Method and control unit for controlling a turbocharged hydrogen engine

Abstract

The invention relates to a method for controlling a turbocharged hydrogen engine for burning an air-hydrogen mixture having an air-hydrogen ratio  greater than 1, wherein the hydrogen engine is adapted to assume steady-state operating conditions and transient operating conditions, wherein ignition timings in the transient operating conditions are adjusted later than in the steady-state operating conditions.

Description

[0001] Description

[0002] Title:

[0003] Method and control unit for controlling a turbocharged hydrogen engine

[0004] The present invention relates to a method and a control unit for controlling a turbocharged hydrogen engine.

[0005] State of the art

[0006] Hydrogen potentially offers CO2-free energy for mobile and stationary applications. In addition to fuel cells, internal combustion engines using hydrogen as fuel are also known, offering advantages for certain market segments, such as greater robustness in off-highway applications. Furthermore, they utilize established technologies, resulting in lower manufacturing and maintenance costs.

[0007] To ensure combustion stability in hydrogen engines while simultaneously limiting nitrogen oxide emissions, it is advisable to operate hydrogen engines in lean-burn mode, i.e., with a high excess air. The excess air ratio chosen for this purpose is ideally 2 or greater. Only a portion of the fresh air participates in combustion, which can lead to losses in steady-state power density and dynamic torque buildup. The hydrogen engine therefore responds to the torque demand only with a delay, especially compared to the torque buildup of a modern diesel or gasoline engine. Disclosure of the Invention

[0008] It is an object of the invention to propose a method and / or a control for a hydrogen engine to provide improved response behavior.

[0009] This object is achieved by a method for controlling a turbocharged hydrogen engine having the features of independent claim 1. Advantageous embodiments and further developments can be found in the subclaims and the following description.

[0010] A method is proposed for controlling a turbocharged hydrogen engine for burning an air-hydrogen mixture with an air-hydrogen ratio X greater than 1, wherein the hydrogen engine is designed to assume stationary operating states and transient operating states, wherein ignition points in the transient operating states are adjusted later than in the stationary operating states.

[0011] The hydrogen engine in question has one or more cylinders arranged in a desired manner in an engine block. An axially movable piston is arranged in each cylinder and is moved by a hydrogen-air mixture that is compressed and ignited in a chamber defined by the piston. The ignition point at which an ignition spark is triggered at a spark plug is dependent on the position of the piston and generally depends on the flame propagation speed and various operating and environmental parameters of the hydrogen engine. It is common practice to advance the ignition point with increasing engine speed, i.e., to points close to top dead center.

[0012] It is common practice to adjust the ignition timing for each operating condition of the hydrogen engine to ensure optimal efficiency. This could include, among other things, an evaluation of the so-called MFB50 (“Mass Fraction Burned”) point, at which half of the hydrogen has been burned. The ignition timing can be adjusted within certain limits to optimize combustion in a current operating condition and to avoid both knocking and backfiring. At full load, for example, knocking could occur if the ignition timing is too advanced, while backfiring is more likely to occur if the ignition timing is too late. This can be used to define a type of ignition timing range within which the ignition timing should fall. The ignition timing range can depend on the load and tends to be earlier at partial load than at full load.

[0013] During measurements on an engine test bench, it was surprisingly discovered that retarding the ignition timing in hydrogen engines offers advantages in terms of nitrogen oxide emissions and combustion stability. This allows the intended excess air to be reduced. This allows a larger amount of hydrogen to be temporarily converted into heat. Furthermore, such retarding of the ignition timing generally results in a higher proportion of the energy released by combustion remaining in the exhaust gas flowing from the hydrogen engine. The resulting increase in exhaust gas enthalpy can improve the response of the turbocharger arranged in the exhaust path, and consequently of the coupled compressor for increasing the air mass flow, and thus the overall torque buildup of the engine.

[0014] Consequently, the method according to the invention can significantly improve transient operating conditions, and the hydrogen engine controlled by this method can be operated much more dynamically, achieving full-load operation more quickly. This is achieved very cost-effectively according to the invention, since virtually no modifications to the hydrogen engine are necessary.

[0015] Alternatives to improving the responsiveness of a hydrogen engine can include alternative combustion strategies and measures to increase the gas mass in the cylinders. An alternative combustion strategy, for example, would be stoichiometric engine operation, which, however, is associated with a tendency to knock, particularly in the higher-load range, as mentioned above. Furthermore, fuel consumption is increased compared to lean-burn combustion processes. Measures to increase the gas mass in the cylinder can include, for example, electrical charging, assistance with a separate electric motor, air injection into an engine intake manifold, and other measures. However, these could significantly increase system complexity and manufacturing costs.

[0016] Retarding the ignition angle can temporarily lead to increased fuel consumption. However, since retarding is intended exclusively for transient and therefore non-stationary operating conditions in which increased torque demand is desired, this increased consumption is significantly limited overall. Once the desired boost pressure is reached in the hydrogen engine, the ignition angle can be shifted back to a range for optimal (mechanical) efficiency.

[0017] The air-to-hydrogen ratio X in steady-state operating conditions can be set to a higher value than in transient operating conditions. Consequently, the cylinders of the hydrogen engine can be filled significantly more intensively in transient operating conditions than in steady-state operating conditions. This results in increased exhaust gas enthalpy and, consequently, at least temporarily, improved turbocharger response to increase torque.

[0018] The air-to-hydrogen ratio X can be in a range of 2 to 4 in steady-state operating conditions and 2 or lower, preferably in a range of 1.7 to 2, in transient operating conditions. This achieves very high combustion stability and low nitrogen oxide emissions in steady-state operating conditions. In these conditions, the need for a rapid and significant torque increase is comparatively low, and the hydrogen engine operates less dynamically. However, this allows operation in a leaner range. In transient operating conditions, however, richer mixtures can be used, at least briefly. An air-to-hydrogen ratio below approximately 1.5 to 1.7 should be avoided, however, to further reduce the risk of uncontrolled combustion. It might be advisable to limit the air-to-hydrogen ratio to, for example, 1.7.The ignition timing during transient operating conditions could be in a range of 20° to 45°, preferably in a range of 38° to 42°, after top dead center. The flame propagation speed of hydrogen is significantly higher than that of gasoline or diesel, so the ignition timing can be significantly after top dead center. The later the ignition timing, the more the cylinder can be charged with an air-hydrogen mixture. Therefore, in transient operating conditions, when a higher torque increase is required, it may be advisable to adjust the ignition timing by up to 45° after top dead center.

[0019] The ignition timing could be set in a range of 0° to 25°, preferably 5° to 20°, after top dead center during steady-state operation. This achieves optimal combustion with low nitrogen oxide formation.

[0020] The ignition timing could be retarded in transient operating conditions with increasing torque increase. Consequently, the greater the required torque increase, the later the ignition timing could be. This would allow the exhaust gas enthalpy to be increased as needed to improve the response of the turbocharger and thus of a compressor coupled to the turbocharger to increase the air mass flow, while during steady-state phases it could be generated in a way that optimizes consumption and emissions. It would be conceivable to convert a torque increase request linearly into an ignition timing adjustment. It is also conceivable to implement this relationship exclusively for torque increase requests that lie in a range of 25% to 100%, and preferably 50% to 100%, of a theoretical maximum torque increase request.Furthermore, it is conceivable to retard the ignition timing accordingly only once a threshold value for a desired torque increase has been reached.

[0021] The ignition timing could also be adjusted back to the steady-state operating range when a predetermined pressure is reached at a compressor coupled to the hydrogen engine's turbocharger. Since the measure to improve response is only necessary during transient operating conditions, the ignition timing can be adjusted back to the optimal range immediately when the desired boost pressure is reached. Efficiency is then restored to the optimal range.

[0022] The air-to-hydrogen ratio X during transient operating conditions could be reduced by increasing the amount of hydrogen injected into the hydrogen engine. This increases the exhaust gas enthalpy, and the turbocharger is subjected to significantly greater mechanical stress for a short time. Due to the inertia of the turbocharger and compressor combination, the air mass flow for combustion initially remains largely constant or initially increases only slightly.

[0023] The invention further relates to a control unit for controlling a turbocharged hydrogen engine for burning an air-hydrogen mixture, wherein the control unit is designed to carry out the method described above.

[0024] Finally, the invention relates to a hydrogen engine comprising at least one cylinder, a turbocharger, a compressor, and the aforementioned control unit. This control unit is operatively coupled to the components of the hydrogen engine and is designed to regulate the operation of the hydrogen engine.

[0025] Further measures improving the invention are presented in more detail below together with the description of the preferred embodiments of the invention with reference to figures.

[0026] drawing

[0027] Figure 1 shows a schematic, block-based representation of a hydrogen engine and

[0028] Figures 2a and 2bCombustion and torque diagrams.

[0029] Description of the embodiments

[0030] Fig. 1 shows a hydrogen engine 2 having several cylinders 6 in which an air-hydrogen mixture is ignited by spark plugs 4. The hydrogen engine has an air inlet 8 and a hydrogen inlet 10. A turbocharger 12 is provided, through which exhaust gas flows, exiting from an exhaust outlet 14. The turbocharger 12 is coupled to a compressor 13, which compresses air and delivers air into the air inlet 8. The illustration here is very schematic and can be supplemented by conventional line and valve arrangements.

[0031] A control unit 16 is coupled to the hydrogen engine 2 and can, among other things, initiate the ignition of the spark plugs 4, wherein the ignition is generally correlated with the rotational angle of an engine shaft (not shown). Several sensors are provided, not shown here, which enable the control unit 16 to detect a current operating state of the hydrogen engine 2. These could be, for example, temperature, pressure, and mass flow sensors, which can be arranged at different locations on the hydrogen engine 2.

[0032] The control unit 16 is designed to carry out a method for controlling the hydrogen engine 2 to combust an air-hydrogen mixture with an air-hydrogen ratio X greater than 1, wherein the hydrogen engine 2 is designed to assume stationary operating states and transient operating states. The control unit 16 is designed such that ignition times are later in transient operating states than in stationary operating states. The turbocharger 12 can then be subjected to a significantly greater exhaust gas enthalpy and support the torque build-up of the hydrogen engine 2 by accelerating the compressor 13 more strongly. The ignition times can be adjusted up to a maximum of approximately 40° - 45° after top dead center (TDC) if more dynamic response is required. If the desired torque build-up by the hydrogen engine 2 has at least approximately occurred, orIf a desired pressure is applied to the compressor 13, the ignition timing can be shifted back into the optimal range, ie back towards the top dead center.

[0033] The air-hydrogen ratio X is set to a higher value in the steady-state operating conditions than in the transient operating conditions, approximately in a range from 3 to 4. In the transient operating conditions, however, the air-hydrogen ratio is below 3, preferably in a range from 2 to 2.5. This can be achieved in particular by temporarily filling the cylinders 6 with more hydrogen.

[0034] Fig. 2a and 2b show two diagrams illustrating the optimization of combustion in the hydrogen engine 2.

[0035] In a first diagram in Fig. 2a, various operating points of internal combustion engines are plotted as a function of the air-fuel ratio X on the vertical axis and the ignition timing in degrees after top dead center (TDC) on the horizontal axis. For comparison with the hydrogen engine 2, a first operating point 18, a second operating point 20, and a third operating point 22 of a diesel engine are shown with a dash-dotted line. The first operating point 18 is at an air-fuel ratio X of over 4 and corresponds to partial load operation. Full load operation, on the other hand, is represented by the third operating point 22. The second operating point 20 is passed through on the way to the third operating point 22. When the diesel engine quickly builds up torque, initially only one injection system reacts because the air-supplying system is too sluggish to immediately build up a higher air mass flow.The second operating point 20 passed through during this process can be at the engine's smoke limit. The second operating point 20 is transient, while the first operating point 18 and the third operating point 22 are stationary. At the third operating point 22, a boost pressure is sufficient to introduce a larger air mass flow into the engine. Ignition timing is continuously retarded during the transition from the first operating point 18 to the third operating point 22.

[0036] A conventional hydrogen engine is controlled in a similar way. Analogous to the diesel engine, three operating states 24, 26, and 28 are shown, corresponding to partial load operation, a transient condition, and full load operation. The ignition timing is continuously retarded. The air-to-hydrogen ratio X decreases from approximately 4 to slightly over 2. The progression between these three operating states 24, 26, and 28 is shown with solid lines.

[0037] The control according to the invention is indicated by the dashed line. Here, the first operating state 24, a second operating state 30 and the third operating state 26 are assumed one after the other. In contrast to the second operating state of the conventional hydrogen engine, the second operating point 30 in the control according to the invention is at a significantly different location in the diagram in Fig. 2a. Here, the ignition point is retarded significantly beyond the ignition point of the third operating state 28, so that the ignition point in the transient operating state is significantly higher than in the steady-state operating states 24 and 28. This allows the exhaust gas enthalpy to be significantly increased and the boost pressure to be built up more quickly, so that a stronger air mass flow can be built up in the shortest possible time. For example, the ignition point in the second operating state 30 is approximately 40° after top dead center, whereas in full-load operation, i.e.in the third operating state 28, at about 20° after TDC.

[0038] The operating limits of hydrogen engine 2 are delimited by hatched areas. The air-hydrogen ratio X can be approximately between 2 and 4 at earlier ignition timings, with these limits decreasing slightly with later ignition timings and ranging between approximately 1.5 and 3.5 at ignition timings approximately 40° after top dead center.

[0039] Fig. 2b shows the corresponding curves of the torque T of the conventional hydrogen engine and the hydrogen engine 2 controlled according to the invention in a diagram. Here, the torque in the second operating state 30 of the hydrogen engine 2 controlled according to the invention is significantly higher than the torque of the conventionally controlled hydrogen engine in its second operating state 26, so that the third operating state 28 is reached significantly faster in the hydrogen engine 2 controlled according to the invention than in the conventionally controlled

[0040] Hydrogen engine. The increase in dynamics is indicated by the time difference Δt.

Claims

Claims 1. Method for controlling a turbocharged hydrogen engine (2) for burning an air-hydrogen mixture with an air-hydrogen ratio X greater than 1, wherein the hydrogen engine (2) is configured to assume steady-state operating conditions and transient operating conditions, and wherein ignition timings are advanced later in the transient operating conditions than in the steady-state operating conditions.

2. The method of claim 1, wherein the air-hydrogen ratio X is set to a larger value in the steady-state operating conditions than in the transient operating conditions.

3. Method according to claim 1 or 2, wherein the air-hydrogen ratio X is in a range of 2 to 4 in the steady-state operating conditions and is 2 or lower in the transient operating conditions, preferably in a range of 1.7 to 2.

4. Method according to claim one of the preceding claims, wherein the ignition timings in the transient operating states are in a The range is from 30° to 45° and preferably from 38° to 42° after top dead center.

5. Method according to claim one of the preceding claims, wherein the ignition times in the steady-state operating conditions are determined in a The range is from 0° to 25°, preferably in a range of 5° to 20° after top dead center.

6. Method according to any one of the preceding claims, where the ignition timing is retarded in transient operating conditions as the torque increases.

7. Method according to one of the preceding claims, wherein the ignition timings are adjusted back to the range of steady operating conditions when a predetermined pressure is reached at a compressor coupled to the turbocharger (12) of the hydrogen engine (2).

8. Method according to claim 2, wherein the air-hydrogen ratio X is reduced in the transient operating conditions by increasing the amount of hydrogen injected into the hydrogen engine (2).

9. Control unit (16) for controlling a turbocharged hydrogen engine (2) for burning an air-hydrogen mixture, wherein the control unit (16) is configured to perform the method according to any one of claims 1 to 8.

10. Hydrogen engine (2) comprising at least one cylinder (6), a turbocharger (12), a compressor (13) and a control unit (16) according to claim 9.

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