Field of the Invention

[0001] The present application relates to regulating gaseous fuel pressure in internal combustion engines where gaseous fuel supply pressure is greater than inj ection pressure.

Background of the Invention

[0002] Gaseous fuels can be stored in storage vessels at elevated pressures to increase the mass of fuel available for an internal combustion engine. When the internal combustion engine powers a vehicle, the higher the storage pressure the greater the range of operation for the vehicle. Similarly, as the gaseous fuel is consumed by the engine and pressure decreases in the storage vessel, vehicle range is extended when the internal combustion engine can be made to operate at lower minimum pressures. A gaseous fuel is any fuel that is in a gas state at standard temperature and pressure, which in the context of this application is 20 degrees Celsius (°C) and 1 atmosphere (atm). An exemplary gaseous fuel is natural gas, which when stored in a gas state in a pressurized storage vessel (e.g. a pressure cylinder) is referred to as compressed natural gas (CNG). Other examples of gaseous fuels include butane, ethane, hydrogen, propane, and mixtures thereof, and as would be known to one skilled in the art there are many other such examples. [0003] Gaseous fuel storage pressure is reduced and regulated to one or more predetermined pressures that are suitable for the engine to operate. Fuel system components can be made more efficient and cost effective when they are designed to operate within a narrower range of operating pressures compared to operating across the full range of pressures between minimum and maximum storage pressure. Fuel injectors can introduce predetermined amounts of gaseous fuel with greater accuracy when the pressure of gaseous fuel supplied is within the narrower range, thereby improving engine efficiency and fuel economy, and reducing emissions. [0004] Gaseous fuel temperature decreases when gaseous fuel pressure is reduced from storage pressure to the operating pressure of the engine due to the Joule- Thomson effect. The temperature change can be significant when the operating pressure is much less than storage pressure, causing moisture and constituents of the gaseous fuel (such as hydrates) in and around the pressure regulating apparatus to freeze, which can lead to reduced flow and performance of the apparatus, and in the worst case blocked flow can result. This problem is exacerbated when the mass flow rate of gaseous fuel is high. To decrease the likelihood of freezing a heat exchanger can be employed to regulate the temperature of the gaseous fuel, either entering or leaving the pressure regulating apparatus, thereby mitigating the Joule-Thomson effect. It is known to employ engine coolant as a heat exchange medium in the heat exchanger. Waste heat from the engine is captured by the engine coolant as it circulates through what is commonly known as the "water jacket" of the engine. Before the waste heat in the engine coolant is rejected to atmosphere (cooled) through a radiator, it can be made to circulate through the heat exchanger where the waste heat can be transferred to the gaseous fuel thereby elevating gaseous fuel temperature and mitigating the Joule-Thomson effect. In some applications, however, the pressure regulating apparatus is remotely located from the engine, such as when the gaseous fuel storage vessel is located in the rear of the vehicle. In these situations it is expensive and impractical to extend the plumbing for the engine coolant to the pressure regulating apparatus. Alternatively, heat exchangers that supply heat with electric heaters, powered from electrical energy generated by the engine, can be employed. It is significantly more cost effective and practical to extend electric power cables from the engine to remotely located storage vessels. One drawback with electrically heated heat exchangers is reduced efficiency compared to the engine coolant heat exchanger. Instead of employing waste heat already generated from engine operation, the engine must now consume additional fuel to generate electrical energy for consumption by the electrical heater. The reduced efficiency of electrical heater heat exchangers becomes increasingly undesirable as the maximum storage pressure and peak fuel flow rates increase. [0005] The state of the art is lacking in techniques for mitigating the Joule- Thomson effect in pressure regulators. The present method and apparatus provides an improved technique for gaseous fuel pressure regulation in an internal combustion engine.

Summary of the Invention [0006] An improved method for reducing gaseous fuel pressure from a first pressure to a second pressure in a gaseous fuel system for an internal combustion engine includes passively heating the gaseous fuel at the first pressure; and reducing the pressure of the heated gaseous fuel to the second pressure. The gaseous fuel temperature at the second pressure is maintained above a first predetermined temperature and the second pressure is maintained within a first predetermined range of tolerance. The first pressure can be a storage pressure for the gaseous fuel, or an intermediate pressure between the storage pressure and the second pressure, and the second pressure can be an injection pressure for the gaseous fuel. The first predetermined temperature can be a freezing temperature of water and a freezing temperature of a constituent of the gaseous fuel. The method can also include reducing a storage pressure of gaseous fuel to the first pressure before passively heating the gaseous fuel.

[0007] In an exemplary embodiment a vortex heater is employed to passively heat the gaseous fuel. The gaseous fuel at the first pressure is fluidly communicated through a modified vortex tube, where a temperature of the gaseous fuel fluidly exiting the modified vortex tube is greater than a temperature of the gaseous fuel entering the modified vortex tube.

[0008] In another exemplary embodiment the method can include skipping the step of passively heating when the first pressure is below a predetermined pressure, or when a difference between the first pressure and the second pressure is below a predetermined value, and there is reduced need for heating the gaseous fuel. The method can also include regulating the gaseous fuel temperature at the second T/CA2015/051145

- 4 - pressure to a second predetermined temperature within a second predetermined range of tolerance by selectively skipping the step of passively heating.

[0009] An improved apparatus for reducing gaseous fuel pressure from a first pressure to a second pressure in a gaseous fuel system for an internal combustion engine includes a passive heating apparatus receiving gaseous fuel at the first pressure; and a pressure reducing apparatus fluidly receiving heated gaseous fuel the passive heating device and supplying the gaseous fuel at the second pressure within a first predetermined range of tolerance. The gaseous fuel temperature at the second pressure is maintained above a first predetermined temperature. The gaseous fuel can be at least one of butane, ethane, hydrogen, natural gas and propane, and as would be known by those skilled with the technology other types of gaseous fuel can be employed.

[0010] In an exemplary embodiment the passive heating apparatus is a vortex heater including a modified vortex tube having an inlet fluidly receiving gaseous fuel at the first pressure, and a distal end and a proximal end relative to the inlet. The distal end is blocked such that gaseous fuel entering the modified vortex tube travels towards the distal end in a vortex where it is reflected back towards the proximal end, where there is an outlet for the gaseous fuel.

[0011] In another exemplary embodiment, the apparatus includes a fluid switch switchable between a first position and a second position when a predefined enabling condition is met. The fluid switch communicating gaseous fuel at the first pressure to the passive heating apparatus in the first position, and fluidly communicating gaseous fuel at the first pressure to the pressure reducing apparatus in the second position. The predefined enabling condition is met when a difference between the first pressure and the second pressure is less than a predetermined value. The fluid switch can comprise a three-way valve. The three-way valve can be pressure actuated and switches between the first position and the second position automatically when the predefined enabling condition is met. [0012] The apparatus can further include a controller and a first pressure sensor that sends signals representative of the first pressure to the controller. The controller is operatively connected with the fluid switch and programmed to determine a difference between the first pressure and the second pressure based on the signals from the first pressure sensor and a target value for the second pressure; determine that the predefined enabling condition is met when the difference is less than a predetermined value; and command the fluid switch to switch to the second position when the predefined enabling condition is met. Instead of or in addition to employing a target value for the second pressure, the apparatus can comprise a second pressure sensor that sends signals representative of the second pressure to the controller, and the controller can be further programmed to determine the difference between the first pressure and the second pressure based on the signals from the first and second pressure sensors.

[0013] In yet another exemplary embodiment, the apparatus further comprises a fluid switch switchable between a first position and a second position. The fluid switch fluidly communicating gaseous fuel at the first pressure to the passive heating apparatus in the first position, and fluidly communicating gaseous fuel at the first pressure to the pressure reducing apparatus in the second position. There is a controller operatively connected with the fluid switch; and a temperature sensor sending signals representative of gaseous fuel temperature downstream from the pressure reducing apparatus to the controller. The controller is programmed to selectively command the fluid switch between the first and second positions to maintain the gaseous fuel temperature downstream from the pressure reducing apparatus at a second predetermined temperature within a second predetermined range of tolerance. [0014] The still another exemplary embodiment the pressure reducing apparatus is a second stage pressure reducing apparatus, the apparatus further includes a gaseous fuel supply storing gaseous fuel at a storage pressure and a first stage pressure reducing apparatus fluidly connected with the gaseous fuel supply to reduce gaseous fuel pressure from the storage pressure to the first pressure. There can be a fluid switch switchable between a first position and a second position when a predefined enabling condition is met. The fluid switch fluidly communicating gaseous fuel at the storage pressure to the first stage pressure reducing apparatus in the first position, and fluidly communicating gaseous fuel at the storage pressure to the second stage pressure reducing apparatus in the second position. Brief Description of the Drawings

[0015] FIG. 1 is a schematic view of a fuel system for an engine according to a first embodiment.

[0016] FIG. 2 is a schematic view of a vortex heater according to one embodiment. [0017] FIG. 3 is a cross-sectional view of a vortex tube in the vortex heater of FIG. 2 taken along line 3-3'.

[0018] FIG. 4 is a schematic view of a fuel system for an engine according to a second embodiment.

[0019] FIG. 5 is a schematic view of a fuel system for an engine according to a third embodiment.

[0020] FIG. 6 is a schematic view of a fuel system for an engine according to a fourth embodiment.

[0021] FIG. 7 is a schematic view of a fuel system for an engine according to a fifth embodiment. Detailed Description of Preferred Embodiment(s)

[0022] Referring to FIG. 1, gaseous fuel system 10 is shown according to a first embodiment for supplying gaseous fuel to internal combustion engine 50. Gaseous fuel is stored in fuel supply 20 at pressures greater than the operating pressure required by internal combustion engine 50. A compressed natural gas (CNG) storage tank can be filled to a storage pressure of at least 3,000 pounds per square inch (psi) and some storage vessels are rated for pressures up to 10,000 psi. Pressure reducing apparatus 40 reduces and regulates the pressure of the gaseous fuel to a pressure suitable for use by the engine. In a preferred embodiment apparatus 40 is a pressure regulator. For engines to introduce a gaseous fuel into the intake system the injection pressure can be between a range of 50 psi and 500 psi depending upon application requirements and engine operating conditions, and a similar pressure range or a pressure range with a higher maximum pressure can be used for early cycle direct fuel injection depending on the injection timing. Vortex heater 30 is a passive heating - apparatus that passively heats the gaseous fuel, increasing gaseous fuel temperature upstream of pressure regulator 40 to mitigate the Joule-Thomson effect occurring as a result of the pressure reduction across the pressure regulator. Vortex heaters operate based on the principal of the Ranque-Hilsch vortex tube, as is well known by those familiar with the technology. The vortex tube was invented by Georges J. Ranque who obtained United States Patent No. 1,952,281. As used herein, passive heating is defined as employing the pressure of a fluid to heat the fluid, wherein pressure is defined as potential energy per unit volume. The vortex heater passively heats the gaseous fuel since no external source of energy is required other than the pressure potential energy stored in the pressurized gaseous fuel in fuel supply 20. Vortex heater 30 comprises an inlet and a single outlet, where the temperature of the gaseous fuel at the outlet is greater than gaseous fuel temperature at the inlet. This is in contrast to the vortex tube, which comprises an inlet and two fluid outlets, where the fluid temperature at one outlet is cold and at the other outlet is hot relative to the fluid temperature at the inlet.

[0023] An exemplary vortex heater 30 is illustrated in FIG. 2, according to one embodiment. Vortex heater 30 comprises modified vortex tube 60 that includes one inlet and one outlet, as will be explained below, comprising elongate tube portion 70 and annulus portion 80. Tube portion 70 is received through bore 90 in annular housing 100 such that annulus portion 80 abuts an inside wall of the housing. Modified vortex tube 60 is fluidly sealed with respect to bore 90. End piece 110 threadedly engages housing 100 to secure modified vortex tube 60 in place. Inlet 120 is fluidly connected with fuel supply 20, and outlet 130 is fluidly connected with pressure regulator 40. A plurality of tangential passageways 140 extend from an outer periphery of annulus portion 80 towards the hollow interior of tube portion 70. Gaseous fuel received in inlet 120 circulates around annular space 150, and as it does enters the various passageways 140. The angle of passageways 140 is such that the trajectory of the gaseous fuel upon emerging within modified vortex tube 60 creates a vortex that first flows to distal end 160 where, since the distal end is blocked, is reflected back towards proximal end 170. As the gaseous fuel flows back to proximal end 170 it interacts with the oncoming gaseous fuel causing its temperature to increase. The gaseous fuel flows through proximal end 170 and out of vortex heater 30 through outlet 130.

[0024] There is a pressure drop in the gaseous fuel across vortex heater 30. When gaseous fuel storage pressure in fuel supply 20 is sufficiently larger than the operating pressure of the engine, the pressure drop across vortex heater 30 does not adversely influence the operation of pressure regulator 40, where the pressure is further reduced and regulated to the operating pressure of engine 50. However, as gaseous fuel storage pressure in fuel supply 20 drops below a predetermined level the pressure drop across vortex heater 30 begins to affect the performance of pressure regulator 40 and limits the operating range of engine 50. [0025] Referring now to FIG. 4, fuel system 12 is illustrated according to a second embodiment which is similar to the previous embodiment and like parts in this and subsequent embodiments have like reference numerals and may not be described in detail, if at all. Fluid switch 200 is employed to increase the range of engine 50 by selectively directing the flow of gaseous fuel through or around vortex heater 30 as a function of storage pressure and/or operating pressure. Controller 210 is operatively connected with fluid switch 200 and commands the fluid switch between a first position and a second position. In the first position, fluid switch 200 fluidly connects fuel supply 20 with vortex heater 30, and in the second position, the fluid switch fluidly connects the fuel supply directly with pressure regulator 40 bypassing the vortex heater. Controller 210 receives signals representative of gaseous fuel pressure from first pressure sensor 220 and commands fluid switch 200 between the first and second positions accordingly as a function of gaseous fuel pressure. First pressure sensor 220 sends signals representative of a first pressure of gaseous fuel, which can be the storage pressure in fuel supply 20, or alternatively it can be the pressure downstream of fuel supply 20 (for example after shut-off and/or safety valves associated with the fuel supply) but upstream of vortex heater 30. The first pressure can also be an intermediate pressure after a pressure reduction from gaseous fuel storage pressure, as will be discussed in more detail below. In a preferred embodiment pressure regulator 40 regulates pressure of the gaseous fuel to a second pressure that can be one or more predefined target values. Controller 210 commands fluid switch 200 to the second position when a predefined enabling condition is met. The predefined enabling condition is met when a difference between the first pressure (storage pressure) and the second pressure (injection pressure) is less than a predetermined value. In an exemplary embodiment, when the second pressure is a predefined target value, such as when pressure regulator 40 regulates to a fixed pressure, then the predefined enabling condition is met when the first pressure is less than the sum of the predefined target value and the predetermined value.

[0026] In other embodiments second pressure sensor 230 can be employed to determine gaseous fuel pressure downstream of pressure regulator 40 (the second pressure). Sensor 230 sends signals representative of the second pressure to controller 210, which uses these signals in the determination of the difference between the first and second pressures. This is particularly useful when pressure regulator 40 is a variable pressure regulator that can be commanded to selectively provide a range of output pressures, or a multi-step regulator providing a series of output pressures. In a preferred embodiment controller 210 is operatively connected with pressure regulator 40 to command the pressure regulator to regulate the output pressure to two or more target values.

[0027] Alternatively to pressure sensors 220 and 230, or additionally, temperature sensor 240 can be employed by controller 210 to determine when to change fluid switch 200 between the first and second positions. Temperature sensor 240 sends signals to controller 210 representative of gaseous fuel temperature downstream from pressure regulator 40. When gaseous fuel temperature is below a predetermined temperature, controller 210 commands fluid switch 200 to the first position where gaseous fuel is communicated through vortex heater 30 to heat the fuel, and when gaseous fuel temperature is equal to or greater than the predetermined temperature the controller commands fluid switch to the second position. Controller 210 can employ hysteresis to reduce oscillations between the first and second positions. Gaseous fuel temperature can be regulated to within a predetermined range of tolerance by employing temperature sensor 240, in addition to reducing the likelihood of freezing due to the Joule-Thomson effect. In other embodiments, temperature sensor 240 can be located further upstream, such as before pressure regulator 40 or before vortex heater 30, where gaseous fuel temperature downstream of the pressure regulator can be correlated to these upstream temperatures as a function of the pressure drop across the respective components and gaseous fuel flow rate. [0028] The dashed lines in FIG. 4 between controller 210 and other components represent electrical connections, and the arrows at the ends of these dashed lines represent the direction of communication, and such communication between the controller and these components can comprise commands and/or status information. As would be known by those familiar with the technology, although not explicitly illustrated in the figures, controller 210 can be connected with other components. Controller 210 can comprise both hardware and software components. The hardware components can comprise digital and/or analog electronic components. In the embodiments herein controller 210 comprises a processor and memories, including one or more permanent memories, such as FLASH, EEPROM and a hard disk, and a temporary memory, such as SRAM and DRAM, for storing and executing a program. As used herein, the terms algorithm, module and step refer to an application specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that execute one or more software or firmware programs, a combinational logic circuit, and/or other suitable components that provide the described functionality.

[0029] Referring now to FIG. 5, engine system 13 is illustrated according to a third embodiment. Fluid switch 300 is a pressure sensing three-way valve that is pressure actuated between the first and second positions. When the first pressure, for example gaseous fuel storage pressure, is above a threshold value fluid switch 300 is in the first position and fluidly communicates gaseous fuel through vortex heater 30 where the fuel is heated before entering pressure regulator 40. However, when the first pressure is below the threshold value, fluid switch 300 is actuated into the second position and fluidly communicates gaseous fuel around (by-passes) vortex heater 30 directly to pressure regulator 40. In an exemplary embodiment the threshold value can be equal to the sum of the second pressure (injection pressure) and the predetermined value discussed previously.

[0030] Referring now to FIG. 6, engine system 14 is illustrated according to a fourth embodiment that is similar to the embodiment of FIG. 1 and further includes first stage pressure reducing apparatus 25. First stage pressure reducing apparatus 25 is employed when the gaseous fuel storage pressure in fuel supply 20 is above a threshold pressure that limits the volumetric flow rate and the velocity of gaseous fuel through vortex heater 30, which can reduce the heating effect on the gaseous fuel. By reducing the pressure below the threshold pressure the volumetric flow rate through vortex heater 30 increases. First stage pressure reducing apparatus 25 reduces the gaseous fuel storage pressure to an intermediate pressure between the storage pressure and the second pressure (for example, the injection pressure). Pressure reducing apparatus 40 is a second stage pressure reducing apparatus that regulates the pressure of gaseous fuel more finely than first stage pressure reducing apparatus 25, which provides more of a course pressure reduction. Both pressure reducing apparatuses 25 and 40, or either one, can be arranged such that they are heated by the heated gaseous fuel from vortex heater 30. For example, both apparatuses 25 and 40, or either one, can share a common body (not shown) with vortex heater 30 that can conduct the heat 45

- 12 - generated by the vortex heater to maintain the temperature of these individual components above a predetermined level.

[0031] Referring now to FIG. 7, engine system 15 is illustrated according to a fifth embodiment that is similar to the embodiment of FIG. 4. Like the embodiment of FIG. 6, first stage pressure reducing apparatus 25 is employed when gaseous fuel storage pressure in fuel supply 20 is above a threshold pressure that limits the volumetric flow rate and the velocity of gaseous fuel through vortex heater 30, which can reduce the heating effect on the gaseous fuel. By reducing the pressure below the threshold pressure the volumetric flow rate through vortex heater 30 increases. First stage pressure reducing apparatus 25 is effectively located downstream from fluid switch 200 since the threshold pressure associated with first stage pressure reducing apparatus 25 (when storage pressure is reduced to improve the heating effect of vortex heater 30) is greater than the predetermined pressure value associated with fluid switch 200 (when storage pressure so low that there is no need for vortex heater 30). When fluid switch 200 is activated to divert the flow of gaseous fuel around vortex heater 30, the fuel storage pressure is below the predetermined level (that is it's too low) and therefore there is no need to reduce the pressure with first stage pressure reducing apparatus 25. However, first stage pressure reducing apparatus 25 can be located upstream of fluid switch 200 in other embodiments since in conventional pressure reducing apparatuses when the pressure is too low the pressure reducing apparatus will go wide open and have negligible effect on gaseous fuel pressure. In other embodiments, the electronically controlled fluid switch 200 can be replaced by fluid switch 300, the pressure sensing three-way valve, as discussed with reference to FIG. 5.

[0032] While particular elements, embodiments and applications of the present invention have been shown and described, it will be understood, that the invention is not limited thereto since modifications can be made by those skilled in the art without departing from the scope of the present disclosure, particularly in light of the foregoing teachings.