Method of controlling hydrogen internal combustion engine

Abstract

The invention relates to a method of operating a hydrogen internal combustion engine in which a combustion event is operated by injecting a predetermined amount of fuel QF in at least one cylinder, the method comprising the steps of: determining a fuel demand QD as a function of an input torque demand TD; determining a corresponding desired air mass MD based on the fuel demand QD and a standard lambda number LSTD, and adjusting at least one charge air parameter based on the desired air mass MD; and determining a predetermined fuel quantity QF based on the current (intake) airflow MF rate and a lambda setpoint LSET corresponding to the standard lambda number LSTD. In the event of a change in torque demand, a Lambda setpoint LSET is set to a Lambda value referred to as fast Lambda LFAST, where LFAST is a Lambda number calculated based on the current air flow MF and the current fuel demand QD.

Description

Technical Field

[0001] The present invention relates generally to spark-ignition internal combustion engines and, more particularly, to combustion control in hydrogen engines. Background Art

[0002] For automotive applications, hydrogen engines are considered a promising alternative to gasoline or diesel engines because the emissions of hydrogen engines consist mainly of water.

[0003] Today, hydrogen fuel engines are developed / designed primarily based on knowledge and technology from gasoline engines, with modifications and new developments as needed.

[0004] As is known, gasoline / gas operated engines are controlled based on an "air lead" approach, where lambda is primarily constant (stoichiometric), the air charge is adjusted according to the load, and the fuel is then calculated according to the fresh air flow to meet the lambda set point. This control of the air-fuel mixture is required for optimal operation of the catalytic converter.

[0005] One drawback of this conventional approach when applied to hydrogen combustion engines is the lag in torque response when the driver presses the accelerator pedal to request a rapid change in torque. This lag is due to a combination of elements: boost lag from the turbocharger running at low enthalpy (lean lambda set point); lambda demand depending on actual torque to achieve a consistent combustion set point (air / spark / injection timing demand).

[0006] Purpose of the Invention

[0007] It is an object of the present invention to provide a method of operating a hydrogen combustion engine which alleviates the above-mentioned disadvantages.

[0008] This object is achieved by a method for operating a hydrogen internal combustion engine as claimed in claim 1 . Summary of the invention

[0009] The invention relates to a method for operating a hydrogen internal combustion engine, wherein a predetermined fuel quantity Q is injected into at least one cylinder. F To operate the combustion event. Typically, the fuel quantity is determined for one engine cycle (ie, for all cylinders), and then the fuel quantity Q is distributed among the various engine cylinders for the corresponding cycle. F Therefore, Q F , or more precisely, the Q of the corresponding cylinder F The fraction is the value of the amount of fuel on which the fuel injector command (pulse width) is based. That is, the fuel injector is controlled so that during the engine cycle, the fuel corresponding to Q is injected into the engine. F of fuel.

[0010] In operation, according to the input torque demand TD Determine fuel demand Q D , and based on the fuel demand Q D and corresponds to the rare standard λ, i.e., L STD The predetermined λ set point determines the corresponding desired air quality M D Then based on the expected air quality M D Adjusting at least one charge air parameter. The term "charge air parameter" herein refers to a parameter that affects the amount of air entering the engine. For example, adjusting at least one charge air parameter may involve adjusting at least one of a throttle position and a variable valve of a turbocharger. Torque demand T D Represents the sum of the torque demands consisting of the driver torque demand (eg, directly via the accelerator pedal or indirectly via the cruise control) and the torque demands of other engine / vehicle components.

[0011] Standard λ is L STD is a predetermined value conventionally set for a lean air-fuel ratio under steady or quasi-steady operating conditions. In the case of a hydrogen engine, the standard λ, i.e., L STD The number can usually be between 1.8 and 3.

[0012] According to the present invention, when the torque demand T D In case of changes, λ set point L SET is set to be called fast lambda, i.e., L FAST The fast λ is L FAST is based on the current air flow M F and the current fuel demand Q D The number of lambdas to calculate.

[0013] Therefore, in the present method, when a change in torque demand is detected, a fast lambda strategy is applied, which uses lambda L FAST As the set point (L SET ), which deviates from the standard λ(L STD ).

[0014] For example, in the case of a strong torque demand, a richer lambda value is used to calculate the fuel quantity Q F A set point that deviates from the standard lambda calibrated for high efficiency and low NOx combustion.

[0015] Fast lambda allows departure from a strict "air lead" approach and allows the fuel change rate to be changed at a different rate than the "air" change rate during torque transient operation. This will reduce the time required to meet the power demand.

[0016] It should be noted that the present method differs significantly from conventional practice for gasoline engines, where lambda is essentially constant, charge air is adjusted according to load, and fuel is calculated strictly relative to the lambda set point according to actual air flow. Conventional gasoline engine controls are not designed to accommodate the range of lambda numbers allowed by hydrogen.

[0017] In contrast, the present method is applicable because the fuel is hydrogen: hydrogen engines have a precise combustion lambda authority that allows operation in a limited range of lambda values. For example, a hydrogen engine can be operated with lambda values ​​in the range of 1.8 to 3 (standard lambda).

[0018] The term lambda (or lambda number) is used herein to refer to the air-fuel ratio actually present in the combustion chamber compared to the stoichiometric air-fuel ratio. Typically, a lambda value of 1.0 corresponds to stoichiometric combustion conditions. The term lambda should generally be interpreted to include any parameter representing the stoichiometry of combustion, with varying scales or indices.

[0019] In the context of the present invention, the term "change in torque demand" refers to an increase or decrease in torque demand, resulting in a torque transient, which can be determined by any suitable method. For example, the change in required torque can be determined by comparing the torque difference (torque (t1)-torque (t0)) with a threshold or by comparing the torque ratio (rate of change of torque: torque (t1) / torque (t0)) with a threshold. Therefore, in the event that the torque difference (determined as a difference or ratio) between the current time point and the previous time point exceeds a predetermined threshold, it can be considered that there is a change in torque demand.

[0020] In particular, the rate of change of the torque demand may be determined by comparing the current torque demand with a reference torque demand. The reference torque demand may be a previous torque value. Alternatively, the reference torque demand may be a moving average of previous torque values.

[0021] In an embodiment, the fast λL FAST Represented by L FAST Relative to the standard λ value L STD The relative λ ratio R DEV to limit the limit.

[0022] In an embodiment, R DEV is calibrated and depends on the difference in torque demands. That is, the difference in torque demands can be entered in a map, which gives R DEV The difference in torque demand may be determined as the difference between the current torque value and the reference torque value, as described above (particularly where the reference is a moving average).

[0023] In doing so, L can be permanently calculated FAST , you can use R permanently DEVMap and apply it as L SET If the torque difference does not deviate from the standard λ value, then R DEV is set to 0, thereby allowing deviations from L STD , and therefore L FAST Set to standard L SET However, in the presence of a large torque difference, the mapped R DEV The value allowed is L STD to reduce the hysteresis effect.

[0024] For example, the relative λ ratio R DEV can vary between -30% and +30%. STD The difference is + / - 30%.

[0025] In an embodiment, L FAST It is further limited between a minimum lambda value Lmin and a maximum lambda value Lmax calibrated according to the engine speed and the engine load. For example, Lmin may be in the range of about 1.5 to 1.8; and Lmax may be in the range of about 2.2 to 3.5.

[0026] In an embodiment, the fuel demand Q is determined for each engine cycle. D , fuel quantity Q F (amount to be injected in all cylinders).

[0027] In an embodiment, when the difference in torque is low (quasi-zero) or zero, the lambda set point L SET is set (returned) to the standard lambda value (ie, the value corresponding to the steady state). BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The present invention will now be described by way of example with reference to the accompanying drawings, in which:

[0029] Figure 1 is a schematic diagram of a prior art engine management strategy;

[0030] Figure 2 is a schematic diagram showing an embodiment of the present method of operating an engine;

[0031] Figure 3 and Figure 4 It is shown that the use of Figure 1 A graph of the response of a prior art engine management strategy to a loading step;

[0032] Figure 5 and Figure 6 It shows the realization of Figure 2 A graph of the response of the loading step of the strategy of the present invention. DETAILED DESCRIPTION

[0033] As is well known, in gasoline engines, a throttle valve controls the air rate supplied to the engine in response to a vehicle operator's power demand, such that a fuel supply system supplies an amount of fuel based on the air supply rate to achieve a desired air / fuel ratio.

[0034] To reduce exhaust emissions, engines are usually equipped with a catalytic converter that converts NO 2 Reduction catalysts for the reduction of nitrogen and oxygen and the oxidation of CO to CO 2 and oxidizes HC into water and CO 2 The function of the oxidation catalyst.

[0035] For optimal operation of the catalytic converter, the spark ignition engine is operated under stoichiometric conditions, where the amount of oxygen supplied to the engine cylinders is the exact amount required to completely burn the amount of fuel supplied. In the case of gasoline, the stoichiometric air-fuel ratio is about 14.7:1, but the exact value depends on the fuel composition.

[0036] Figure 1 A conventional air-guided combustion management strategy for such a gasoline combustion engine is shown in FIG. Reference numeral 10 denotes a torque structure module that receives torque requests from various components, such as direct torque requests from the driver (accelerator pedal) or indirect torque requests via cruise control, torque requests from the transmission system, torque requests from driving dynamics, or torque requests related to specific components (catalytic converter, HVAC, etc.). The torque structure module 10 coordinates these various requests and generates a global torque request T D .

[0037] The desired fuel mass Q is then determined, typically by calculation based on IMEP (Indicated Mean Effective Pressure), cylinder volume and combustion efficiency coefficient D (also called fuel demand) to meet the desired torque demand T D At 12, based on the desired fuel mass Q D And consider the expected λ number L STD To calculate the expected air quality M D . Adjusts throttle and turbocharger valve positions based on desired air mass. Sets lambda number for stoichiometric combustion.

[0038] The fuel calculation module 14 determines the final fuel mass Q F , which is the amount of fuel injected into the engine (total fuel for all cylinders) for the upcoming combustion cycle and used for engine management strategies. Final fuel mass Q F Based on the fresh air flow M F And for a given λ set point L SETFor the benefit of the catalytic converter, the lambda set point is selected to obtain stoichiometric combustion, i.e., L SET =L STD =1.0.

[0039] As mentioned above, Figure 1 The combustion management strategy shown is now the basis for controlling hydrogen engines. When operating a hydrogen engine in the above scheme, the standard lambda number is usually calibrated for lean combustion to avoid NOx production. The standard lean lambda can be about L STD =2.7.

[0040] <The present invention>

[0041] Figure 2 The embodiment of the method of the present invention is shown. Figure 1 The conventional air induction management scheme shown is commonly used with gasoline engines.

[0042] The method is designed to account for transients due to torque changes and therefore works temporarily in this situation.

[0043] As mentioned above, under standard operation, you can use Figure 1 scheme to run hydrogen engines. STD Usually corresponds to a lean air / fuel ratio, such as L STD It may be in the range of 3 to 2.5, in particular about 2.7.

[0044] The present invention applies a strategy of using different lambda setpoints in case of varying torque demand. Roughly speaking, L STD The values ​​are calibrated to apply during steady-state engine conditions, where no increase or decrease in torque occurs. In this case, the torque demand difference (T D ) is considered to be quite low, including zero or quasi-zero.

[0045] In contrast, in the event that the driver depresses the pedal, or in the event of deceleration (ie in the event that the engine is no longer in steady-state operation), there is a torque demand difference (change) in the sense of the present method.

[0046] The change in torque demand can usually be obtained by changing the current torque demand (e.g., T D ) is determined by comparing it with a previous reference value of the torque demand.

[0047] In the case of a change in torque demand, it is called L FAST The different λ are used as set points L for the global fuel mass calculation 14 SET .

[0048] This comparison can be done, for example, by subtraction or by calculating a ratio, the result of which can then be compared with a threshold or used directly as an input in the mapping to affect the value L FAST (As will be explained below.) In an embodiment, the current torque request is compared to a moving average of the torque requests (for previous combustion cycles).

[0049] L FAST is the output value of module 16, which receives the current / actual air flow M F and the standard λ value L STD as input.

[0050] First, based on the expected fuel mass Q D and the actual air flow M F Calculate the so-called raw lambda, Lraw. Preferably, Lraw is calculated as:

[0051]

[0052] Where AFR stoichH2 The mass stoichiometric ratio of fuel to hydrogen is 34.33:1

[0053] Lraw is then processed to introduce two constraints:

[0054] i) Lraw is limited to a maximum deviation from a standard λ value.

[0055] Here, the value Lraw corresponds to the value relative to L STD The predetermined deviation ratio R DEV If Lraw exceeds the value applied to L STD The predetermined deviation ratio R DEV , Lraw is constrained (limited) to the maximum value.

[0056] For example, suppose R DEV is set to 15%. Then, in the case of acceleration, the maximum allowed value of Lraw is 0.85×L STD Then, in the case of deceleration, the maximum permissible value of Lraw is 1.15×L STD .

[0057] Predetermined deviation ratio R DEV Conveniently depends on the difference in torque requirements.

[0058] Therefore, in practice, R can be mapped according to the difference in torque demand DEV Therefore, R can be varied according to the magnitude of the difference in torque demand. DEV In addition, R DEV Set to zero to disable the LSTD where the difference in torque demand is zero or very small. Therefore, in practice L FAST can always be calculated, but is configured so that it cannot be obtained from L STD changes, where the difference in torque demand reflects steady-state operation.

[0059] ii) Lraw is further limited between minimum and maximum values ​​calibrated according to engine speed and load.

[0060] The idea here is to define a table that:

[0061] - In order to maintain acceptable combustion stability, there is a maximum limit Lmax to avoid too "lean" combustion;

[0062] -Having a lower limit Lmin to avoid too rich combustion to control NOx emissions and abnormal combustion;

[0063] Where Lmax and Lmin depend on engine speed and load.

[0064] Therefore, if Lraw is within the range [Lmin; Lmax], the value Lraw is used as a fast lambda value, i.e. as a set point. This can be written as L FAST =Lraw.

[0065] If Lraw exceeds Lmax, then L FAST The value of Lmax(L FAST =Lmax)

[0066] If Lraw is lower than Lmin, then L FAST The value of Lmin(L FAST =Lmin)

[0067] The value L thus determined in module 16 FAST It is then forwarded to module 14 where it is used as the lambda setpoint (L SET =L FAST ).

[0068] Figures 3 to 6 The effect of the present invention is shown, wherein Figure 3 and Figure 4 Corresponding to Figure 1 The conventional method of graph . Figure 5 and Figure 6 Involving the implementation of this method.

[0069] Figure 3 and Figure 5 The curves of IMEP and IMEP all show the torque demand reflected by the accelerator pedal position (here the loading step), the throttle position and the desired IMEP as a function of time. The desired IMEP reflects the torque demand TD .

[0070] Figure 4 and Figure 6 The corresponding changes of several combustion related parameters are shown: fuel demand Q D 、Fuel quantity Q F , L SET , and for Figure 6 , only fast λL FAST And contrast.

[0071] Reference Figure 3 and Figure 4 , Region 1 corresponds to steady-state operating conditions where it is useful to run as lean as possible to keep NOx emissions low and reduce pumping torque when possible.

[0072] In the graph, it can be seen that the torque increases rapidly as the throttle opens in section 2. In section 3, the torque increases slowly as the lambda setpoint decreases.

[0073] It can be observed that the conventional approach results in very long load transients because the lambda set point depends on the actual IMEP. This lag is due to a combination of: boost lag from the turbocharger running at low enthalpy (lean lambda set point); lambda demand depends on the actual torque to obtain a consistent combustion set point (air / spark / injection timing demand).

[0074] In this example, the time period to achieve the target 900 kPa IMEP is 3.5 seconds. This is considered unacceptable.

[0075] Go to Figure 5 and Figure 6 , a similar load step is requested again with a desired IMEP of 900 kP as load step.

[0076] It can be seen that the torque increases rapidly as the throttle opens. SET Compared with the standard λ set point L STD Concentration (15%). Figure 3 and Figure 4 The torque increases as the lambda setpoint decreases.

[0077] The time required to reach 900 kPa IMEP is 1.7 seconds here.

[0078] Therefore, the method of the present invention has the following benefits:

[0079] - Faster load transients can be achieved by using a method with lambda burning authority;

[0080] - When driver torque is reduced, there is no need to reduce spark efficiency, which is beneficial in terms of fuel economy.

Claims

1. A method for operating a hydrogen internal combustion engine, wherein a predetermined amount of fuel Q is injected into at least one cylinder F To operate a combustion event, the method comprises the following steps: According to the input torque requirement T D Determine fuel demand Q D ; Based on the fuel demand Q D and the standard lambda number L STD Determine the corresponding expected air quality M D , and based on the desired air quality M D adjusting at least one charge air parameter; as well as Based on the current (intake) air flow M F The rate and the standard lambda number L STD The λ set point L SET Determine the predetermined fuel quantity Q F ; It is characterized by that, in the case of a change in torque demand, the λ set point L SET is set to be called fast λL FAST The lambda value, Among them, L FAST is based on the current air flow M F and the current fuel demand Q D The number of lambdas to calculate.

2. The method according to claim 1, wherein: L FAST Represented by L FAST Relative to the standard λ value L STD The relative λ ratio R DEV to limit the limit.

3. The method according to claim 2, wherein: The relative λ ratio R DEV is calibrated and depends on the difference in torque demand.

4. The method according to claim 2, wherein: The relative λ ratio R DEV Between -30% and +30%.

5. The method according to claim 1, wherein: Fast λL FAST is further limited to a minimum lambda value L calibrated according to engine speed and engine load min and the maximum λ value L max between.

6. The method according to claim 5, wherein: L min in the range of about 1.5 to 1.8; and L max In the range of about 2.2 to 3.

5.

7. A method according to any one of the preceding claims, wherein: The fuel demand Q is determined for each engine cycle D , the fuel quantity Q F .

8. The method according to claim 1, wherein: When the difference in the torque demands is low, the lambda setpoint L SET is set back to the standard lambda value.

9. The method according to claim 1, wherein: A change in the torque demand is determined based on a rate of change of the torque demand.

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