Hydrogen combustion engine torque control

Abstract

Title: Hydrogen combustion engine torque control Abstract A hydrogen combustion engine comprising a plurality of combustion chambers each comprising a hydrogen fuel supply and a fuel ignition device, for converting the ignited hydrogen fuel to work, the engine further comprising an air intake manifold and an exhaust, a turbine for driving a turbocompressor; and an air intake throttle valve for closing off the air intake manifold from the turbocompressor, and an engine controller, wherein the engine controller is arranged to control the air intake throttle valve in accordance with a torque request T and corresponding fuel supply S to the combustion chamber; wherein, in a negative torque transient T’ that exceeds a threshold value, the controller is arranged to limit a fuel supply S to a fraction S’ of the plurality of combustion chambers to keep the air to fuel ratio within a combustible range during a transient period of closing the intake valve, and wherein said fraction S’ of combustion chambers receives a fuel quantity s’ that is correspondingly increased relative to the fraction s that would normally be provided to all of the plurality of combustion chambers.

Description

Title: Hydrogen combustion engine torque control FIELD OF INVENTION The invention relates to a hydrogen combustion engine and a method of controlling thereof. One alternative for a C02 free powertrain is a leanburn spark ignited H2-ICE (internal combustion engine) as this combines zero C02 capability with good efficiency. To maximize efficiency and power turbocharging the hydrogen combustion engine is a preferred option. DESCRIPTION OFTHE PRIORART In hydrogen engines, an intake throttle valve may close offthe air intake manifold and bring it into accordance with the fuel supply so that a desired air fuel ratio is achieved. It is important to limit engine conditions where air fuel ratios are in regions above 4, where an excessively high air-fuel ratio may render the ignition ofhydrogen fuel unstable. Optimum air fuel ratios for hydrogen combustion are in a range between 1.5-6, wherein a too low air fuel ratiomay lead to increasedNOx generation, and a too high air fuel ratiomay lead to combustion instability. The intake throttle valve to this effect controls the amount offresh air intake. To suitably adjust the amount of air ow in case of a sudden decrease of fuel supply, e.g. when the driver decelerates and the engine returns to an idle condition, itmay be adequate to close offthe intake throttle valve in a rapid fashion to avoid combustion instability and hydrogen slip in the exhaust. The intake throttle valve or ITV is thus a restriction that operates to be able to rapidly control an air fuel ratio during a negative transient torque variation, by severely limiting the amount of air ow. However, such a sudden decrease of air ow may result in a compressor surge event, which is causedby a prolonged pressure due to the interruption ofthe inlet ow. This may result in noise vibration harshness effects potentially damaging of the compressor fan blades or cause other mechanical integrity issue. On the other hand, a slower closing ofthe intake throttle valve will keep the air-fuel ratio high for a period oftime, increasing the chance ofcombustion instability. lt is therefore beneficial to close the intake throttle as soon as possible without causing compressor surge. While faster closing offthe intake throttle valve may thus solve this problem ofcombustion instability, during rapid negative transient torque variations, in particular: tip-outs (e.g. 100% to 10% load) the air ow from the turbocompressormay drop too rapidly leading to compressor surge ifno action is taken. Conventionally, e.g. on current diesel engines, anEGR valve may be opened to bypass the engine and have reverse EGR flow, to thereby increase the total ow away from the compressor and thus to prevent surge. For hydrogen application such a control method is not available since it could lead to combustion instability since the ITV causes a low pressure in the intake manifold relative to the exhaust manifold. Opening the EGR valve could lead to extraEGR and an even higher air fuel ratio. Another solution to prevent such a surge could be to add a compressor recirculation valve (CRV) that allows air to bypass the compressor to rapidly reduce boost pressure. However such a recirculation valve adds to costs and complexity, for which the invention seeks a solution. SUMMARYOFTHE INVENTION It is an object to provide a hydrogen combustion engine and a method of controlling thereofwherein during negative torque transients the engine is kept within combustible limits, while preventing compressor surge without adding additional compressor-by-pass hardware. To this end a hydrogen engine is proposed according to the features of claim 1. In particular a hydrogen combustion engine comprises a plurality of combustion chambers each comprising a hydrogen fuel supply and a fuel ignition device, for converting the ignited hydrogen fuel to work. The engine further comprises an air intake manifold; an exhaust, a turbine for driving a turbocompressor; an air intake throttle valve for closing offthe air intake manifold from the turbocompressor, and an engine controller. The engine controller is arranged to control the air intake throttle valve in accordance with a torque request T and corresponding fuel supply S to the combustion chamber; wherein, in a negative torque transient T that exceeds a threshold value, the controller is arranged to limit a fuel supply S to a fraction S of the plurality ofcombustion chambers during a transient period ofclosing the intake valve, and wherein said fraction S ofcombustion chambers receives a first fuel quantity s that is increased relative to a second fuel quantity s that is provided to all ofthe plurality ofcombustion chambers after the transient period. This operation enables a relative fast closing offof the intake throttle, so that the air-fuel ratio stays within an optimal combustion range. In the transient period wherein the torque request falls to a lower torque request, only a fraction of the combustion chambers or cylinders is fueled, wherein the rest ofthe cylinders operate to relieve the compressor ow, without causing a compressor surge or additional torque. This has the effect of a smoother decrease oftorque, without having a problem of too high air / fuel ratios, since the fuel supply for the remaining cylinders can be kept at a higher level to provide the requestedminimum torque. After the transient, fuel supply can be restored to all ofthe plurality ofcylinders at a fuel supply s, lower than the fuel supply s during the transient period. BRIEF DESCRIPTION OFTHE DRAWINGS The invention will be further elucidated in the figures: Figure 1 shows an embodiment ofan hydrogen internal combustion engine comprising an engine controller arranged to control the air intake throttle valve in accordance with a torque request; Figure 2 shows first time traces of the cycle C as depicted in Figures 8-5 ; Figures 8 - 5 show plot charts within a compressor mapM where cycles C are plotted ofopening and closing offthe air intake throttle valve. DETAILED DESCRIPTION Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understoodby one of ordinary skill in the art to which this disclosure belongs as read in the context of the description and drawings. lt will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context ofthe relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. In some instances, detailed descriptions ofwell-known devices and methods may be omitted so as not to obscure the description ofthe present systems and methods. Terminology used for describing particular embodiments is not intended to be limiting ofthe invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. The term "and / or" includes any and all combinations of one or more ofthe associated listed items. It will be further understood that the terms "comprises" and / or "comprising" specify the presence of stated features but do not preclude the presence or addition ofone or more other features. While example embodiments are shown for systems and methods, also alternative ways may be envisaged by those skilled in the art having the benefit of the present disclosure for achieving a similar function and result. E.g. some components may be combined or split up into one or more alternative components. Finally, these embodiments are intended to be merely illustrative ofthe present system and should not be construed as limiting the appended claims to any particular embodiment or group ofembodiments. Thus, while the present system has been described in particular detail with reference to specific exemplary embodiments thereof, it should also be appreciated that numerous modifications and alternative embodiments may be devisedby those having ordinary skill in the art without departing from the scope ofthe present systems as set forth in the claims that follow. The specification and drawings are accordingly to be regarded in an illustrative manner and are not intended to limit the scope ofthe appended claims. A controller, in particular, an engine controller arranged to vary the ignition timing ofan ignition device can be providedby circuitry or programming, by lookup tables or a combination thereof, by means known to the skilled person. Similarly, air and fuel supply can be controlled by controlling air inlet supply devices, controlling boost pressure by turbocompressor settings and additional air ow or fuel ow controllers or a combination thereof. Any reference signs in the claims do not limit their scope; several "means" may be representedby the same or different item(s) or implemented structure or function; any ofthe disclosed devices or portions thereofmay be combined together or separated into further portions unless specifically stated otherwise. The mere fact that certain measures are recited in mutually different claims does not indicate that a combination ofthese measures cannot be used to advantage. Turning now to Figure 1, there is illustrated an embodiment ofan hydrogen internal combustion engine 100. Ignition can be realized in any particular way, e.g. through a spark plug, a laser or prechamber, or compression ignition mechanism 140. The hydrogen engine may be of a type where the hydrogen is directly injected (DI) into the cylinder to mix with air before ignition, typically right after intake valve closing. The internal combustion engine 100 comprises an air intake 120, a fuel supply 180, and a fuel supply system 110. The fuel supply system 110 is arranged for supplying an amount ofhydrogen to the internal combustion engine. The air intake 120 is controlledby a turbo compressor 800. An intake throttle 122 may close offthe air intake 120. The internal combustion engine 100 further comprises an exhaust 200 for transporting the exhaust gas 201 from the internal combustion engine 100 through an engine after treatment system 210 (EAS), including selective catalytic reactor for removingNOX from the exhaust gases, to the environment. The internal combustion engine 100 further comprises an engine controller 500 arranged to control the ignition timing, air supply 120 and fuel supply 130, aimed at regulating the torque. This can be achieved through a combination ofignition timing, air and fuel supply. In particular the engine controller is arranged to control the air intake throttle valve in accordance with a torque requestT and corresponding fuel supply S to the combustion chamber; wherein, in a negative torque transient T that exceeds a threshold value, the controller is arranged to limit a fuel supply S to a fraction S ofthe plurality of combustion chambers to keep the air to fuel ratio within a combustible range during a transient period ofclosing the intake valve, and wherein said fraction S of combustion chambers receives a fuel quantity s that is increased relative to a fuel quantity s that is provided to all ofthe plurality ofcombustion chambers after the transient period. In Figure 2 time traces are shown of a cycle from a stationary (idle) conditionO to a torque demand T in phases a-b; whereas thereafter the engine returns to idle in phases c-d; also as depicted in Figures 3-5 that illustrate an exemplary embodiments ofcontrolling the engine as described. In trace I of Figure 2 phase O (between -2 and 0 seconds) corresponds to a fuel supply S during an initial time period with throttle valve closed or almost closed ranging from 0-7% (see trace II) and the engine is running at 1000 rpm; subsequent phase a corresponds to the air intake throttle valve being opened to 100%. In this phase a, trace III shows an increase between 0 and 4 seconds in torque T until a steady increased level is achieved in phase b (around 4 10 seconds), which is providedby increasing the injected fuel mass (trace I). Air fuel ratio is substantially constant at a level of about 2, which is far below a threshold ratio of about 4-6. In phase c, the air intake throttle valve is closed off; with a different timings indicated at iv in trace II, i.e. a fast timing for 6 cylinders (corresponding to compressor mapM Figure 8), a slow timing for 6 cylinders (corresponding to compressor map Figure 4) and a fast timing for 2 cylinders active (corresponding to for Figure 5). Turning to trace IV in Figure 2, it is apparent that the closing phase c of the intake throttle severely affects the cylinder mass ratio or air fuel ratio. Due to sudden closing ofintake throttle and drop ofinjected fuel mass (trace I) the fuel the air to fuel ratio rapidly goes to initial very high values, to return to moderate elevated values slowly thereafter. The aim is to limit the window where values are above 10 to as short as possible, and to achieve a condition where values are below 4 as early as possible. Three cases are illustrated in trace IV. Curves ii and iii correspond to a 6-cylinder fueling condition; curve i corresponds to a preferred case wherein the controller is arranged to limit fuel supply S to a fraction ofthe plurality of combustion chambers to keep the air to fuel ratio within a combustible range during a transient period c-d ofclosing the intake valve period. It can be seen that the smallest window ofproblematic air / fuel ratio is achieved by a fast closing curve i. In this curve air to fuel ratio is almost immediately restored to values below 8. The less favorable curve iii correspond to a slow closing ofthe throttle valve, which also results in a very slow decrease ofthe air to fuel ratio, due to continued presence of air mass ow. The second curve ii in trace IV corresponds to a fast closing ofthe throttle valve illustrated by the rapid drop in trace II. While a fast closing ofthe throttle may limit combustion instabilities, it is problematic for the compressor, as can be found in compressor mapM ofFigure 3 where the cycle O-a-b-c-d is depicted. It is found that a fast closing of the intake throttle for 6 active cylinders can be problematic in region P where a closing phase c-d of a cycle C achieves pressure ratios for the compressor that are too high for the corresponding low mass ow rate at that point. This may result in integrity issues for the compressor, e.g. blades may be damaged. Generally, the aim is to limit the pressure / ow conditions inside an operative region of the compressor, that is indicated by a compressor map M that provides an operative region in a domain ofpressure ratio versus a corrected mass ow rate, as is known in the art. Such a compressor mapM may deviate for specific types ofcompressor layouts, but generally aims to limit pressure ratios between inlet and outlet ofthe compressor in lower ow rate areas of the compressor operation. ln phase d, the transient state finishes and a steady state oflow torque request is achieved resuming to O. In Figure 4, with a cycle is presented corresponding to a slower closing of the intake throttle in the transient phase c-d corresponding to curve iv in Trace II of Figure 2. As expected, in this condition, cycle C is executed within the boundaries ofthe compressor mapM e.g. with the closing ofthe throttle valve delayed. The exemplary slower closing ofthe ITV in the curve iv region has a fast initial drop c to an initial semi-closed position, but is delayed in closing in phase d to a timing larger than 0.4 seconds, preferably with a timingbetween 0.6 and 1.5 seconds, more preferably with a timingbetween 0.9 and 1.1 second. The semi- closed position may be such that it is kept about 10-80% open to prevent compressor surge events. While an initial fast drop already somewhat limits the period of increased air-fuel ratio to values above 10, compared curve ii in Trace IIII this slower closing leads to undesired air fuel ratios substantially above 6-10, for periods larger than about 0.5-1 seconds. In Figure 5 the compressor map conditions are illustrated to be similar to the Figure 4 conditions, butnow the engine is kept fueled over a longer period of time (e.g. about 1-3 seconds) to reach an idle condition, with a limited amount of cylinders. In particular (see trace I curve v ofFigure 2), a fuel supply S is continued with an increased fuel quantity s that is correspondingly increased relative to the fraction s that would normally be provided to all ofthe plurality ofcombustion chambers. Possible cylinder fractions may be, for a six cylinder engine at least one, but more realistically 2, 3, ofeven 4 or 5 ofthe cylinders running at a fuel quantity s that is increased relative to a second fuel quantity s that is provided to all ofthe plurality ofcombustion chambers after the transient period, in particular in idle condition. ln conclusion, as can be seen in Figure 5, the air intake closing cycle c-d can be kept within the combustible range, leading to a smoother air intake throttling, and at the same time leading to a better controlled negative transient torque control ofthe hydrogen engine.

Claims

1. A hydrogen combustion engine comprising: a number of combustion chambers, each with a hydrogen fuel supply and a fuel ignition device, for converting the ignited hydrogen fuel in work, whereby the engine further comprises: an air intake manifold; an exhaust, a turbine for driving a turbocharger; an air intake throttle valve for closing off the turbocharger air intake manifold, and a motor controller, where the motor controller is configured to: to regulate the air intake throttle valve in accordance with a coupling request T and corresponding fuel supply S to the combustion chamber; where, with a negative torque transient T that a exceeds threshold value, the controller is configured to a fuel supply S limit to a fraction S of the combustion chambers during a transient period of closing of the intake valve, and where said fraction S of combustion chambers receives an initial quantity of fuel s that is increased with respect to a second fuel quantity s that to all combustion chambers are delivered after the transient period.

2. The hydrogen combustion engine according to one of the preceding conclusions, where the second quantity is a fuel quantity for engine operation at low load.

3. The hydrogen combustion engine according to one of the preceding conclusions, where the said fraction S is 2 / 6, 8 / 6, or 4 / 6 in a 6-cylinder engine.

4. The hydrogen combustion engine according to one of the preceding conclusions, whereby the air intake throttle valve is closed from an open to an Semi-closed position within 0.1 0.5 seconds.

5. The hydrogen combustion engine under the preceding conclusion, whereby the air intake throttle valve is preferably closed within 0.3-0.4 seconds.

6. The hydrogen combustion engine according to one of the preceding conclusions, where the air intake throttle valve is closed from a half-closed to a fully closed position within 1.0-1.5 seconds, where the half-closed position is at least 10% open.

7. A hydrogen combustion engine according to one of the preceding conclusions, where there is a single airflow path between the turbocharger and the air intake manifold.

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