THEREOF

The present invention relates to an internal combustion engine with reduced pressure common rail fuel supply system and a method of operating the same. In direct injection, a finer spray can be achieved by reducing the size of the injection holes, however, the injection pressure must in turn be increased. This pressure is around 2500 bar when injecting diesel oil and around 350 bar when injecting petrol. With the solution according to the invention, this pressure can be reduced and thus the efficiency of the motor can be increased.

State of the art:

US 20060097082A suggests a low injection pressure injector in which an atomizing aid plate is placed in front of the nozzle holes. The disadvantage of this solution is the large dead space between the nozzle hole and the combustion chamber, which causes a deposit forming in the dead space.

According to JP 2016128680A the injector uses multiple nozzle holes, therefore the injection pressure may be reduced, however, at the widened nozzle holes formed for the sake of a non-conflicting jet profile, cavitation develops.

According to U.S. Pat. No. 4,284,043A, fuel is heated in the injector by the heat of the combustion chamber. A surface of the second pressure chamber for heating is of cylinder head temperature because there is no thermal insulation between the chamber and cylinder head. A second surface has 480 °C, so the fuel in the chamber does not have uniform temperature and cavitation may form during injection. The heating does not take place between heat transfer surfaces which move relative to each other, therefore deposit is forming. The heating chamber occupies a large cylinder head surface. Multiple injections are not possible, the timing of the injection, the amount of fuel injected and the injection pressure cannot be controlled electronically. For pilot injection, i.e. for pre-injection, it uses a complex, nested injection needle structure. U.S. Pat. No. 20180142654 A1 relates to an arrangement of an injector in the cylinder head of an internal combustion engine, wherein the entire nozzle is separated from the cylinder head by an air gap and / or by an insert with a separate cooling and the nozzle front surface is also covered. It has no heat-absorbing surface, so the surface temperature of the lateral surface of the nozzle is lower than that of the cylinder head. Reduced injection pressure is not achievable with this solution.

CN 105332836 A describes a method for self-cleaning of an injector in which the fuel flows through a section of a helical path during injection. Due to the helical trajectory, the increased fuel path to the combustion chamber further increases the injection pressure need and is therefore disadvantageous.

JPH10252609 A reduces the heating of the injector by an element of good thermal conductivity inserted in the gap between the lateral surface of the nozzle and the cylinder head and has no heat absorbing surface, therefore the injection pressure cannot be reduced by this solution.

US 2011/0057049 A1 (also published as US 8511287B2) proposes injecting the fuel in a supercritical state, where the fuel is heated by electric current in the injector. The disadvantage of this solution is that it transfers additional heat to the cylinder head which is to be cooled anyway.

The object of the present invention is to provide a common rail direct injection internal combustion engine having an injector pressure less than applied heretofore.

The realization in the present invention lies in that heating the fuel will reduce its viscosity and therefore the injection pressure can be reduced. The heating of the fuel in the injector by the heat of the combustion chamber during the flow thereof from the nozzle base to the nozzle head is carried out as in a countercurrent heat exchanger by moving the heat transfer surfaces placed opposite to one another and having coking temperature with respect to one another thereby deposit forming is prevented, and the temperature of the nozzle head is kept on a tempereature above the coking temperature so as to make its surface self-cleaning and no dirt is deposited on the nozzle holes. With this solution, the object of the invention is achieved. The present invention therefore relates to an internal combustion engine with reduced pressure common rail direct injection having, inter alia, at least one cylinder, a piston therein capable of making alternating movement, a combustion chamber formed above the piston and a cylinder head closing it. At least one suction valve and at least one exhaust valve is arranged on the cylinder head. A driving gear is provided between the piston and a crankshaft to produce rotating movement. It has at least one injector that has a fuel connector, an electrical connector, and a nozzle body. A nozzle needle capable of axial movement is located in the nozzle body and there is a heat exchanging gap between the two. A nozzle base, a heat exchanging section, a nozzle head and a nozzle tip, is arranged axially in succession on the nozzle body. The engine has a fuel tank to which at least one low-pressure pump, a high-pressure pump and a rail are connected in series to one another. The fuel connector of the injector and a pressure regulator is connected to the rail. The engine contains an engine controller to which, inter alia, a temperature sensor, a pressure gauge, the pressure regulator and the electrical connector of the injector is connected.

The most important feature of the invention is that the heating of the fuel takes place in a narrow space between the surfaces moving relative to each other at the coking temperature between 150 °C and 450 °C. The heating takes place in a countercurrent heat exchanger. A part of the nozzle, which is the heat-absorbing section of the nozzle, is arranged to extend into the combustion chamber of the engine. This heat-absorbing part is called the nozzle head. The nozzle head is heated by the heat of the combustion chamber. The temperature of the nozzle head during operation is at least 450 °C and is therefore self-cleaning. The temperature at the nozzle base has a value below 150 °C. Typically, the heat exchange can also be enhanced by a heating rib and/or a screw rib. The nozzle occupies a small portion of the cylinder head surface and of the combustion chamber. Preferably several operating cycles are provided to heat the fuel, so it can be used at high speeds. The portion of the fuel under heating is separated from the heated fuel portions, so all parts of the injected fuel have the same temperature. It requires little heat-resistant material. It uses thermal insulation for efficient heating. The solution according to the invention will hereafter be described with reference to the following drawing, in which:

Figure 1 : is a section of a cylinder of an internal combustion engine showing the injector arrangement on the cylinder head,

Figure 2: is a sectional presentation of the nozzle for the petrol injector,

Figure 3: is a sectional presentation of the nozzle for the diesel oil injector.

Figure 4: is a sectional presentation of the nozzle for the injector of a high- stroke engine. Fig. 1 is a preferred embodiment of the invention, in which a cross-section of the combustion chamber 4 delimited by the cylinder 1 , the cylinder head 2 and the piston 3 is shown with the injector 15 and the nozzle body 16 arranged on the cylinder head 2. The figure shows the elements of a common-rail system: the fuel tank 5, the low-pressure pump 6, the temperature sensor 7, the high-pressure pump 8, the pressure gauge 9, the engine controller 10, the pressure regulator 11 , the pressure rail 12, the 13 electrical connectors, 14 fuel connectors.

Fig. 2 is an enlarged sectional view of a nozzle body 16 of a preferred embodiment of a gasoline injector 15, and Fig. 3 is an enlarged sectional view of a nozzle body 16 of a preferred embodiment of a diesel oil injector 15; the invention does not affect the rest of the injector 15. The two preferred embodiments are very similar, so the two figures will be described together.

The injector 15 is connected to the cylinder head 2 directly by the nozzle base 17 or via the sealing ring 30. The heat exchanging section 23 is arranged in the cylinder head 2. An air gap 25 is formed for thermal insulation between the heat exchanging section 23 and the cylinder head 2. The heat exchanging section 23 extends from the nozzle base 17 to the nozzle head 19. The heat chamber 24 is located between the inner surface of the nozzle head 19 and the nozzle needle 20. In the figure, the nozzle tip 21 is shown in the normal position and closes the path between the heat chamber 24 and the nozzle hole 28. The nozzle holes 28 are arranged at the tip 29 of the nozzle. Fleating ribs 27 are arranged on the nozzle head 19. A screw rib 26 is arranged on the nozzle needle 20. The fuel inlet 22 is located in front of the heat exchanging section 23. The size of the heat exchanging gap 31 is the distance between the nozzle needle 20 and the inner surface of the nozzle body 16. Optionally, a sleeve of a heat-insulating material may be used for thermal insulation in addition to or in place of the air gap 25. (Not shown.) Figure 4 is a sectional view of the injector of a high-stroke engine. In the case of a large stroke volume, there is enough space in the combustion chamber 4, so that a part of the heat exchanging section 23 is arranged to extend into the combustion chamber 4. The operation of the invention is described below:

The viscosity of liquids decreases exponentially with increasing temperature according to the Arrhenius relation: h = k1 * exp (k2 / T). In the formula, ki and k2 are constant characteristics of the substance, T is the absolute temperature. So, by heating the fuel, less pressure is enough for the injection because its viscosity is reduced. Deposition (coking) must be expected during heating. Deposition occurs between 150 °C and 450 °C. Surfaces are self-cleaning above 450 °C. Heating should take place without deposits, in a small space, in a short time, with good efficiency.

According to the invention, the fuel in the deposition heat region is heated in the heat exchanging gap 18 between the nozzle body 16 and the nozzle needle 20, where the axial movement of the nozzle needle 20 prevents the deposition. There is little space on the surface of the cylinder head 2, so the heat exchanging section 23 is extended axially and arranged in the cylinder head 2. Thus, a countercurrent heat exchanger is formed, the proper operation of which is ensured by the fact that the axial length of the heat exchanging section 23 is a multiple of the size of the heat exchanging gap 31. In the present invention, the axial length of the heat exchanging section 23 is at least three times, preferably at least ten times, more preferably at least twenty times, even more preferably at least thirty times the size of the heat exchanging gap 31. The fuel passes through the heat exchanging section 23 over several operating cycles until it is completely warmed up, so the time available for heat transfer increases. Good efficiency is achieved by thermally insulating the heat exchanging section 23 from the cylinder head 2 and therefore heating only the fuel with the heat taken from the combustion chamber 4. In the conventional case of the prior art, the lower limit of coking is targeted to avoid deposits, thus preventing the nozzle temperature from reaching 150 °C. Thus, any thermally conductive sleeve arranged in the cylinder head around the nozzle body 16, which may have been used in the previous solutions, is also placed in order to ensure that the nozzle temperature is kept below 150 °C. Similarly, if the nozzle is surrounded by an air gap, it is formed to arrange a cooling element. In the present invention, on the other hand, a heat- insulating element 25, such as an air gap 25 or a heat-insulating sleeve, surrounds the nozzle body 16 arranged in the cylinder head, thereby preventing the heat exchanging section 23 from being cooled by the cylinder head 2. The thickness of the air gap 25 exceeds the tolerance commonly used to place the nozzle in the cylinder head, and in the present invention it has a thickness (radial size) of at least 0,3 mm. If a heat-insulating sleeve is used, the sleeve thickness is also at least 0,3 mm. The heat-insulating element is arranged along the length of the heat exchanging section arranged in the cylinder head.

The fuel is fed from the fuel tank 5 by means of the low-pressure pump 6 and the high-pressure pump 8 to the rail 12 and from there to the fuel connector 14. From there, the high-pressure, cold fuel passes through the injector 15 to the inlet 22 and from there passes through the heat exchanging gap 18 to the heat chamber 24. As the nozzle needle 20 rises, it enters the combustion chamber 4 through the nozzle holes 28. The movement of the nozzle needle 20 is controlled by the engine controller 10 based on stored and measured signals. The nozzle head 19 is arranged to extend at least 4 mm into the combustion chamber 4. The nozzle head 19, the nozzle tip 29 and the nozzle needle tip 21 are heated by the heat of the combustion chamber 4. Their temperature during operation is above 450 °C and from there the heat is transferred to the heat exchanging section 23, the temperature of which decreases in the direction of the base 17 of the nozzle. The fuel is heated by passing it through the heat exchanging gap 18 in the opposite direction. The air gap 25 or a heat-insulating sleeve prevents the heat exchanging section 23 from being cooled by the cylinder head 2. By axially moving the nozzle needle 20, the nozzle body 16 is prevented from getting deposits while heat exchange is facilitated. The heat absorption of the nozzle head 19 is calibrated to reach a temperature of 450 °C. In the case of the nozzle head used in the previous solutions, it is also true that it extends into the combustion chamber 4 to a certain extent, but in general they try to create the smallest nozzle head size in order for the nozzle to absorb the least heat. However, the object of the present invention is the opposite, so that the nozzle head 19 is arranged to extend into the combustion chamber 4 at least 4 mm. To increase the heat absorption, heating ribs 27 are optionally arranged on the surface of the nozzle head 19. For lower heat requirements, heating ribs 27 can be omitted.

The heat exchanging section 23 and its length are dimensioned so that the temperature of the fuel flowing through it reaches 450 ° C at the heat chamber 24. Therefore, the selection of a high-speed steel material typical of previous solutions

- which is sufficient for nozzles kept below 150 °C - is not sufficient here. In the present application, the nozzle body 16, the nozzle tip 29, and the nozzle needle 20 are made of a heat-resistant material such as Wnr. 1 .4828 (H-8) heat-resistant steel or Nimonic 80A heat-resistant alloy. The heat exchange can be enhanced by a screw rib 26 arranged on the nozzle needle 20. Another advantage of this is that the passing fuel rotates the nozzle 20. Due to the rotation, no deposit forms at the closing surface of the nozzle needle tip 21 . Optionally, the screw 26 may be omitted.

When the engine is started, the nozzle head 19 temperature reaches 450 °C in just a few operating cycles and the engine is operated at reduced injection pressure. At the end of the compression stroke, the fuel is injected in several smaller doses per operating cycle. The pressure in the rail 12 is adjusted using measured and stored data by the motor controller 10 and the pressure regulator 11 .

The objects of the invention have been achieved and its and advantages are as follows:

- Due to lower pressure need, a high-pressure pump with lower energy consumption can be used, which increases the efficiency of the motor.

- It requires a small surface area of the cylinder head, so large valves can still be used. - Fuel at 450 °C is in a supercritical state and no drops are formed when injected into the combustion chamber at this temperature, so the size of the nozzle holes can be increased and the injection pressure is further reduced.

- Supercritical fuel does not cause cavitation when flowing through hot nozzle holes. - It can be used for currently produced internal combustion engines without modification of their structure.

- The solution according to the invention can also be applied afterwards by modifying the cylinder head and/or the nozzle of the injector.

- It also reduces particulate matter (PM) and NOx emissions. - It can be used in all areas where direct fuel injection into the combustion chamber is applied by injection liquid fuel.