening and closing valve 68, and then closes (blocks) the second opening and closing valve 71 in step 445. The CPU then advances to step 495 and completes the present routine. [0091] As a result, the circulating gas discharged from the combustion chamber 21 initially flows into the condenser 80 through the first channel portion 61. Therefore, the water vapor contained in the circulating gas is condensed as the circulating gas moves "from the inlet portion 80a to the outlet portion 80b of the condenser 80" and separated from the circulating gas. The circulating gas from which the water vapor has been separated is discharged from the outlet portion 80b of the condenser 80 into the second channel portion 62 and then flows from the inlet portion 90a of the first moisture adsorption device 90 into the first moisture adsorption device 90 via the third channel portion 63. Then, part of the water vapor remaining in the circulating gas (water vapor that is not completely separated by condensation in the condenser 80 and remains in the circulating gas) is adsorbed by the hygroscopic material retained in the first moisture adsorption device 90 and separated from the circulating gas. The circulating gas flowing out of the outlet portion 90b of the first moisture adsorption device 90 is then supplied into the combustion chamber 21 via the fourth channel portion 64, fifth channel portion 65, and intake port 31. [0092] Thus, the water vapor contained in the circulating gas is separated from the circulating gas not only with the condenser 80, but also with the first moisture adsorption device 90. Therefore, even when the atmospheric temperature is high and the water vapor contained in the circulating gas is not sufficiently removed by separation with the condenser 80 (the saturated water vapor pressure is high), because the water vapor is also

removed by the first moisture adsorption device 90, the concentration of water vapor in the circulating gas supplied into the combustion chamber 21 can be reduced. Therefore, the average specific heat ratio of the circulating gas supplied into the combustion chamber 21 (that is, the gas that functions as a working gas) can be maintained at a high value. As a result, the heat efficiency of the engine 10 can be maintained at a high value.

[0093] As described hereinabove, in the engine 10 of the first example of the present invention, when the saturated water vapor amount PH2O is higher than the predetermined value PH2Oth, that is, when the amount of water vapor contained in the circulating gas passing through the condenser 80 is higher than a predetermined value, the amount of water vapor contained in the circulating gas can be decreased using the first moisture adsorption device 90 provided downstream of the condenser 80 in the flow direction of the circulating gas. Therefore, because the amount of water vapor contained in the circulating gas re-supplied into the combustion chamber 21 can be reduced, the specific heat capacity of the gas functioning as a working gas is not substantially increased. As a result, the engine 10 can continuously operate at a high efficiency.

[0094] Further, when the saturated water vapor amount PH2O is lower than the predetermined value PH2Oth (that is, when the atmospheric temperature is low and the water vapor contained in the circulating gas is sufficiently separated and removed by the condenser 80, thereby making it unnecessary to use the first moisture adsorption device 90), the engine 10 performs control such that the circulating gas does not pass through the first moisture adsorption device 90. Therefore, unnecessary adsorption of the water vapor by the hygroscopic material accommodated in the first moisture adsorption device 90 can be avoided. As a result, rapid decrease in the moisture adsorption capacity of the hygroscopic material can be avoided.

[0095] The first control valve 67 is a three-way valve that functions as a path switching valve, but this valve can be also configured so that by regulating a ratio (T1/T2) of a time Tl in which the inlet portion of the valve communicates with one outlet portion (outlet portion connected to the third channel portion 63) from among the two

outlet portions to a time T2 in which the inlet portion communicates with another outlet portion (outlet portion connected to the connection channel portion 66) of the two outlet portions, the ratio (G2/G1) of "a flow rate (G2) of gas flowing into the third channel portion 63, this gas being part of the gas flowing into the first connection point Cl via the second channel portion 62" to "a flow rate (Gl) of gas flowing into the connection portion 66, this gas being part of the gas flowing into the first connection point Cl via the second channel portion 62" will be adjusted to any value. In this case, the CPU controls the ratio (T1/T2) so that the ratio (G2/G1) of the gas flow rate G2 to the gas flow rate Gl increases with the increase in the above-described acquired saturated water vapor amount PH2O (see step 410 in FIG 4). In this case, the ratio (G2/G1) can be increased with the increase of the ratio (T1/T2).

[0096] With such a configuration, the amount (G2) of circulating gas passing through the first moisture adsorption device 90 can be controlled with good accuracy by the first control valve 67. As a result, "the capacity to adsorb water vapor (water vapor adsorption ratio)" of the hygroscopic material of the first moisture adsorption device 90 can be controlled with good accuracy to a high value, and the amount of water vapor contained in the circulating gas re-supplied to the combustion chamber 21 can be controlled with good accuracy.

[0097] <Second Example> The engine of the second example of the present invention differs from the engine of the above-described first example in including a first moisture adsorption device heating channel portion 72 and a second control valve 73, as shown in FIG 6. Accordingly, the explanation below will be focused on this difference between the engines of the two examples.

[0098] The first moisture adsorption device heating channel portion 72 is composed of a metal pipe with good heat radiation ability. The first moisture adsorption device heating channel portion 72 is a channel portion that branches from the first channel portion 61 in a branching point Dl located on the first channel portion 61 and merges with the first channel portion 61 in a merging point D2 located on the first channel portion 61. The merging point D2 is positioned downstream of the branching point Dl

in the direction of the circulating gas flow in the first channel portion 61. The first moisture adsorption device heating channel portion 72 passes in the vicinity of the first moisture adsorption device 90. In the present specification, the expression "the first moisture adsorption device heating channel portion 72 passes in the vicinity of the first moisture adsorption device 90" means that the "first moisture adsorption device heating channel portion 72 is installed so that the heat generated by the first moisture adsorption device heating channel portion 72 can heat the first moisture adsorption device 90 (hygroscopic material located inside the first moisture adsorption device 90) (so that the temperature of the hygroscopic material can be raised to a predetermined temperature or a higher temperature) " .

[0099] Therefore, the first moisture adsorption device heating channel portion 72 may: (1) pass through within a through space 90c provided inside the first moisture adsorption device 90, as shown in FIG 6, or (2) be disposed so as to encircle the first moisture adsorption device 90, as shown in FIG. 7, or (3) simply pass through in the vicinity of the first moisture adsorption device 90.

[0100] The second control valve 73 is disposed at the branching point Dl. The second control valve 73 is a flow rate control valve that can regulate a ratio (G4/G3) of "a flow rate G4 of gas flowing in the first moisture adsorption device heating channel portion 72" to "a flow rate G3 of gas flowing in the main circulation channel between the branching point Dl and the merging point D2"

[0101] More specifically, the second control valve 73 is a three-way valve (flow path switching valve) that has one inlet portion and two outlet portions and can discharge a gas introduced from the intake portion from "either of the two outlet portions" selected based on a direction signal. The outlet portion of the second control valve 73 communicates with "an upstream portion of the first channel portion 61" linking the branching point Dl and exhaust port 32.

[0102] "One of the two outlet portions" of the second control valve 73 communicates with "a downstream portion of the first channel portion 61" linking the branching point Dl to the merging point D2 (therefore, the inlet portion 80a of the condenser 80). Thus,

"one of the two outlet portions" of the second control valve 73 communicates with the merging point D2 via the downstream portion of the first channel portion 61. "The other of the two outlet portions" of the second control valve 73 communicates with the first moisture adsorption device heating channel portion 72. Thus, "the other of the two outlet portions" of the second control valve 73 communicates with the merging point D2 via the first moisture adsorption device heating channel portion 72.

[0103] The second control valve 73 is configured so that the entire circulating gas discharged via the exhaust port 32 into the first channel portion 61 is selectively supplied to either one of "the first channel portion 61 downstream of the branching point Dl (downstream portion of the first channel portion 61)" and "the first moisture adsorption device heating channel portion 72" in response to a direction signal. Therefore, the second control valve 73 can set the ratio (G4/G3) of gas flow rates either to 0 or to an infinitely large value.

[0104] The CPU of the electric control unit 100 of the hydrogen engine 10 of a working gas circulation type of the second example that is configured in the above-described manner executes the routines shown in FIGS. 2 and 3. This CPU also executes a path control routine shown by a flowchart in FIG 8 replacing FIG 4 of the first example. The operation based on the routines shown in FIGS. 2 and 3 has already been explained. Therefore, the operation of CPU will be explained below with reference to FIG 8. From among the steps shown in FIG 8, those identical to the steps shown in FIG 4 are assigned with reference numeral identical to those of the steps shown in FIG 4 and the detailed explanation thereof is omitted.

[0105] The CPU executes the path control routine shown in FIG 8 for each predetermined interval. Therefore, the CPU starts the processing of this routine at a predetermined timing from step 800 and executes the processing of step 405 and step 410, thereby acquiring a saturated water vapor amount PH2O at the present time. Then, the CPU advances to step 415 and determines whether the saturated water vapor amount PH2O acquired in the step 410 is larger than a predetermined value (path switching determination value) PH2Oth.

[0106] In this case, where the saturated water vapor amount PH2O acquired in the step 410 is smaller than the predetermined value PH20th, the amount of water vapor contained in the circulating gas immediately after it has been discharged from the condenser 80 (circulating gas after separation of water of condensation) is comparatively small. Therefore, even when the water vapor contained in the circulating gas is not removed by the separation using the first moisture adsorption device 90, the average specific heat ratio of the gas functioning as a working gas (circulating gas supplied into the combustion chamber 21) is maintained at a large value, thereby enabling the engine 10 to operate at a comparative high heat efficiency. [0107] Accordingly, the CPU determines "No" in step 415, advances to step 420, sends a direction signal to the first control valve 67, and links the second channel portion 62 to the connection channel portion 66. Thus, the CPU sends a connection channel portion selection signal that selects the connection channel portion 66 to the first control valve 67. As a result, the entire circulating gas flowing in the second channel portion 62 (circulating gas after separation of water of condensation) flows from the second channel portion 62 into the connection channel portion 66 and is then supplied into the combustion chamber 21 via the fifth channel portion 65 and the intake port 31. Thus, because the circulating gas does not pass through the first moisture adsorption device 90, the adsorption of water vapor (moisture adsorption) using the hygroscopic material of the first moisture adsorption device 90 is stopped. Therefore, the hygroscopic material of the first moisture adsorption device 90 does not adsorb the water vapor unnecessarily. As a result, a rapid decrease in the moisture adsorption capacity of the hygroscopic material can be avoided.

[0108] The CPU then advances to step 805 and sends a direction signal to the second control valve 73 so as to link "a portion of the first channel portion 61 upstream of the branching point Dl (upstream portion of the first channel portion 61)" to "the first moisture adsorption device heating channel portion 72". Thus, the CPU sends to the second control valve 73 a direction signal (first moisture adsorption device heating channel portion selection signal for selecting the first moisture adsorption device heating

channel portion 72) that causes the linking of the inlet portion to, from among the two outlet portions, the outlet portion that is "connected to the first moisture adsorption device heating channel portion 72". Then, the CPU advances to step 425, closes (blocks) the first opening and closing valve 68, and opens (releases) the second opening and closing valve 71 in step 430. Then, the CPU advances to step 895 and completes the present routine.

[0109] As a result, "the high-temperature exhaust gas (high-temperature pre-condensation gas)" discharged via the discharge port 32 passes through the first moisture adsorption device heating channel portion 72 and then flows into the condenser 80. Therefore, the first moisture adsorption device heating channel portion 72 passing in the vicinity (the internal through space 90c in FIG 6) of the first moisture adsorption device 90 is heated by the high-temperature exhaust gas and generates heat. As a result, the first moisture adsorption device heating channel portion 72 heats the hygroscopic material accommodated in the first moisture adsorption device 90. Therefore, the temperature of the hygroscopic material accommodated in the first moisture adsorption device rises and the hygroscopic material releases the adsorbed moisture (water vapor that has heretofore been adsorbed). Thus, the moisture is desorbed from the hygroscopic material. The desorbed moisture is then released to the atmosphere via part of the fourth channel portion 64, desorbed moisture exhaust path 69, and the second opening and closing valve 71. As a result, the water vapor adsorption ratio of the hygroscopic material attained when the temperature decreases is increased. Thus, the hygroscopic material is regenerated.

[0110] On the other hand, when the saturated water vapor amount PH2O acquired in step 410 is larger than the predetermined value PH2Oth, the amount of water vapor contained in the circulating gas after separation of water of condensation is comparatively large. Therefore, the amount of water vapor contained in the circulating gas becomes excessively large unless the water vapor is further separated and removed with the first moisture adsorption device 90. As a result, the average specific heat ratio of the gas functioning as a working gas (circulating gas supplied into the combustion chamber 21)

becomes too low and, therefore, the heat efficiency of the engine 10 decreases.

[0111] Accordingly, in this case, the CPU determines "Yes" in step 415, advances to step 435, and sends a direction signal to the first control valve 67 such as to link the second channel portion 62 and third channel portion 63. Thus, the CPU sends to the first control valve 67 a direction signal (third channel portion selection signal that selects the third channel portion) that causes the valve to link "the inlet portion thereof to "the outlet portion from among the two outlet portions that is connected to the third channel portion 63".

[0112] The CPU then advances to step 810 and sends to the second control valve 73 a direction signal such as to link "a portion of the first channel portion 61 located upstream of the branching point Dl (upstream portion of the first channel portion 61)" to "a portion of the first channel portion 61 located downstream of the branching point Dl (downstream portion of the first channel portion 61)". Thus, the CPU sends to the second control valve 73 a direction signal (first channel portion selection signal that selects a channel portion on the downstream side of the first channel portion 61) that causes the valve to link "the inlet portion thereof to "an outlet portion connected to a portion of the first channel portion 61 located upstream of the branching point Dl". Then, the CPU advances to step 440, opens (releases) the first opening and closing valve 68, and closes the second opening and closing valve 71 in step 445. The CPU then advances to step 895 and completes the present routine.

[0113] As a result, the water vapor contained in the circulating gas discharged from the combustion chamber 21 passes from the branching point Dl through the downstream side of the first channel portion 61 and is directly introduced from the inlet portion 80a of the condenser 80 into the condenser 80, without passing through the first moisture adsorption device heating channel portion 72. Then, this water vapor contained in the circulating gas is condensed while moving from the inlet portion 80a to the outlet portion 80b of the condenser 80 and separated from the circulating gas. The circulating gas from which the water vapor has been separated passes from the outlet portion 80b of the condenser 80 through the second channel portion 62 and third channel portion 63 and is

introduced from the inlet portion 90a of the first moisture adsorption device 90 into the first moisture adsorption device 90. Part of the water vapor contained in the circulating gas (water vapor that has not been completely separated by condensation in the condenser 80 and remains in the circulating gas) is then adsorbed by the hygroscopic material retained in the first moisture adsorption device 90 and separated from the circulating gas. In this case, the hygroscopic material of the first moisture adsorption device 90 is not heated by the first moisture adsorption device heating channel portion 72, and because the hygroscopic material has been restored in the preceding appropriate period, the water vapor is adsorbed with good efficiency. The circulating gas flowing out of the outlet portion 90b of the first moisture adsorption device 90 is supplied into the combustion chamber 21 via the fourth channel portion 64, fifth channel portion 65, and intake port 31.

[0114] As described hereinabove, the engine 10 of the second example of the present invention demonstrates an effect identical to that of the engine of the first example. In addition, the engine 10 of the second example includes first moisture adsorption device regeneration means (first moisture adsorption device heating channel portion 72) for heating the hygroscopic material accommodated in the first moisture adsorption device 90 and desorbing the moisture that has been adsorbed by the hygroscopic material from the hygroscopic material. Therefore, it is possible to heat the hygroscopic material by using the first moisture adsorption device regeneration means within an appropriate period (for example, within a period in which the removal of water vapor using the first moisture adsorption device 90 is unnecessary, such as a period in which the saturated water vapor amount PH2O of the circulating gas that passed through the condenser 80 is less than the predetermined value PH2Oth) and the moisture adsorption capacity of the hygroscopic material can be increased (restored). Thus, the hygroscopic material can be regenerated. As a result, the hydrogen engine 10 of a working gas circulation type can be operated with a high heat efficiency over a long interval, without frequent replacement of the hygroscopic material.

[0115] Furthermore, because the first moisture adsorption device heating channel

portion 72 is provided as the first moisture adsorption device regeneration means, the high-temperature exhaust gas discharged from the hydrogen engine 10 of a working gas circulation type can be used as a heat source for heating and regenerating "the hygroscopic material of the first moisture adsorption device 90". Thus, the energy generated by the engine 10 can be used with good efficiency to regenerate the hygroscopic material.

[0116] Further, the engine of the second example also includes hygroscopic material regeneration condition determination means (see step 415 in FIG 8) for determining whether "a hygroscopic material regeneration condition" under which the hygroscopic material is regenerated by desorbing moisture that has been adsorbed by the hygroscopic material of the first moisture adsorption device 90 from the hygroscopic material is realized, and means for path control during regeneration (see routine shown in FIG 8, in particular step 805 and step 810) for controlling the second control valve 73 so that the entire gas discharged from the exhaust port 32 flows in the first moisture adsorption device heating channel portion 72 and that the gas discharged from the exhaust port does not flow "between the branching point Dl and merging point D2 of the first channel portion 61" when the hygroscopic material regeneration condition is determined to be realized, and for controlling the second control valve 73 so that the entire gas discharged from the exhaust port 32 flows "between the branching point Dl and merging point D2 of the first channel portion 61" and the gas discharged from the exhaust port 32 does not flow in the first moisture adsorption device heating channel portion 72 when the hygroscopic material regeneration condition is determined not to be realized.

[0117] Accordingly, when the hygroscopic material regeneration condition is determined to be realized, the entire gas discharged from the exhaust port 32 flows in the first moisture adsorption device heating channel portion 72. Therefore, when the hygroscopic material regeneration condition is realized, the hygroscopic material of the first moisture adsorption device 90 is regenerated with good efficiency.

[0118] Further, the means for path control during regeneration (see routine shown in FIG 8) is configured so that when the hygroscopic material regeneration condition is

determined to be realized, the first control valve 67 is controlled so that the entire gas flowing in the second channel portion 62 flows in the connection channel portion 66, and when the hygroscopic material regeneration condition is determined not to be realized, the first control valve 67 is controlled so that the entire gas flowing in the second channel portion 62 flows in the third channel portion 63 (in particular, see step 420 to step 445 in FIG 8).

[0119] Therefore, when the hygroscopic material regeneration condition is determined to be realized, the gas including the remaining water vapor that has passed through the condenser 80 does not pass through "the first moisture adsorption device 90 in which the moisture that has heretofore been adsorbed is being desorbed from the hygroscopic material by heating with the first moisture adsorption device heating channel portion 72". Therefore, "the concentration of water vapor in the circulating gas that has decreased due to passage through the condenser 80" can be prevented by "the passage of the circulating gas through the first moisture adsorption device 90" from increasing again and, at the same time, the hygroscopic material of the first moisture adsorption device 90 can release moisture with good efficiency.

[0120] Further, when the hygroscopic material regeneration condition is determined not to be realized, the entire gas flowing in the second channel portion 62 can pass through "the first moisture adsorption device 90 in which the adsorbed moisture is not being desorbed by heating with the first moisture adsorption device heating channel portion 72". Therefore, the concentration of water vapor in the circulating gas can be decreased with good efficiency.

[0121] Further, in the second example, the hygroscopic material regeneration condition is realized when "the amount of water vapor contained in the gas discharged from the outlet portion 80b of the condenser 80 into the second channel portion 62" is equal to or less than a predetermined value. Therefore, when "the amount of water vapor contained in the gas discharged from the outlet portion 80b of the condenser 80 into the second channel portion 62" is larger than a predetermined value, the first control valve 67 can cause a large amount of circulating gas to flow into the first moisture

adsorption device 90 via the third channel portion 63. In this case, the second control valve 73 does not allow the exhaust gas discharged from the combustion chamber 21 to pass through the first moisture adsorption device heating channel portion 72. As a result, when the amount of water vapor in the circulating gas is large, the amount of water vapor in the circulating gas can be reduced with good efficiency.

[0122] On the other hand, when "the amount of water vapor contained in the gas discharged from the outlet portion 80b of the condenser 80 into the second channel portion 62" is equal to or less than a predetermined value, the first control valve 67 does not allow the circulating gas to flow into the first moisture adsorption device 90. In this case, the second control valve 73 allows the entire exhaust gas discharged from the combustion chamber 21 to flow through the first moisture adsorption device heating channel portion 72. As a result, the hygroscopic material of the first moisture adsorption device 90 can be regenerated with good efficiency.

[0123] In the second example, the first control valve 67 and second control valve 73 are switched at the same time. By contrast, when it is necessary to remove moisture from the circulating gas with the first moisture adsorption device 90 (for example, when "the amount of water vapor contained in the gas discharged from the outlet portion 80b of the condenser 80 into the second channel portion 62" is larger than a predetermined value), the second channel portion 62 and third channel portion 63 may be linked by the first control valve 67, and the upstream side of the first channel portion 61 and the downstream side portion of the first channel portion 61 may be linked by the second control valve 73. On the other hand, when it is not necessary to remove moisture from the first circulating gas with the 90, the second channel portion 62 and the connection channel portion 66 may be linked by the first control valve 67, and the upstream side of the first channel portion 61 and the downstream side portion of the first channel portion 61 may be linked by the second control valve 73. Further, the upstream side portion of the first channel portion 61 and the first moisture adsorption device heating channel portion 72 may be linked by the second control valve 73 only when the second channel portion 62 and connection channel portion 66 are linked by the first control valve 67 and

another condition (for example, a condition such that "an interval equal to or longer than a predetermined interval has passed" from the previous hygroscopic material regeneration execution event, or such that "the total integral revolution speed of the engine 10 became equal to or higher than a predetermined revolution speed") is realized. Thus, the "hygroscopic material regeneration condition" of the first moisture adsorption device 90 can be also set as a condition obtained by adding the "another condition" to a condition that "moisture adsorption execution condition" for the hygroscopic material of the first moisture adsorption device 90 is not realized.

[0124] Further, the second control valve 73 is a path switching valve, but it can be also so configured as to regulate the ratio (G4/G3) of "a flow rate G4 of gas flowing in the first moisture adsorption device heating channel portion 72" to "a flow rate G3 of gas flowing in the first channel portion 61 between the branching point Dl and the merging point D2" by regulating a ratio (T3/T4) of the time T3 in which the inlet portion of the valve is linked to either of the two outlet portions thereof to time T4 in which the inlet portion of the valve is linked to the other of the two outlet portions. In this case, the CPU controls the ratio (T3/T4) so that the ratio (G4/G3) of the gas flow rate G4 to the gas flow rate G3 increases with the decrease in the aforementioned acquired saturated water vapor amount PH2O.

[0125] Further, an electric heater that heats the first moisture adsorption device 90 (hygroscopic material accommodated in the first moisture adsorption device 90) may be provided as the first moisture adsorption device regeneration means instead of the first moisture adsorption device heating channel portion 72 or in addition to the first moisture adsorption device heating channel portion 72, and the hygroscopic material may be regenerated by switching on the electric heater when the hygroscopic material regeneration condition is realized.

[0126] <Third Examplo The hydrogen engine of a working gas circulation type of the third example of the present invention differs from the engine 10 of the first example mainly in including two moisture adsorption devices (that is, a first moisture adsorption device 90 and a second moisture adsorption device 95) as shown in FIG 9 and including

a working gas circulation channel portion 110 advantageous for these moisture adsorption devices. Accordingly, the explanation below will be focused on this difference.

[0127] As described above, the engine of the third example includes the first moisture adsorption device 90 and second moisture adsorption device 95. The second moisture adsorption device 95 is a moisture adsorption device that has a structure and functions identical to those of the first moisture adsorption device 90 explained in the first and second examples. Thus, the second moisture adsorption device 95 accommodates a hygroscopic material identical to the hygroscopic material (for example, silica gel) accommodated in the first moisture adsorption device 90. In the second moisture adsorption device 95, water vapor contained in the gas introduced from an inlet portion 95a of the second moisture adsorption device is adsorbed by the hygroscopic material, and the gas from which the water vapor has been removed by the adsorption on the hygroscopic material is discharged from an outlet portion 95b.

[0128] The working gas circulation channel portion 110 includes first to twelfth connection channel portions 111 to 122.

[0129] The first connection channel portion 111 links the exhaust port 32 communicating with the combustion chamber 21 to one inlet portion of a third control valve (third three-way valve) 73a provided in a first branching point El. The second connection channel portion 112 is composed of a metal pipe with good heat radiation ability. The second connection channel portion 112 links one of the two outlet portions of the third control valve 73a to a first merging point Fl. The second connection channel portion 112 passes in the vicinity of the first moisture adsorption device 90. Thus, the second connection channel portion 112 can heat the hygroscopic material of the first moisture adsorption device 90 when exhaust gas passes inside the second connection channel portion.

[0130] The third connection channel portion 113 links the first merging point Fl to the inlet portion 80a of the condenser 80. The fourth connection channel portion 114 links the outlet portion 80b of the condenser 80 and one inlet portion of a fourth control valve (fourth three-way valve) 74 provided in a second branching point E2. The fifth

connection channel portion 115 links one of the two outlet portions of the fourth control valve 74 to the inlet portion 90a of the first moisture adsorption device 90. The sixth connection channel portion 116 links the outlet portion 90b of the first moisture adsorption device 90 to one inlet portion of a fifth control valve (fifth three-way valve) 75 provided in a third branching point E3.

[0131] The seventh connection channel portion 117 links one of the two outlet portions of the fifth control valve 75 to the second merging point F2. The eighth connection channel portion 118 links the second merging point F2 to the intake port 31 of the combustion chamber 21. The ninth connection channel portion 119 is composed of a metal pipe with good heat radiation ability. The ninth connection channel portion 119 links the other of the two outlet portions of the third control valve 73a to the first merging point Fl. The ninth connection channel portion 119 passes in the vicinity of the second moisture adsorption device 95. Thus, the ninth connection channel portion 119 can heat the hygroscopic material of the second moisture adsorption device 95 when the exhaust gas passes inside the ninth connection channel portion.

[0132] The tenth connection channel portion 120 links the other of the two outlet portions of the fourth control valve 74 to the inlet portion 95a of the second moisture adsorption device 95. The eleventh connection channel portion 121 links the outlet portion 95b of the second moisture adsorption device 95 to one inlet portion of the sixth control valve (sixth three-way valve) 76 provided in the fourth branching point E4. The twelfth connection channel portion 122 links one of the two outlet portions of the sixth control valve 76 to the second merging point F2.

[0133] Further, the other of the two outlet portions of the fifth control valve 75 is connected to a channel open to the atmosphere. Likewise, the other of the two outlet portions of the sixth control valve 76 is connected to a channel open to the atmosphere.

[0134] The third control valve 73a, fourth control valve 74, fifth control valve 75, and sixth control valve 76 operate as shown in Table 1 below correspondingly to whether the operation is a first moisture adsorption device regeneration mode or a second moisture adsorption device regeneration mode. In the first moisture adsorption device

regeneration mode, the hygroscopic material of the first moisture adsorption device 90 is regenerated by heating, and the removal of water vapor contained in the circulating gas is performed with the condenser 80 and second moisture adsorption device 95. In the second moisture adsorption device regeneration mode, the hygroscopic material of the second moisture adsorption device 95 is regenerated by heating, and the removal of water vapor contained in the circulating gas is performed by the condenser 80 and first moisture adsorption device 90. Table 1

First moisture Third control Links the first connection channel portion 111 to the adsorption valve 73a second connection channel portion 112 device Disconnects the first connection channel portion 111 regeneration from the ninth connection channel portion 119 mode Fourth control Links the fourth connection channel portion 114 to valve 74 the tenth connection channel portion 120

Disconnects the fourth connection channel portion 114 from the fifth connection channel portion 115

Fifth control Opens the sixth connection channel portion 116 to valve 75 the atmosphere

Disconnects the sixth connection channel portion 116 from the seventh connection channel portion 117

Sixth control Links the eleventh connection channel portion 121 valve 76 to the twelfth connection channel portion 122

Stops the release of the eleventh connection channel portion 121 to the atmosphere

Second Third control Disconnects the first connection channel portion 111 moisture valve 73a from the second connection channel portion 112 adsorption Links the first connection channel portion 111 to the device ninth connection channel portion 119 regeneration Fourth control Disconnects the fourth connection channel portion mode valve 74 114 from the tenth connection channel portion 120

Links the fourth connection channel portion 114 to the fifth connection channel portion 115

Fifth control Stops the release of the sixth connection channel valve 75 portion 116 to the atmosphere

Links the sixth connection channel portion 116 to the seventh connection channel portion 117

Sixth control Disconnects the eleventh connection channel portion valve 76 121 from the twelfth connection channel portion 122 Opens the eleventh connection channel portion 121 to the atmosphere

[0135] As a result, the first to twelfth connection channel portions 111 to 122 configure sixth to eighth channel portions as described hereinbelow. Thus, the first

connection channel portion 111 configures the sixth channel portion linking the exhaust port 32 communicating with the combustion chamber 21 to the first branching point El.

[0136] The second connection channel portion 112, third connection channel portion 113, fourth connection channel portion 114, tenth connection channel portion 120, eleventh connection channel portion 121, twelfth connection channel portion 122, and eighth connection channel portion 118 configure "a seventh channel portion (first circulating gas path)", which starts from the first branching point El, passes in the vicinity of the first moisture adsorption device 90, then passes through the inlet portion 80a and outlet portion 80b of the condenser 80, then passes through the inlet portion 95a and outlet portion 95b of the second moisture adsorption device 95, and then reaches the intake port 31 communicating to the combustion chamber 21.

[0137] The ninth connection channel portion 119, third connection channel portion 113, fourth connection channel portion 114, fifth connection channel portion 115, sixth connection channel portion 116, seventh connection channel portion 117, and eighth connection channel portion 118 configure "an eighth channel portion (second circulating gas path)", which starts from the first branching point El, passes in the vicinity of the second moisture adsorption device 95, then passes through the inlet portion 80a and outlet portion 80b of the condenser 80, then passes through the inlet portion 90a and outlet portion 90b of the first moisture adsorption device 90, and then reaches the intake port 31 communicating to the combustion chamber 21.

[0138] In this case, when a certain path passes through the inlet portion 80a and outlet portion 80b of the condenser 80, as mentioned hereinabove, it means that this path configures a path that communicates with (reaches) the inlet portion 80a of the condenser 80, passes inside the condenser 80 to the outlet portion 80b, and starts from the outlet portion 80b to other portions. Likewise, when a certain path passes through the inlet portion 90a and outlet portion 90b of the first moisture adsorption device 90, as mentioned hereinabove, it means that this path configures a path that communicates with (reaches) the inlet portion 90a of the first moisture adsorption device 90, passes inside the first moisture adsorption device 90 to the outlet portion 90b, and starts from the outlet

portion 90b to other portions. Further, when a certain path passes through the inlet portion 95a and outlet portion 95b of the second moisture adsorption device 95, as mentioned hereinabove, it means that this path configures a path that communicates with (reaches) the inlet portion 95a of the second moisture adsorption device 95, passes inside the second moisture adsorption device 95 to the outlet portion 95b, and starts from the outlet portion 95b to other portions.

[0139] The CPU of the electric control unit 100 of the hydrogen engine 10 of a working gas circulation type of the third example having the above-described configuration executes the routines shown in FIGS. 2 and 3. Furthermore, this CPU also executes a path control routine shown by a flowchart in FIG 10 instead of that shown in FIG 4. The operation based on the routines shown in FIGS. 2 and 3 has already been explained. Therefore, the operation of the CPU will be explained below with reference to FIG 10.

[0140] The CPU executes the path control routine shown in FIG 10 for each predetermined elapsed interval. Therefore, the CPU starts the processing of the routine from step 1000 at a predetermined timing and increases the value of timer T by "1" in step 1005. Then, the CPU advances to step 1010 and determines whether the value of timer T is larger than a predetermined value Tth. In this case, if the value of timer T is not larger than the predetermined value Tth, the CPU determines "No" in step 1010, advances directly to step 1095, and completes the present routine.

[0141] The value of timer T is then increased over the predetermined value Tth repeating the processing of step 1005. In this case, the CPU advances to step 1010, determines "Yes" in the step 1010, advances to step 1015, and determines whether the value of a regeneration mode flag XM is "0". When the value of the regeneration mode flag XM is "1", such a flag indicates that the engine 10 operates in a first moisture adsorption device regeneration mode, and when this value is "0", the flag indicates that the engine 10 operates in the above-described second moisture adsorption device regeneration mode.

[0142] Assuming that the value of the regeneration mode flag XM is "0"

(regeneration of the hygroscopic material of the second moisture adsorption device 95 has been performed up to the present time), the CPU determines "Yes" in step 1015, advances to step 1020, and controls the third control valve 73a and fourth to sixth control valves 74 to 76 according to "the first moisture adsorption device regeneration mode shown in Table 1" so as to execute the first moisture adsorption device regeneration mode. Then, the CPU advances to step 1025 and sets the value of the regeneration mode flag XM to "1". The CPU then advances to step 1030, sets the value of timer T to "0", advances to step 1095, and completes the present routine.

[0143] As a result, because the circulating gas passes through the above-described "first circulating gas path (seventh channel portion)", the hygroscopic material of the first moisture adsorption device 90 is regenerated and the water vapor contained in the circulating gas is removed from the circulating gas in the condenser 80 and second moisture adsorption device 95.

[0144] Where the first moisture adsorption device regeneration mode continues for a predetermined time, the processing of step 1005 is repeated, so that the value of timer T again becomes higher than the predetermined value Tth. In this case, when the CPU advances to step 1010, it determines "Yes" in the step 1010, advances to step 1015 and determines whether the value of regeneration mode flag XM is "0". In this case, the value of the regeneration mode flag XM is "1" (that is, the regeneration of the hygroscopic material of the first moisture adsorption device 90 has been performed up to the present time). Therefore, the CPU determines "No" in step 1015, advances to step 1035, and controls the third control valve 73a and fourth to sixth control valves 74 to 76 as indicated in "the second moisture adsorption device regeneration mode shown in Table 1" so as to execute the second moisture adsorption device regeneration mode. Then, the CPU advances to step 1040, sets the value of regeneration mode flag XM to "0", advances to step 1030, sets the value of timer T to "0", advances to step 1095, and completes the present routine.

[0145] As a result, because the circulating gas passes through the above-described "second circulating gas path (eighth channel portion)", the hygroscopic material of the

second moisture adsorption device 95 is regenerated and the water vapor contained in the circulating gas is removed from the circulating gas in the condenser 80 and first moisture adsorption device 90.

[0146] Thus, in the hydrogen engine of a working gas circulation type of the third example, one channel portion from among the seventh channel portion and the eighth channel portion is selectively selected alternately for the elapsed predetermined interval. Therefore, the hygroscopic material of the first moisture adsorption device 90 and the hygroscopic material of the second moisture adsorption device 95 are maintained at all times in a state in which water vapor can be adsorbed at a high water vapor adsorption ratio, and the water vapor contained in the circulating gas is separated and removed at all times from the circulating gas with the condenser 80 and any one from among the first moisture adsorption device 90 and second moisture adsorption device 95. As a result, the water vapor contained in the circulating gas can be separated and removed with a high efficiency over a long interval (the concentration of water vapor in the circulating gas supplied into the combustion chamber 21 is maintained at a low value with good stability over a long interval). Furthermore, the frequency at which the hygroscopic material of the first moisture adsorption device 90 and second moisture adsorption device 95 has to be replaced can be reduced.

[0147] Further, in the third example, the condition for alternately and selectively selecting and switching the seventh channel portion and the eighth channel portion is that the engine operation time after the execution of the previous channel portion selection (switching) is "equal to or longer that a predetermined time (the value of timer T reaches the predetermined value Tth)", but this condition also may be that "the total integral revolution speed of the engine 10" after the execution of the previous channel portion selection (switching) is equal to or higher than a predetermined revolution speed", or that "the integral distance traveled by a vehicle carrying the engine 10" after the execution of the previous channel portion selection (switching) is equal to or longer than a predetermined distance.

[0148] As described hereinabove, with the hydrogen engines of a working gas

circulation type of the examples of the present invention, when the amount of water vapor contained in the circulating gas is still comparatively large despite the separation of the water vapor contained in the circulating gas from the circulating gas in the condenser 80, the water vapor contained in the circulating gas can be further separated from the circulating gas with the hygroscopic material of a moisture adsorption device (first moisture adsorption device 90 or second moisture adsorption device 95). Therefore, the average specific heat ratio of the circulating gas (gas essentially functioning as the working gas) supplied into the combustion chamber 21 can be maintained at a high value. As a result, the hydrogen engines of a working gas circulation type can be operated at a high heat efficiency.

[0149] The present invention is not limited to the above-described examples and various modification examples can be employed within the scope of the present invention. For example, the engines of the above-described examples employed diffusion combustion of hydrogen, but the present invention can be also employed in engines performing a natural ignition and combustion operation or a spark ignition combustion operation (flame propagation combustion) based on a spark from an ignition plug installed in the combustion chamber 21.

[0150] Further, the condenser 80 is of a water cooling type, but it may also be of an air cooling type. [0151] In the first example and second example, when the saturated water vapor amount PH2O exceeds the predetermined value PH2Oth, it is considered as "a water vapor additional removal execution condition (moisture adsorption execution condition) for additionally executing the removal of water vapor with the first moisture adsorption device 90", but the water vapor addition removal execution conditions can be also' set to any of the below-described conditions. Moreover, the above-described "hygroscopic material regeneration condition" also can be set to any of the below-described conditions.

[0152] (1) An atmospheric temperature is acquired with an atmospheric temperature sensor, and the aforementioned condition is realized when the atmospheric temperature is equal to or higher than a predetermined value. (2) When a predetermined interval

elapses after the removal of water vapor over a predetermined continuous interval by the first moisture adsorption device 90. (3) an internal pressure sensor is provided for determining a pressure inside the combustion chamber 21, an indicated torque of the hydrogen engine of a working gas circulation type is calculated based on the output from the internal pressure sensor and a crank angle (actually, the volume of combustion chamber 21 determined by the crank angle) acquired from an engine rotation speed sensor 102, the engine efficiency is acquired from the indicated torque and the charged amount of hydrogen, and the aforementioned condition is realized when the engine efficiency is equal to or less than a predetermined value. [0153] Water vapor amount acquisition means (for example, a water vapor amount sensor or a water vapor pressure sensor) that directly acquires the amount or concentration of water vapor contained in the circulating gas may be also used in place of the circulating gas temperature sensor 103. Furthermore, the hydrogen engines of a working gas circulation type of the above-described examples can be also referred to as engines of the below-described aspects.

[0154] <Aspect A> A hydrogen engine of a working gas circulation type, which has a circulation channel that links an exhaust port communicating with a combustion chamber to an intake port communicating with the combustion chamber on the outside of the combustion chamber, an in which a working gas contained in a gas after combustion that has been discharged from the combustion chamber is again supplied into the combustion chamber via the circulation channel, the engine including: a condenser 80 that is installed in the circulation channel, performs heat exchange of a circulating gas that is a gas introduced from an inlet portion and flowing in the circulation channel with an atmosphere, thereby condensing water vapor contained in the gas and producing water of condensation, and discharging from an inlet portion a circulating gas obtained by separating water vapor that has been converted into water of condensation by the heat exchange from the circulating gas; and a first moisture adsorption device 90 that is installed in the circulation channel downstream of the condenser in the circulating gas flow direction, accommodates a hygroscopic material inside thereof, and discharges the

circulating gas from an outlet portion into the circulation channel after water vapor contained in the circulating gas introduced from an inlet portion has been adsorbed by the hygroscopic material.

[0155] <Aspect B> The hydrogen engine of a working gas circulation type according to Aspect A, wherein the circulation channel includes a main circulation channel (61, 62, 66, 65) that links an exhaust port 32 to an intake port 31 and has the condenser 80 installed therein and a bypass channel (63, 64) that branches from the main circulation channel in a branching point (connection point Cl) on the main circulation channel downstream of the condenser in the circulating gas flow direction, merges with the main circulation channel in a merging point (connection point C2) on the main circulation channel downstream of the branching point in the circulating gas flow direction, and has the first moisture adsorption device 90 installed therein, and the engine further includes a first control valve 67 (flow path switching valve that can set and select a channel of the circulating gas flowing between the branching point and the merging point to either the main circulation channel and the bypass channel) that regulates a flow rate of the gas flowing into the bypass channel.

[0156] <Aspect C> The hydrogen engine of a working gas circulation type according to Aspect B, wherein the first control valve 67 is a three-way valve that selectively discharges a gas introduced from an inlet portion to either of two outlet portions selected in response to a direction signal, one inlet portion of the first control valve communicates with the outlet portion 80b of the condenser via the main circulation channel, one of the two outlet portions of the first control valve communicates with the inlet portion 90a of the first moisture adsorption device via the bypass channel, and the other of the two outlet portions of the first control valve communicates with the merging point (C2) via the main circulation channel (connection channel portion 66).

[0157] <Aspect D> The hydrogen engine of a working gas circulation type according to Aspect C, wherein means (first path switching means) for controlling the first control valve 67 is provided so that the entire circulating gas discharged into the main circulation channel via the outlet portion of the condenser flows through the bypass channel when a

water vapor amount in a circulating gas discharged from the condenser is determined to be larger than a predetermined value.

[0158] <Aspect E> The hydrogen engine of a working gas circulation type according to Aspects A to D, wherein hygroscopic material regeneration means (72) is provided for desorbing moisture from the hygroscopic material accommodated in the first moisture adsorption device by heating the hygroscopic material.

[0159] <Aspect F> The hydrogen engine of a working gas circulation type according to Aspect E, wherein the hygroscopic material regeneration means is a bypass channel 72 for heating that branches from a branching point of the main circulation channel between the exhaust port and the inlet portion of the condenser, then passes in the vicinity of the first moisture adsorption device, and merges with the main circulation channel in a merging point downstream of the branching point.

[0160] <Aspect G> The hydrogen engine of a working gas circulation type according to Aspect F, wherein a second control valve (second path switching means) 73 is provided to perform control such that the entire circulating gas discharged from the exhaust port and reaching the branching point flows in the bypass channel for heating when an amount of water vapor in the circulating gas discharged from the condenser is determined to be less than a predetermined value. It is also possible to control the second control valve so that when an amount of water vapor in the gas discharge from the condenser is small, a ratio (G4/G3) of a flow rate (G4) of gas flowing in the bypass channel for heating to a flow rate (G3) of gas flowing in the main circulation channel between the branching point and the merging point is higher than that when the amount of water vapor is larger.

[0161] <Aspect H> The hydrogen engine of a working gas circulation type according to Aspect G, wherein, even when the amount of water vapor in the circulating gas discharged from the condenser is determined to be less than a predetermined value, when the first control valve is controlled so that the entire circulating gas discharged into the main circulation channel via the outlet portion of the condenser flows in the bypass channel (the first moisture adsorption means), the second control valve is controlled so that the entire circulating gas discharged from the exhaust port and reaching the

branching point flows in the main circulation channel, without flowing in the bypass channel for heating.