Method for operating a gas engine, and gas engine

Abstract

The invention relates to a gas engine (20) having a cylinder with a combustion chamber (21) enclosed by a cylinder jacket, a combustion chamber roof and a cylinder base; an inlet valve and an outlet valve as gas exchange valves; and an injector (1) for injecting combustion gas into the combustion chamber. In a first setting, the injector (1) generates a combustion gas flow (CS) at a distance to the combustion chamber roof and, in a second setting, generates a combustion gas flow (HS) on the combustion chamber roof. The invention also relates to a method for operating such a gas engine.

Description

[0001] Method for operating a gas engine and gas engine

[0002] The invention relates to a method for operating a gas engine with a cylinder having a combustion chamber enclosed by a cylinder jacket, a combustion chamber roof, and a cylinder base, with an inlet valve and an exhaust valve as gas exchange valves, and with an injector for injecting fuel gas into the combustion chamber. The invention further relates to a gas engine.

[0003] A gas engine with a gas injector for injecting a gaseous fuel is known, for example, from DE 10 2014 224 344 A1. The known gas injector, i.e., fuel injector, has an outwardly opening valve closing element and a flow guide element for forming a gas jet.

[0004] EP 4 047 199 A1 discloses a fuel supply device for supplying fuel to an internal combustion engine. A primary fuel is stored, and a secondary fuel, particularly in the form of molecular hydrogen, is generated in the vehicle by means of on-board reforming. In the internal combustion engine, the primary fuel and the secondary fuel are combusted in the same way, with the secondary fuel being supplied, in particular, as a pilot fuel.

[0005] DE 10 2013 220 479 A1 relates to an internal combustion engine that can be operated with liquid and gaseous fuel. In this case, direct injection is used to introduce gaseous fuel, while manifold injection is provided for introducing liquid fuel into the intake system of the internal combustion engine. Various injectors that enable both the injection of fuel and the injection of water into an internal combustion engine are known, for example, from documents DE 10 2017 005 162 A1 and DE 44 45 980 C2. An advantageous combustion process for gas engines, particularly using hydrogen as the fuel gas, should meet two important requirements.

[0006] Firstly, the combustion process should produce few pollutants and, in particular, only low nitrogen oxide emissions, which are formed by the Zeldovich mechanism when local combustion chamber temperatures are too high. To reduce these emissions, hydrogen engines are operated with a large excess of air, which increases the total heat capacity in the combustion chamber and distributes the heat of combustion over a larger mass. However, this air-diluted lean-burn combustion process requires good homogenization of the fuel in the air mass. If the fuel is inhomogeneously distributed, a high heat input occurs in areas of rich air-fuel mixtures on a locally smaller air mass. This locally increases the combustion chamber temperature to such an extent that more undesirable nitrogen oxides are formed. Good homogenization is therefore crucial for low pollutant formation.

[0007] Secondly, the combustion process should prevent pre-ignition. This can occur on hot components and prevents high mean effective pressures. Pre-ignition is an uncontrolled combustion abnormality that occurs before the regular ignition of the fuel-air mixture by the spark plug. These combustion abnormalities occur particularly at increased loads and especially near the spark plug or exhaust valve. Pre-ignition at high loads can be avoided by changing the type of mixture formation. Pre-ignition occurs in particularly fuel-rich mixtures that are subject to high local pressures and temperatures. Therefore, one preventative measure is to homogenize the fuel only shortly before ignition on the hot components and to avoid particularly fuel-rich mixtures in critical zones, such as under the combustion chamber roof.

[0008] To meet both requirements, the state of the art uses deflector caps to optimize the combustion process. These are thin-walled steel caps that are mounted over the injector tip and are provided with holes that create a specific spray profile. Configurations with central outlet holes in the injector's centerline and with lateral outlet holes are known.

[0009] A primary function of the spray-shaping caps is to prevent Coanda flow from the injector into the combustion chamber. This occurs when an outward-opening injector nozzle is mounted at the level of the combustion chamber roof with an excessively shallow seat angle. As a result, the flow exits parallel to the combustion chamber roof and forms a near-wall flow at the combustion chamber roof. This near-wall flow is detrimental to the combustion process, as it flows toward the still-hot spark plug and the hot exhaust valve at the combustion chamber roof, which can lead to uncontrollable pre-ignition.

[0010] A disadvantage of the jet-forming caps is their predetermined geometry, which cannot be dynamically adapted to different load conditions and thus allows only limited variability in the mixture formation.

[0011] Object of the invention

[0012] The invention is based on the object of providing a method for operating a gas engine that enables flexible combustion chamber filling. Furthermore, the object of the invention is to create such a gas engine.

[0013] The first sub-objective is achieved according to the invention by the methods according to claims 1 to 4. The methods can utilize a switchable fuel injector, as shown in the subsequently published DE 10 2023 121 667 A1. In the first setting, this enables a fuel gas flow spaced from the combustion chamber roof, and in a second setting, by utilizing the Coanda effect, generates a fuel gas flow adjacent to the combustion chamber roof. The second sub-objective is achieved by a gas engine according to claim 8.

[0014] The injector designed to supply the fuel gas, for example hydrogen, to the combustion chamber of the gas engine comprises a nozzle with a housing and a nozzle needle that can be moved within the housing. This nozzle needle comprises a shaft and an adjoining valve plate that widens towards the opening of the nozzle, so that an annular flow channel is formed between the nozzle needle and an inner wall of the housing, widening in the direction of hydrogen flow. This flow channel extends from a channel inlet at the transition between the shaft and the valve plate of the nozzle needle to the channel outlet at the end of the nozzle needle. The opening area of ​​the channel inlet is variable due to the displaceability of the nozzle needle, whereas the channel outlet at the end of the nozzle needle has a constant cross-sectional area across the entire adjustment range of the nozzle needle.

[0015] It has been shown that the design of the nozzle according to the application, including the nozzle needle which can be moved in its longitudinal direction, enables targeted switching between different flow states of the hydrogen to be injected into the combustion chamber of the internal combustion engine by means of direct injection.

[0016] The flow state of the hydrogen at the nozzle outlet depends on the setting of the nozzle needle, the pressure of the hydrogen at the channel inlet of the nozzle, and the backpressure in the combustion chamber, whereby it is assumed that the hydrogen is only fed into the combustion chamber after the intake valve has closed. Within the short time available for the supply of the gaseous fuel, the cross-sectional area of ​​the channel inlet can be changed by a longitudinal displacement of the nozzle needle in such a way that the flow changes direction within the nozzle after leaving the channel. A control cross-section is thus created at the channel inlet, i.e. at the narrowest gap in the nozzle. Overall, the nozzle is designed as a supersonic nozzle.

[0017] The transition between the various flow states occurs while maintaining a constant geometry at the port outlet, which, by definition, is located at the end of the nozzle needle. The sequential adjustment of various flow states during the injection process contributes significantly to the even distribution of the gaseous fuel in the combustion chamber. The selectively adjustable flow states can be considered hollow cone jets, which differ from one another in terms of their opening angle. One of the hollow cone jets can degenerate into a straight, practically non-fanning jet.

[0018] In general, the method for supplying hydrogen to a combustion chamber of an internal combustion engine designed as a reciprocating piston engine is characterized in that hydrogen is passed through a nozzle designed according to claim 1 and having a movable nozzle needle, wherein in a first setting of the nozzle needle, a hydrogen flow detached from the inner wall is generated after the valve plate of the nozzle needle, and in a second setting of the nozzle needle, at the corresponding point, a hydrogen flow is generated that rests against the inner wall of the nozzle in the sense of a Coanda flow. The flow state obtained in the second setting is particularly suitable for generating a widely fanned-out jet, whereas the separation of the flow in the first setting means that the hydrogen emerging from the nozzle flows into the combustion chamber of the engine in the form of a comparatively narrow jet.By repeatedly adjusting the nozzle needle during a piston stroke of the reciprocating piston engine, it is possible to switch repeatedly between the Coanda flow, i.e. a flow that is applied to a wall of the housing, and a flow that is not applied, particularly when the intake valves are closed.

[0019] The different spray shapes can be used to precisely direct the flow to hot components. For example, mixture formation at these critical points can be delayed until the end of the injection, making it much more controlled.

[0020] In contrast to a geometrically fixed spray cap with lateral holes, the disadvantage that these holes are open even at the beginning of injection, allowing fuel to flow toward the critical areas, is also eliminated. This can reduce the risk of pre-ignition. The spray cap must be applied to a specific operating point within the engine map. Parameters such as boost pressure, fuel pressure, valve timing, and the associated charge movement vary considerably. Compared to a spray cap, the invention utilizes the possibility of ensuring mixture formation at multiple operating points of the combustion engine by no longer linking the spray geometry to the spray cap geometry, but rather generating it variably through the injector.

[0021] The advantage of the proposed combustion process with an injector, which, depending on the setting, generates either a jet flow or a near-wall flow, is that the fuel can initially be injected with the central jet into a large, non-critical combustion chamber area with high kinetic energy and great penetration depth. This allows a large portion of the fuel to be homogenized as early as possible in the large, non-critical area, and subsequent homogenization can also take place in the critical areas, as the flow patterns now switch to a near-wall flow, which flows along the roof of the combustion chamber and transports the fuel specifically into the critical areas. Dosing is possible in a targeted manner, such as through transport with a macroscopic flow, such as a tumble flow.This allows the air-fuel ratio to be precisely adjusted even in critical zones, and the timing can also be adjusted as desired.

[0022] The near-wall flow is caused by the Coandæ effect, the extent of which in this case depends particularly on the shape of the injector's end piece. In general, this effect states that a flowing liquid or gas tends to flow along a curved surface. An injector designed using the Coandæ effect is known in principle, for example, from DE 10 2018 109 858 B4.

[0023] A further advantage of the process is that it also makes it easier to target the charge distribution, further optimizing the efficiency of the combustion process. For example, the mixture at the spark plug can be adjusted to be richer, which improves ignition and increases the combustion rate at the beginning of combustion, thus reducing knocking and enabling higher efficiency through faster fuel conversion. Furthermore, it is desirable to achieve less rich mixtures at the walls in order to reduce wall heat losses and the associated loss of efficiency.

[0024] Thus, in one embodiment of the invention, at low load, for example when the gas engine is idling or below a load threshold, the injector is operated in the second setting with a near-wall flow during the entire injection process.

[0025] In another embodiment of the invention, after a cold start of the gas engine or when a minimum temperature of a catalyst for the gas engine is undershot, the injector is operated in the second setting with a near-wall flow during the entire injection process.

[0026] Finally, a third embodiment of the invention provides for fuel gas to be injected into the combustion chamber upon a sudden load change after combustion, with the injector operating in the second setting during this injection process. A required increase in engine speed can thus be implemented more quickly.

[0027] The gas engine is preferably designed as a four-stroke engine, and the fuel gas is injected during the intake phase during partial load operation. During full load operation, the fuel gas is preferably injected during the compression phase.

[0028] In one embodiment, it can be provided that the intake valve is closed when the cylinder pressure reaches half the pressure of the rail.

[0029] The injector is suitable not only for use in a hydrogen injector, but also for use with other gaseous fuels, such as methane or ammonia. Regarding the actuators for adjusting the nozzle needle, proven solutions described in the prior art can be used. In addition to electromagnetic actuators, piezo actuators, for example, can also be used to actuate the nozzle needle of the fuel injector. An exemplary embodiment of the invention is explained in more detail below with reference to a drawing. These show:

[0030] Fig. 1 shows an injector for supplying hydrogen to a combustion chamber of an internal combustion engine in a first setting,

[0031] Fig. 2 the injector according to Fig. 1 in a second setting and

[0032] Fig. 3 is a control diagram of the injector according to Fig. 1.

[0033] An injector, designated overall by the reference numeral 1, is intended for use in a gas engine (not shown in detail) which is powered by hydrogen. In the present case, the gas engine is a reciprocating piston engine of a motor vehicle. Alternatively, the injector 1 could, for example, be an injector of a stationary gas engine in a combined heat and power plant. An actuator system of the injector 1, i.e. a fuel injector, is not shown. Figures 1 and 2 show a detail of a nozzle 2 of the hydrogen injector 1. Means upstream of the nozzle 2 for reducing the pressure of the hydrogen to be burned in the gas engine are not shown.

[0034] The fuel injector 1, i.e. gas injector, has a housing 3 which is only partially visible in Figures 1 to 3. A nozzle needle 5 is slidably guided in the housing 3, i.e. injector housing. A shaft of the nozzle needle 5 is designated 6, and a valve plate of the nozzle needle 5 is designated 7. Between the valve plate 7 and the inner wall of the housing 3, designated overall by 10, an annular flow channel 4 is formed which widens in the direction of flow of the hydrogen - in the arrangement according to Figures 1 to 3 from right to left. The narrowest point of the nozzle cross-section, at the transition between the shaft 6 and the valve plate 7 of the nozzle needle 5, is defined as the channel inlet 8. The channel outlet designated 9 is, by definition, located at the combustion chamber end of the valve plate 7, which is in the form of an end face 13 of the valve plate 7, which is also referred to as the end face.In this case, the end surface 13 has a flat shape, with the central axis of the shaft 6 representing a surface normal to the end surface 13. The diameter of the shaft 6 is designated d6. The diameter of the housing 3, shown in Fig. 1 and designated d3, does not necessarily represent a maximum dimension of the housing 3; rather, the diameter d3 refers exclusively to the illustrated section of the housing 3 having a cylindrical shape.

[0035] The valve plate 7 of the nozzle needle 5 has a curved surface section 11 and an adjoining cylindrical surface section 12, the latter extending, apart from any rounded edges, to the end surface 13. The diameter of the valve plate 12, designated d12, corresponds to the diameter of the cylindrical surface section 12 and, in the present case, is more than 1.5 times, but not more than four times, the diameter d6 of the shaft 6.

[0036] A plane located at the outlet end of the hydrogen injector 1, adjacent to the housing 3, represents a front plane 14. A distance a2_7 exists between this front plane 14 and the parallel end face 13 of the valve plate 7. The end face 13 is located within the interior space formed by the housing 3 in every setting of the hydrogen injector 1.

[0037] In its section projecting beyond the end face 13 and extending to the end plane 14, the housing 3 has a curved end section 15 which, as part of the inner wall 10, adjoins an outer cylindrical region 16 of the inner wall 10. At least one region of the cylindrical surface section 12 of the valve plate 7 bordering the end surface 13 is arranged concentrically within the outer cylindrical region 16 of the inner wall 10 in every setting of the nozzle needle 5, so that the geometry of the channel outlet 9 located on the valve plate 7 of the nozzle needle 5 is unchangeable. In the direction of the shaft 6, the outer cylindrical region 16 of the inner wall 10 merges into a concave wall section 18, to which a convex wall section 17 adjoins.The convex wall section 17, which is located in the area of ​​the channel inlet 8, is adjoined by an inner cylindrical region of the inner wall 10, designated 19. The diameter of the inner cylindrical region 19, designated d19, in the exemplary embodiment is at least one-third, but not more than 80%, of the diameter of the outer cylindrical region 16 of the inner wall 10, designated d16.

[0038] In the setting sketched in Fig. 1, the nozzle 2 is opened as wide as possible, i.e. the channel inlet 8 is set to the maximum cross-sectional area. The distance a2_7 is minimal in this setting. Compared to all other possible settings of the nozzle 2, the hydrogen flows at the channel outlet 9 at the highest velocity, where it is present as an under-expanded jet. The hydrogen jet expands towards the central axis of the nozzle 2, i.e. inwards, which is accompanied by a detachment of the jet from the inner wall 10 at the transition between the outer cylindrical region 16 and the end section 15. Hydrogen is thus introduced into the combustion chamber in the form of a narrow, at most slightly widening hollow jet, which emerges from the annular gap formed between the cylindrical surface section 12 of the valve plate 7 and the likewise cylindrical region 16 of the inner wall 10 of the housing 3.

[0039] If the flow cross-section at the channel inlet 8 is narrowed by retracting the nozzle needle 5, resulting in the setting shown in Fig. 2, a more extreme expansion ratio exists within the flow channel 4 compared to the setting shown in Fig. 1. This results in a lower static outlet pressure of the hydrogen at the channel outlet 9, which means that the flowing hydrogen has less of a tendency to expand towards the central axis of the nozzle 2. Instead, the hydrogen flow still rests against the inner wall 10 of the housing 3 even in the end region 15. This Coanda effect ensures that the hydrogen jet forms as a hollow cone jet with a large opening angle. The angle denoted by a, which is enclosed between a tangent applied to the curved end section 15 and the front plane 14, is 45° ± 15°.Even a slight defined axial movement of the nozzle needle 5 is sufficient to change the hydrogen flow from the separated flow set according to Fig. 1 to the Coanda flow forced in the setting according to Figure 2.

[0040] Figure 3 illustrates various possible flow conditions in a combustion chamber 21 of a gas engine, designated overall by 20, namely a multi-cylinder reciprocating piston internal combustion engine. A piston is designated by 22, and a spark plug by 23. Gas exchange valves of the internal combustion engine 20 are not shown.

[0041] The adjustable Coandæ flow is designated CS, and the similarly specifically adjustable flow, which is separated from the curved end section 15 and has the shape of a narrow hollow jet, is designated HS. The alternation between the various flows CS, HS depends, among other things, on the static pressure at the end of the nozzle 2. The static pressure here is the pressure of the flowing hydrogen acting on a surface parallel to the flow, in this case the inner wall 10. The flow designated CS within the combustion chamber 21 is not necessarily a flow that is completely designed as a Coandæ flow in the strict sense. In any case, the Coandæ flow CS within the nozzle 2 lies against its inner wall 10, particularly in the curved end section 15, which leads to the fact that - as idealized in Fig. 6 - the areas in the combustion chamber 21, particularly those close to the wall, are also filled with fuel gas.

[0042] If, however, the injector 1, including the nozzle 2, is operated in such a way that the fuel gas flow detaches from the wall in the end section 15, forming a relatively sharp hollow jet HS directed primarily toward the center of the combustion chamber 21, the pressure conditions are adjusted such that the static pressure of the fuel gas flowing out of the nozzle 2 is greater than the internal cylinder pressure acting in the combustion chamber 21. Figure 4 plots the pressure in the injector against the cylinder pressure. The fuel gas flow varies in the individual regions. The following different flow regions exist:

[0043] • Breiech I: Subsonic Coanda,

[0044] • Region II: overexpanding supersonic Coanda,

[0045] • Region III: under-expanding supersonic Coanda,

[0046] • Area IV: under-expanding free jet.

[0047] The flow patterns are familiar from gas dynamics. The Coandæ effect can thus occur in both the underexpanding and overexpanding regions.

[0048] The injector pressure is influenced by the fuel rail control as well as by gas-dynamic processes in the lines and in the individual reservoirs. It is conceivable that the pressure in the injector changes so drastically during the injection process that the flow pattern varies, even with the same cylinder pressure or one that changes due to the charge. One way to prevent these uncontrolled flow changes is to specifically pre-control this dynamic pressure. This can be achieved using a fast-acting valve arranged between a reservoir and the injection line. This adjusts the pressure so dynamically that the pressure at the injector changes only insignificantly, thus keeping the flow pattern constant.

[0049] Such an arrangement can be achieved, for example, by placing another injector upstream of a reservoir. This can be an identical injector, since the throughput per cylinder is limited due to the short injection time in direct injection mode. Across the entire crank angle range of 720 degrees, this creates the option of using the same valve as a fuel rail valve. This solution is suitable for three-cylinder, four-cylinder, or six-cylinder engines. Reducing the valve lift increases the geometric expansion ratio of the injector nozzle. The under-expanding areas are thereby gradually reduced until they ultimately disappear. This means that the free jet area becomes smaller and smaller until it disappears completely, and the injector can only function as a pure co-injector. The individual areas I - IV are therefore shifted towards the ordinate.

[0050] An increase in the Coanda radius leads to an increase in flow. This primarily results in the overexpanding region II growing at the expense of the underexpanding region III. Likewise, the free jet (region IV) is restricted at the same cylinder pressure. The regions of the Coanda effect are thus shifted overall toward lower cylinder pressures.

[0051] Part of the operation of a direct-injection combustion engine is carried out with the intake valve open. The strong charge movement of the air introduced via the intake valves generally leads to better homogenization. This is especially the case at low loads and high engine speeds. In this range, hydrogen is therefore injected into the combustion chamber with the intake valve open to achieve the highest possible homogeneity. At the same time, the risk of a flame flashing back into the intake manifold is significantly reduced. Disadvantages in intermediate pressure do not arise because the load requirement is low and, at the same time, the high flow rate can provide sufficient exhaust power for the turbine and thus the compressor.

[0052] In contrast, the operating range with relatively high engine loads and low engine speeds presents different requirements. Here, it is important that the turbocharger, which already has insufficient exhaust performance at low engine speeds, can bring as much air as possible into the combustion chamber. Additional recompression of the hydrogen is not helpful here. Direct blowout operation is therefore necessary. At the same time, the probability of flame flashbacks in the gas exchange area increases in this range. At early injection times and under free jet conditions, a particularly large amount of fuel gas can be introduced into the combustion chamber. With early injection and under co-addition flow, pre-ignition can be avoided and, under certain boundary conditions, the cooling effect of the injection jet on potential hotspots can be utilized.

[0053] Later intake timing increases the efficiency of the gas engine. This is achieved because the piston no longer has to recompress the fuel gas introduced at earlier intake times. At the same time, knocking is reduced by shortening the time required for pre-reactions, since the later intake timing also shortens the time interval to ignition.

[0054] The proposed processes are particularly suitable for stratified operation. By carefully controlling the spray shape between the free jet and the Coandè flow, various stratifications can be created. For example, the upper area of ​​the combustion chamber can be filled with fuel gas via the Coandè effect, while the lower area of ​​the combustion chamber remains predominantly fuel-poor. This results in the upper area burning through correspondingly quickly during normal operation, while the lower area is not used by the flame.

[0055] This circumvents the problem that occurs in hydrogen combustion engines, where high-pressure efficiency is insufficient due to the slow combustion of the mixture. This stratification still allows the mixture to burn quickly, yet the overall mixture is still lean, thus avoiding intake air throttling and its associated disadvantages.

[0056] Exhaust aftertreatment can also be improved with a pure coanda flow. Late injection points with a coanda flow can even be ignited by the spark plug while the exhaust gas is being expelled. Heat losses caused by possible afterburning can be avoided. The relatively small zone in which the flame is ignited by the spark plug no longer wets the entire combustion chamber. This leads to smaller heat losses and thus to a higher exhaust enthalpy, which benefits the substrate.

[0057] List of reference symbols

[0058] 1 injector

[0059] 2 nozzles

[0060] 3 housings

[0061] 4 flow channel

[0062] 5 nozzle needle

[0063] 6 shaft

[0064] 7 valve plates

[0065] 8 Canal entry

[0066] 9 Channel outlet

[0067] 10 Inner wall of the housing

[0068] 11 curved surface section of the valve plate

[0069] 12 cylindrical surface section of the valve plate

[0070] 13 Front face of the valve plate

[0071] 14 Front plane at the opening of the housing

[0072] 15 curved end section of the housing

[0073] 16 outer cylindrical area of ​​the inner wall

[0074] 17 convex wall section

[0075] 18 concave wall section

[0076] 19 Wall section, inner cylindrical area of ​​the inner wall

[0077] 20 gas engine

[0078] 21 Combustion chamber

[0079] 22 pistons

[0080] 23 Spark plug a Angle a2_7 Distance between the face of the valve plate and the housing face plane

[0081] CS Coanda current

[0082] HS separated flow, narrow hollow jet d3 diameter of the housing d6 diameter of the shaft d16 diameter of the cylindrical section 16 d19 diameter of the cylindrical section 19 d12 diameter of the valve disc

Claims

Patent claims 1 . Method for operating a gas engine (20) with - a cylinder having a combustion chamber (21) enclosed by a cylinder jacket, a combustion chamber roof and a cylinder base, - an inlet valve and an outlet valve as gas exchange valves and - an injector (1) for injecting fuel gas into the combustion chamber, wherein the injector (1) generates a fuel gas flow (HS) spaced from the combustion chamber roof in a first setting and a fuel gas flow (CS) adjacent to the combustion chamber roof in a second setting, characterized in that the injector (1) is operated in the first setting at the start of the fuel gas injection process and is operated in the second setting at the end of the injection process.

2. Method according to the preamble of claim 1, characterized in that when the gas engine (20) is idling or below a limit speed of the gas engine (20), the injector (1) is operated in the second setting during the entire injection process.

3. Method according to the preamble of claim 1, characterized in that after a cold start of the gas engine (20) or when a minimum temperature of a catalyst for the gas engine (20) is undershot, the injector (1) is operated in the second setting during the entire injection process.

4. Method according to claim 1, characterized in that the gas engine (20) is designed as a four-stroke engine and in partial load operation the fuel gas is blown in during the intake phase.

5. Method according to claim 1, characterized in that the gas engine (20) is designed as a four-stroke engine and in full-load operation the fuel gas is injected in the compression phase.

6. Method according to one of the preceding claims, characterized in that the dynamic pressure of the fuel gas is pre-controlled by a further injector connected upstream of the injector (1).

7. Gas engine (20) with a cylinder which has a combustion chamber (21) enclosed by a cylinder jacket, a combustion chamber roof and a cylinder base, with an inlet valve and an outlet valve as gas exchange valves and with an injector (1) for blowing fuel gas into the combustion chamber, wherein the injector (1) in a first setting generates a fuel gas flow (HS) spaced from the combustion chamber roof and in a second setting generates a fuel gas flow (CS) adjacent to the combustion chamber roof, characterized in that a further injector is connected upstream of the injector (1).

8. Gas engine (20) according to claim 7, characterized in that the further injector is identical in construction to the injector (1).

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