Spark-ignition internal combustion engine with internal mixture formation for the combustion of a mixture of a gaseous fuel and air

Description

[0001] The invention relates to a spark-ignition internal combustion engine with internal mixture formation for the combustion of a mixture of a gaseous fuel and air to perform work. The gaseous fuel can preferably be hydrogen. The invention further relates to a motor vehicle, preferably a commercial vehicle, with such an internal combustion engine, as well as the use of such a spark-ignition internal combustion engine as a generator drive motor for power generation or for maritime applications.

[0002] Hydrogen can gain significant importance as a fuel due to its chemical properties and can be used particularly advantageously for torque generation in internal combustion engines. Accordingly, hydrogen combustion engines are already known from the prior art. These are combustion engines that run on hydrogen as fuel. The basis is the oxyhydrogen reaction (two parts hydrogen with one part oxygen) in a rotary piston cylinder. The basic concept of such combustion engines thus corresponds to that of conventional reciprocating piston engines with one or more cylinders. Reference is made to documents EP 1 647 684 A2 and DE 103 59 445 A1 only by way of example.

[0003] Another example is known from DE 10 2009 037160 A1.

[0004] For the use of hydrogen as a fuel, modified Otto cycle engines are typically used as spark-ignition internal combustion engines, although hydrogen combustion engines operating according to the diesel cycle are also known. In these spark-ignition engines, the hydrogen is introduced into the combustion chamber via a nozzle and ignited by a spark plug. This creates a flame front that spreads from the spark plug towards the cylinder wall.

[0005] Regarding mixture formation, hydrogen combustion engines are known to operate with external mixture formation (port injection), as well as hydrogen combustion engines that operate with internal mixture formation (direct injection).

[0006] In external mixture formation, pressurized hydrogen is injected into the intake manifold in gaseous form at a slight overpressure, upstream of the intake valves. In internal mixture formation, gaseous hydrogen is injected directly into the combustion chamber under pressure. The charge mixture is heated significantly during the compression phase and then ignited by a spark plug. Besides hydrogen engines, natural gas and biogas engines, as well as the use of other fuel gases, are also known.

[0007] The combustion speed of hydrogen is around 200 m / s and, under the same ambient conditions, is significantly higher than that of diesel and gasoline (approx. 20 m / s). Similar to conventional combustion engines, hydrogen engines can also experience combustion anomalies such as knocking, pre-ignition, or backfire. These anomalies tend to occur at "hot spots," i.e., particularly hot areas of the combustion chamber. Critical combustion chamber areas include the spark plug and the area around it, the exhaust valve head, valve stems, and the combustion chamber roof.

[0008] Accordingly, a disadvantage of hydrogen combustion engines known from the state of the art is that the components in the combustion chamber, especially the spark plug and the injection valve, are exposed to a high thermal load, which has a detrimental effect on their function and service life.

[0009] To solve this problem, WO 2015 / 138987 A1 proposes an injection ignition device with a prechamber, wherein the prechamber is in fluid communication with a combustion chamber of an internal combustion engine. This can be designed as an integrated, bolted, single unit suitable for operating high-performance spark-ignition direct-injection engines with gaseous fuels in dilute or lean mixtures. Furthermore, WO 2015 / 138987 A1 also discloses methods for combustion processes for operating a spark-ignition direct-injection engine with lean combustion, wherein injection events are to take place during the intake and compression strokes of the engine.

[0010] Furthermore, US Patent 3,572,297 A discloses an internal combustion engine that is operated by direct injection of hydrogen into its cylinders. In this process, hydrogen is mixed with a portion of the air in the cylinders to form a combustible mixture, which is ignited and burned simultaneously with the injection during part of the expansion stroke and, in some cases, during part of the compression stroke. Double-disc valves are used for the hydrogen injection; these valves open and close depending on the detected engine operating parameters.

[0011] From FR 3 061 743 A1, a valve ignition pre-chamber for an internal combustion engine is also known, which has a combustion chamber in which a main charge, more or less diluted with a neutral gas, is ignited. The pre-chamber has a stratification cavity into which ignition media open and into which a stratification injector can inject an easily ignitable pilot charge under pressure. Furthermore, a stratification valve can completely or partially close the stratification channel, particularly under the influence of the gas pressure prevailing in the combustion chamber.

[0012] It is an object of the invention to provide an improved internal combustion engine for burning a mixture of a gaseous fuel, preferably hydrogen, and air, which avoids the disadvantages of conventional gaseous fuel-operated internal combustion engines. In particular, the object of the invention is to provide such an internal combustion engine which reduces the thermal stress on components in the combustion chamber.

[0013] These problems are solved by a spark-ignition internal combustion engine with the features of the independent claim. Advantageous embodiments and applications of the invention are the subject of the dependent claims and are explained in more detail in the following description with partial reference to the figures.

[0014] According to a general aspect of the invention, a spark-ignition internal combustion engine with internal mixture formation is provided for the combustion of a mixture of gaseous fuel and air to perform work. The spark-ignition internal combustion engine (hereinafter also referred to simply as internal combustion engine or combustion motor) comprises at least one cylinder in which a combustion chamber is defined between a longitudinally movable piston and a cylinder head. The internal combustion engine further comprises, in a manner known per se, charge exchange valves for supplying air (air inlet valves) to the combustion chamber and charge exchange valves for removing exhaust gas (exhaust valves) from the combustion chamber.

[0015] Each of the at least one cylinder includes an injection valve and a spark plug located in the cylinder head.

[0016] The injection valve serves to direct the gaseous fuel into the combustion chamber, where the gaseous fuel mixes with air.

[0017] According to the invention, the injection valve is arranged at a distance from the combustion chamber in a feed channel that opens directly into the combustion chamber. This feed channel is hereinafter also referred to as the first feed channel to better distinguish it from a further feed channel described below, which is referred to as the second feed channel. In other words, the injection valve does not project into the combustion chamber or directly adjoin it, but is set back in the cylinder head. Gaseous fuel exiting through the injection valve towards the combustion chamber therefore does not enter the combustion chamber directly, but must travel at least a certain distance in the feed channel before the gaseous fuel can enter the combustion chamber.In accordance with the principle of internal mixture formation, the injection valve (or blow-in valve) is also called a direct injection valve because the gaseous fuel is injected under pressure directly into the combustion chamber via the supply channel or channels (internal mixture formation) and not, as with external mixture formation, injected in gaseous form into the intake manifold in front of the intake valves at a slight overpressure.

[0018] The internal combustion engine further comprises a spark plug, located in the cylinder head and having an ignition tip, which is arranged in a further feed channel opening into the combustion chamber, hereinafter referred to as the second feed channel, wherein the ignition tip is arranged at a distance from the opening of the second feed channel into the combustion chamber. In other words, the spark plug and its ignition tip do not protrude into the combustion chamber, but are set back from it in the cylinder head.

[0019] In summary, neither the spark plug nor the injection valve protrudes directly into the actual combustion chamber of the piston, but is recessed in the cylinder head. The arrangement of the spark plug and direct injection valve according to the invention offers the particular advantage that these components are subjected to less thermal stress due to their recessed position. Consequently, the spark plug achieves a longer service life, and the direct injection valve can be designed more cost-effectively.

[0020] Since, according to the invention, the direct injection valve does not protrude into the combustion chamber, there are also more design freedoms for the direct injection valve to optimize performance, and there is no need for a complex redesign of the cylinder head when using hydrogen instead of a liquid fuel. A further particular advantage is that the recessed arrangement of the gas injection valve and spark plug tip enables – as will be described in more detail below – the clean combustion of lean mixtures. The reason for this is that during the intake process, a richer mixture (lower lambda) can be generated in the area of ​​the second supply channel than in the combustion chamber, which can be ignited by the spark plug. This generates an ignition jet through the second supply channel towards the combustion chamber, which allows even lean mixtures with a high lambda to be burned as completely and cleanly as possible.This in turn allows for low nitrogen oxide emissions.

[0021] According to a particularly preferred embodiment, the gaseous fuel is hydrogen. Furthermore, the injection valve can be in fluid communication with a hydrogen storage device. Besides this exemplary application, the gaseous fuel can also be another type of gaseous fuel.

[0022] The first feed channel opens directly into the combustion chamber, thus not indirectly via the second feed channel. Accordingly, the two feed channels open into the combustion chamber at different points. The second feed channel therefore serves to supply gaseous fuel and air to the ignition tip, which is set back from the combustion chamber.

[0023] Furthermore, the second feed channel can open into the combustion chamber in a central area of ​​the combustion chamber roof. It is particularly advantageous if the second feed channel opens into the combustion chamber centrally at the combustion chamber roof. In this case, the cylinder head forms the combustion chamber roof, specifically the area of ​​the cylinder head facing the piston.

[0024] As explained above, the area bounded between the longitudinally movable piston and the cylinder head is referred to as the combustion chamber. The second and first intake ports are not considered part of the combustion chamber, even though combustion is ignited or initiated in the second intake port, similar to a spark plug with a pre-chamber.

[0025] The term "combustion chamber roof" refers to the cylinder head wall that borders the cylinder, through which the charge exchange (supply of air and fuel, expulsion of exhaust gas) takes place.

[0026] The spark-ignition internal combustion engine includes an engine control device designed to inject gaseous fuel via the injection valve during an intake process and to terminate this process before the start of the compression phase.

[0027] According to this principle, for example, gas injection of the gaseous fuel can occur during the intake stroke of the internal combustion engine, when the intake valves are open and the piston is moving downwards, i.e., away from the cylinder head. The engine control unit can control the gas injection valve so that it closes before the compression phase in the cylinder begins.

[0028] This offers the advantage that a large proportion, preferably almost 100%, of the fuel is gaseous in the area of ​​the spark plug tip. During the compression stroke, the hydrogen-air mixture from the combustion chamber is also forced into the supply channels, where the gaseous fuel present is compressed and mixed with the charge already in the cylinder or combustion chamber. In any case, this results in a richer mixture at the spark plug tip, thus increasing its ignitability. Similar to a spark plug with a pre-chamber, the combustion directly at the spark plug initiates a high-energy propagation of the combustion in the (main) combustion chamber via the second supply channel, ensuring that even lean mixtures with a high lambda value burn completely.

[0029] Because lean mixtures can also be burned cleanly, it was surprisingly discovered within the scope of the invention that a throttle valve located in the intake manifold is not absolutely necessary, as is otherwise customary for spark-ignition internal combustion engines. Accordingly, according to an advantageous aspect of the invention, the spark-ignition internal combustion engine can be provided without a throttle valve. Eliminating the throttle valve improves the efficiency of the internal combustion engine. In the case of exhaust gas recirculation and knowledge of the exhaust gas mass, this can also be taken into account as a control variable.

[0030] According to a further embodiment, the internal combustion engine can also include exhaust gas recirculation based on the donor cylinder principle, which is designed to recirculate exhaust gas from a subset of the engine's cylinders to an intake side. This allows, particularly in hydrogen combustion engines, nitrogen oxide emissions to be reduced to such an extent that, in some cases, exhaust aftertreatment systems are no longer necessary to comply with current emission limits. Exhaust gas recirculation also makes it possible to increase the compression ratio, thereby further improving the engine's efficiency. Furthermore, the recirculated exhaust gas can be cooled, for example, by means of a cooling device and / or a cooling circuit thermally coupled to the exhaust gas recirculation system.

[0031] To implement exhaust gas recirculation based on the donor cylinder principle, the internal combustion engine can, for example, have at least one exhaust gas turbocharger, which includes a compressor and a turbine, as well as a charge air line for supplying compressed air to the engine. The engine's at least one cylinder comprises a first cylinder group and a second cylinder group, with the second cylinder group operating according to the donor cylinder principle. An exhaust manifold is provided, which has a first section for collecting exhaust gases from the first cylinder group and a second section for collecting exhaust gases from the second cylinder group. Furthermore, a first exhaust line is provided, which connects the first section of the exhaust manifold to the turbine, with a return line for recirculating exhaust gases from the second section of the exhaust manifold into the charge air line.

[0032] Furthermore, the piston of the spark-ignition internal combustion engine can have a concave recess. Optionally, a convex protrusion can be provided within the concave recess. These measures improve efficiency.

[0033] According to another aspect, the first feed channel can have a constant cross-section, preferably with a length greater than its cross-sectional width. Furthermore, the second feed channel can have a constant cross-section, preferably with a length greater than its cross-sectional width. Additionally, the first feed channel and / or the second feed channel can be formed by a bore or a core casting.

[0034] The invention further relates to a motor vehicle with a spark-ignition internal combustion engine as described in this document. The motor vehicle can be a commercial vehicle, such as a truck or bus.

[0035] Further preferred applications of the invention include the use of a spark-ignition internal combustion engine, as described in this document, as an internal combustion engine, in particular a generator drive engine, for power generation or for maritime applications. The preferred embodiments, aspects, and features of the invention described above can be combined with one another as desired. Further details and advantages of the invention are described below with reference to the accompanying drawing. It shows: Figure 1 shows a schematic detail view in cross-section of a cylinder head area of ​​an internal combustion engine, not according to an embodiment of the invention.

[0036] The spark-ignition internal combustion engine 1 operates on the principle of internal mixture formation to combust a mixture of a gaseous fuel, in this case hydrogen, and air, thereby producing work. The internal combustion engine 1 is thus a hydrogen engine. The internal combustion engine 1 comprises at least one cylinder 2, in which a combustion chamber 3 is bounded between a longitudinally movable piston 4 and a cylinder head 6. The direction of movement of the piston 4 is schematically represented by arrow 16. The piston 6 has a concave recess 5.

[0037] Figure 1Figure 1 shows a schematic detail view in cross-section of only one cylinder head area of ​​a cylinder 2 of the internal combustion engine 1. However, each cylinder 2 includes a spark plug 9 arranged in the cylinder head 6, which has an ignition tip 10 and is located in the second feed channel 11 opening into the combustion chamber. The opening of the second feed channel 11 into the combustion chamber 3 is marked with reference numeral 12. The ignition tip 10 is spaced apart from the opening 12 of the second feed channel 11 into the combustion chamber 3.

[0038] Furthermore, each of the cylinders 2 includes an injection valve 7 arranged in the cylinder head 6, which may be designed as a control valve. The injection valve 7 is arranged at a distance from the combustion chamber 3 in a first supply channel 8. The first supply channel 8 opens indirectly into the combustion chamber 3 via the second supply channel 11. The injection valve 7 is in fluid communication with a hydrogen storage device 14 via a line 15.

[0039] The first feed channel 8 opens into the combustion chamber 3 between the ignition tip 10 and the opening 12 of the second feed channel 11. The opening of the first feed channel 8 into the second feed channel 11 is marked with reference numeral 13. The opening 12 of the second feed channel 11 into the combustion chamber 3 is located centrally on the combustion chamber roof 17.

[0040] Due to its high ignitability, the hydrogen is intended to be introduced directly into the combustion chamber 3, which is done via the supply channels 8, 11.

[0041] In summary, neither the spark plug 9 nor the injection valve 7 protrudes directly into the actual combustion chamber 3 of the piston, but are recessed in the cylinder head 6 and thus spaced apart from the actual (main) combustion chamber 3. The arrangement of the spark plug 9 and the direct injection valve 7 according to the invention offers the particular advantage that these components are subjected to less thermal stress due to their recessed position. Accordingly, the spark plug 9 achieves a longer service life, and the direct injection valve 7 can be designed more cost-effectively.

[0042] The internal combustion engine 3 further comprises two charge exchange valves on each cylinder for supplying air (air inlet valves) into the combustion chamber 3 and charge exchange valves for removing exhaust gas (exhaust valves) from the combustion chamber 3, which are not shown and can be designed in a manner known per se.

[0043] The gas injection valve 7 is connected to and controlled by an engine control unit 20. The engine control unit 20 can be the engine control module. The engine control unit 20 is configured to inject gaseous fuel via the injection valve during the intake process and preferably to terminate this injection before the start of the compression phase. For this purpose, the engine control unit 20 controls the gas injection valve 20 accordingly to open or close it.

[0044] The following describes the ignition operation of the internal combustion engine.

[0045] A particularly advantageous method is the direct introduction of hydrogen into the combustion chamber 3 during the intake stroke. The injection occurs in the direction of airflow after the intake valve (not shown). The gas injection takes place during the intake process of the internal combustion engine 1, i.e., when the intake valve (not shown) is open for air and the piston 4 is moving downwards. For this purpose, the injection valve 7 is opened. The injection valve 7 is closed again before the compression phase begins in cylinder 2. Thus, there is almost 100% hydrogen in the area of ​​the spark plug tip 10 when the compression phase begins, as the hydrogen preferentially accumulates there through the supply channels 8, 11. Some of the hydrogen enters the combustion chamber via the supply channels 8, 11 and mixes there with the air entering through the intake valves (not shown) (internal mixture formation).During the compression stroke, the hydrogen-air mixture is also forced into channels 8 and 11, the hydrogen present there is compressed and also mixed with the charge present in the cylinder.

[0046] In any case, the mixture at the spark plug tip 10 is "richer," thereby increasing its ignitability. Similar to a pre-chamber spark plug, the combustion directly at the spark plug initiates a high-energy propagation of the combustion in the main combustion chamber 3 via the feed channel 11. This energy is significantly greater than the ignition energy of a spark plug and ensures that even lean mixtures burn completely in the combustion chamber 3 with a high lambda value.

[0047] The recessed arrangement of the spark plug 9 and the injection valve 7 from the combustion chamber 3 thus leads to hydrogen enrichment in the second supply channel 11 and, upon ignition, to a kind of "ignition jet" that propagates through the supply channel 11 into the combustion chamber 3. Because a reduced lambda value always prevails at the spark plug 9 in the illustrated design, even very lean mixtures are reliably and completely combusted in the combustion chamber 3 via the "ignition jet." This principle also allows for the elimination of the throttle valve, as already mentioned above.

[0048] The engine control unit also regulates the driver's input, i.e., torque and / or engine speed, in a familiar manner. In the case of a hydrogen combustion engine, the amount of fuel injected depends on the accelerator pedal position, but also takes into account the amount of combustion air (lambda). For this purpose, the air mass and, in the case of exhaust gas recirculation, the exhaust gas mass are measured. Nitrogen oxide emissions can also be influenced by the air-fuel ratio (lambda). Generally, the higher the lambda value, the lower the nitrogen oxide emissions.

[0049] The internal combustion engine 1 can also feature exhaust gas recirculation based on the donor cylinder principle, designed to recirculate exhaust gas from a subset of cylinders 2 of the internal combustion engine 1 to an intake side. In this case, for example, in a 6-cylinder engine, the entire exhaust gas from one cylinder is recirculated directly back to the intake side. This achieves a stable exhaust gas recirculation ratio (100 / 6). The exhaust gas turbocharger then only receives the exhaust gas mass from 5 cylinders. The exhaust gas recirculation line can typically be shut off by a shut-off valve. The recirculated exhaust gas can also be cooled.

[0050] The recessed arrangement of spark plug 9 and injection valve 7 allows existing engines, especially common-rail diesel engines with side-feed injectors, to be converted to hydrogen operation relatively easily. Due to the design similarities, it is possible to use the same cylinder head castings for both diesel and hydrogen engines. For example, a single cylinder head blank can be used to produce either a cylinder head for a diesel engine with a common-rail injector and so-called side-feed connection, or the cylinder head 6 for the hydrogen engine or the internal combustion engine 1 according to [reference to relevant section]. Figure 1 .

[0051] Such an internal combustion engine 1, or such a hydrogen engine, is not only suitable for motor vehicles (trucks and buses), but is also suitable as a generator drive motor for power generation or for maritime applications. If the hydrogen is produced regeneratively, the internal combustion engine 1 can be described as a CO₂-neutral internal combustion engine and can make a significant contribution to low-emission power generation, especially during periods of low wind and solar output.

[0052] Although the invention has been described with reference to specific embodiments, it is apparent to a person skilled in the art that various modifications can be made without departing from the scope of the invention. Consequently, the invention is not intended to be limited to the disclosed embodiments, but rather to encompass all embodiments falling within the scope of the appended claims. Reference symbol list

[0053] 1 Internal combustion engine 2 Cylinder 3 Combustion chamber 4 Piston 5 Piston bowl 6 Cylinder head 7 Direct injection valve 8 First feed port 9 Spark plug 10 Ignition tip 11 Second feed port 12 Opening of second feed port into combustion chamber 13 Opening of first feed port into second feed port 14 Hydrogen storage device 15 Gas inlet 16 Piston movement direction 20 Engine control device

Claims

1. A spark-ignition internal combustion engine (1) with internal mixture formation for the combustion of a mixture of a gaseous fuel and air under working power, comprising: at least one cylinder (2) in which a combustion chamber (3) is defined between a piston (4) arranged to move longitudinally and a cylinder head (6), each of the at least one cylinder (2) comprising: a direct injection valve (7) arranged in the cylinder head (6), which is arranged at a distance from the combustion chamber (3) in a first supply passage (8) opening directly into the combustion chamber (3); and an ignition plug (9) arranged in the cylinder head (6) and having an ignition tip (10), which is arranged in a second supply passage (11) opening into the combustion chamber, the ignition tip (10) being arranged at a distance from the opening (12) of the second supply passage (11) into the combustion chamber (3); an engine control device (20) which is configured to perform a gas injection of the gaseous fuel by the direct injection valve (7) during an intake process and to terminate it before the start of the compression phase; characterised in that the first supply passage (8) opens into the combustion chamber (3) at a different location than the second supply passage (11).

2. The spark-ignition internal combustion engine (1) according to claim 1, a) wherein the gaseous fuel is hydrogen; and / or b) wherein the direct injection valve (7) is in fluid communication with a hydrogen storage device (14).

3. The spark-ignition internal combustion engine (1) according to one of the preceding claims, wherein the second supply passage (11) opens into the combustion chamber (3) in a central region of a combustion chamber roof (17), preferably opens into the combustion chamber (3) in the centre of the combustion chamber roof (17).

4. The spark-ignition internal combustion engine (1) according to one of the preceding claims, wherein the internal combustion engine comprises no throttle valve.

5. The spark-ignition internal combustion engine (1) according to one of the preceding claims, comprising an exhaust gas recirculation according to the donor cylinder principle, which is configured to recirculate exhaust gas from a subset of the cylinders of the internal combustion engine to an intake side.

6. The spark-ignition internal combustion engine (1) according to one of the preceding claims, wherein the piston has a concave depression (5).

7. The spark-ignition internal combustion engine (1) according to claim 6, wherein a convex projection is provided within the concave depression.

8. A motor vehicle, preferably a commercial vehicle, such as a lorry or bus, with a spark-ignition internal combustion engine according to one of the preceding claims.

9. A use of a spark-ignition internal combustion engine (1) according to one of claims 1 to 7 as a generator drive engine for power generation or for maritime applications.

10. A use of a spark-ignition internal combustion engine (1) according to one of claims 1 to 7, wherein the gaseous fuel is injected under pressure directly into the combustion chamber (3) via the first supply passage (8).