Method for heating an engine pollution control catalyst
The method of stratified fuel injection and timed ignition during the expansion phase in a spark-ignition engine addresses the inefficiencies in catalyst heating by minimizing polluting gas emissions, maximizing gas temperature, and maintaining combustion stability, thereby improving the overall depollution process.
Patent Information
- Application Number
- FR2023012664
- Authority / Receiving Office
- FR · FR
- Patent Type
- Utility models
- Current Assignee / Owner
- Filing Date
- 2023-11-17
- Publication Date
- 2025-05-23
- Estimated Expiration
- 2033-11-17
AI Technical Summary
Existing methods for heating engine pollution control catalysts during the warm-up phase often result in increased nitrogen oxide emissions and combustion inefficiencies, which contradict the goal of minimizing polluting gas emissions.
A method involving a stratified fuel injection step starting between 0° and 90° crank angle after the piston passes its top dead center, followed by an ignition step beginning between 2 and 15° crankshaft angle after the end of the stratified injection, both occurring during the expansion phase to minimize emissions and maximize gas temperature while maintaining combustion stability.
This method effectively minimizes the emissions of polluting gases, maximizes the temperature of the gases, and maintains combustion stability similar to conventional triple injection, while reducing nitrogen oxide emissions and improving catalyst heating efficiency.
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Abstract
Description
Title of the invention: Method for heating an engine pollution control catalyst Technical field
[0001] The present invention relates to the minimization of polluting emissions from combustion engines.
[0002] In particular, the present invention relates to a method for injecting fuel into the cylinders of an engine for heating a pollution control catalyst of said engine, the heating enabling the improvement of the performance of treatment of the polluting molecules emitted in the combustion gases of said engine by said pollution control catalyst.
[0003] Generally speaking, the invention applies to any spark-ignition internal combustion engine, the pollution control catalyst being in particular a three-way catalyst. Previous techniques
[0004] One of the challenges facing the automotive industry is the depollution of internal combustion engines, particularly spark-ignition engines, operating for example with gasoline as fuel, whose depollution standards impose increasingly lower thresholds for polluting gas emissions. It is therefore necessary to be able to regulate said gas emissions.
[0005] During the operation of a vehicle equipped with an internal combustion engine, it is possible to distinguish two phases of different emissivities, directly correlated to the way in which the fuel is injected into the engine cylinders: - The warm-up phase, also called "warm up" in English terms, consists of priming an engine depollution catalyst, in particular a three-way catalyst, i.e. bringing it to a sufficient temperature so that it has a treatment efficiency at least equal to a predetermined threshold, for example 150°C. This phase is implemented cold, in particular after starting the engine when the catalyst temperature has had time to fall below its priming temperature. - The nominal phase called "hot catalyst" during which the catalyst is initiated. Controlling the quantity of oxygen in the latter makes it possible to ensure the reactions, in particular, in the case of a three-way catalyst, the oxidation reactions of unburned hydrocarbons HC and carbon monoxide CO, and the reduction reactions of nitrogen oxides, called NOx, in order to minimize the emissions of polluting species in the exhaust.
[0006] As an example, Figures 1 and 2 show cycles 1 and 2 of fuel injection into a cylinder of a spark-ignition internal combustion engine. In particular, the engine is a four-stroke engine and the injection, which is carried out in three stages, is called triple injection.
[0007] The cylinder forms a combustion chamber in which a piston driven by a crankshaft moves between a top dead center H, in other words a position of the piston for which the space remaining in the combustion chamber is minimal, and a bottom dead center B, in other words a position of the piston for which the space remaining in the combustion chamber is maximal.
[0008] In a four-stroke engine, there is an intake phase A between a top dead center H and a bottom dead center B, then a compression phase C between the bottom dead center B and a new top dead center H, and finally an expansion phase D between the new top dead center H and a new bottom dead center B. The expansion phase D is followed by an exhaust phase not shown.
[0009] In addition, since the crankshaft makes a 360° revolution, it is conventionally considered that the equivalent duration between two top dead centers, or two bottom dead centers, is equal to 360° of crankshaft angle, also noted 360°Crk (Crk for "Crankshaft", a term which designates the crankshaft in English). Also by convention, the origin of the crankshaft angle degree scale is fixed at top dead center H between the compression C and expansion D phases.
[0010] [Fig.l] illustrates a fuel injection cycle 1 for a nominal phase according to the state of the art.
[0011] Two injections 3 and 5 of fuel into the cylinder are carried out during the intake phase A, and a third 7 during the compression phase C. The ignition advance 9, also called ignition 9 and consisting of the production of a spark igniting the contents of the combustion chamber, is carried out shortly before the top dead center H at the end of the compression phase C.
[0012] [Fig.2] illustrates a fuel injection cycle 2 for a warm-up phase according to the state of the art.
[0013] Two injections 3 and 5 of fuel into the cylinder are carried out during the intake phase A, and a third 7 during the compression phase C. The ignition advance 11 is however degraded compared to [Fig.l] and this time takes place shortly after the top dead center H at the end of the compression phase C. This has the effect of degrading the combustion efficiency, and increasing the heat evacuated to the engine exhaust, and therefore into the catalyst, the efficiency of which increases with its temperature.
[0014] To minimize the exhaust emissions of an engine during the warm-up phase, according to a first method, the catalyst can be heated as quickly as possible. quickly as possible in order to start it quickly, and we can also, according to a second method, try to minimize emissions at source, that is to say the emission of polluting molecules present in the combustion gases at the exit of the engine cylinder head, before the pollution control device(s) including the catalyst.
[0015] However, heating the catalyst too quickly may involve setting up a very polluting combustion cycle in the engine, which leads to the deterioration of emissions at the source, contrary to the objective of the second method cited above. It is particularly well known to carry out a degradation of the ignition advance which makes it possible to increase the heat of the exhaust gases by degrading the combustion efficiency, but which also involves an increase in nitrogen oxide emissions at the engine outlet.
[0016] Moreover, minimizing the emissions present in the combustion gases at the outlet of the engine cylinder head is not easy to achieve. Disclosure of the invention
[0017] The present invention thus aims to overcome the above-mentioned drawbacks and to provide a means of minimizing the emissions of polluting gases, maximizing the temperature of the gases while having a combustion stability similar to that of a conventional triple injection.
[0018] The present invention relates to a method for heating a pollution control catalyst of a direct injection spark ignition engine comprising a piston cylinder driven between a top dead center position and a bottom dead center position by a rotating crankshaft, the method comprising during each fuel injection cycle:
[0019] - an injection step, called stratified, of fuel into the cylinder, starting between 0° and 90° crank angle after the piston has passed its top dead center, and in an expansion phase in the cylinder; and
[0020] - an ignition step, starting between 2 and 15° of crankshaft angle after the end of the stratified injection step.
[0021] Thus, the bringing together of these two stages of stratified injection and ignition in time, as well as their implementation during an expansion phase, makes it possible to minimize the emissions of polluting gases, to maximize the temperature of the gases while having combustion stability similar to a conventional triple injection. The injection is also called "stratified" due to the proximity of the ignition stage during implementation.
[0022] Preferably, the stratified injection step begins between 0° and 15° crank angle after the top dead center of the piston, preferably between 0° and 5° crank angle.
[0023] In a particular embodiment, the ignition step begins between 3° and 8° crankshaft angle after the end of the stratified injection stage.
[0024] Advantageously, the stratified injection step lasts between 5° and 15° of crankshaft angle.
[0025] Preferably, the method further comprises first, second and third successive steps of injecting fuel into the cylinder, the third injection step being the stratified injection step starting after the piston has passed its top dead center.
[0026] Advantageously, the second injection step begins between 55° and 20° crank angle before the piston exceeds its top dead center, preferably between 45° and 35° crank angle, in a compression phase in the cylinder.
[0027] Advantageously, the first injection step begins between 180° and 75° crank angle before the piston passes its top dead center, preferably between 90° and 75° crank angle, in a compression phase in the cylinder.
[0028] Preferably, between 20% and 33% of a total volume of fuel injected during the three fuel injection stages is injected during the third stratified injection stage, the remainder being injected in equal proportions during the first and second fuel injection stages.
[0029] In one embodiment, the method is implemented for an engine comprising a pollution control catalyst, and when said pollution control catalyst is at a temperature below a predefined temperature threshold.
[0030] This may in particular be a three-way catalyst, or any other type of pollution control catalyst present in the engine exhaust which needs to be primed to achieve minimum treatment efficiency, for example a nitrogen oxide trap.
[0031] The invention also relates to the method carried out for each cylinder of an engine comprising several cylinders, preferably at least three cylinders. Brief description of the drawings
[0032] Other aims, characteristics and advantages of the invention will appear on reading the following description, given solely by way of non-limiting example, and made with reference to the appended drawings in which:
[0033] [Fig.l] is a schematic view of a fuel injection cycle for a nominal driving phase according to the state of the art;
[0034] [Fig.2] is a schematic view of a fuel injection cycle for a warm-up phase according to the state of the art;
[0035] [Fig.3] is a schematic view of a first mode of implementation of the steps of a heating method according to the invention for a fuel injection cycle;
[0036] [Fig.4] is a schematic view of a second mode of implementation of the steps of a heating method according to the invention for a fuel injection cycle; and
[0037] [Fig.5] is a schematic view of a third preferred mode of implementing the steps of a heating method according to the invention for a fuel injection cycle.
[0038] Detailed description of at least one embodiment
[0039] Figures 3, 4 and 5 schematically show different modes of implementing the steps of a method for heating a depollution catalyst of a direct injection spark ignition engine according to the invention.
[0040] In particular, Figures 3, 4 and 5 show a single cycle 13, 14 or 15 of fuel injection into a cylinder of the engine for a warm-up phase. The method according to the invention consists of repeating this cycle 13, 14 or 15 for all the cylinders of the engine and throughout the warm-up phase of said catalyst.
[0041] The engine is for example a four-stroke engine.
[0042] The engine comprises at least one cylinder. Each cylinder forms a combustion chamber in which a piston driven by a rotating crankshaft moves between a top dead center H, in other words a position of the piston for which the space remaining in the combustion chamber is minimal, and a bottom dead center B, in other words a position of the piston for which the space remaining in the combustion chamber is maximal.
[0043] Preferably, the engine comprises several cylinders, for example three cylinders.
[0044] On cycles 13, 14 and 15 shown in figures 3, 4 and 5 we can distinguish a phase intake phase A between a top dead center H and a bottom dead center B, then a compression phase C between the bottom dead center B and a new top dead center H, and finally an expansion phase D between the new top dead center H and a new bottom dead center B. The expansion phase D is followed by an exhaust phase not shown.
[0045] Furthermore, since the crankshaft makes a 360° revolution, it is conventionally considered that the equivalent duration between two top dead centers H, or two bottom dead centers B, is equal to 360° of crankshaft angle. Also by convention, the origin of the crankshaft angle degree scale is fixed at top dead center H between the compression C and expansion D phases.
[0046] In each of the embodiments shown in Figures 3, 4 and 5, the method heating comprises, during each fuel injection cycle 13, 14 or 15, a step 17 of injection, called stratified, of fuel into the cylinder, the step 17 of stratified injection starting between 0° and 90° of crankshaft angle after the piston has passed its top dead center at the end of the compression phase C. In particular, the step 17 of stratified injection is carried out during the expansion phase D in the cylinder.
[0047] The method further comprises an ignition step 19, starting between 2 and 15° of crankshaft angle after the end of the stratified injection step 17. This ignition step 19 consists of creating a spark triggering combustion in the combustion chamber formed by the cylinder.
[0048] In a particular embodiment, the stratified injection step 17 begins between 0° and 15° crank angle after the top dead center H of the piston, preferably between 0° and 5° crank angle. A start of the stratified injection step 17 before the top dead center H would make the combustion of the fuel unstable.
[0049] The stratified injection step 17 lasts for example between 5° and 15° of crankshaft angle.
[0050] In a preferred embodiment, the ignition step 19 begins between 3° and 8° of crankshaft angle after the end of the stratified injection step.
[0051] In a particular embodiment, the stratified injection step 17 begins at the time of the top dead center H at the end of the compression phase C, lasts approximately 10° of crankshaft angle and the ignition step 19 begins approximately 15° after the top dead center H at the end of the compression phase C.
[0052] These two steps 17 and 19 carried out closely together, at less than 15° crankshaft angle, and both carried out during the expansion phase D, make it possible to minimize the emissions of polluting gases, to maximize the temperature of the gases while having combustion stability similar to a conventional triple injection as described in [Fig.2].
[0053] Combustion stability is measured using the standard deviation of the pressures of all combustion chambers of the engine over 500 injection cycles.
[0054] In the particular embodiments illustrated in Figures 3, 4 and 5, the method comprises a first, a second and a third successive steps 21, 23 and 17 of injecting fuel into the cylinder, the third injection step 17 being the stratified injection step 17 starting after the piston has passed its top dead center H at the end of the compression phase C.
[0055] In a particular embodiment, between 20% and 33% of a total volume of fuel injected during the three fuel injection steps 21, 23 and 17 is injected during the third stratified injection step 17, the remainder, namely between 67% and 80% of the total volume of fuel injected during the three fuel injection steps 21, 23 and 17 being injected in equal proportions during the first and second fuel injection steps 21 and 23. For example, 40% of the volume total fuel volume is injected during the first injection stage 21, 40% also during the second injection stage 23, and 20% of the total fuel volume is injected during the third stratified injection stage 17.
[0056] In the implementation mode illustrated in [Fig.3], the first and second injection steps 21 and 23 are carried out during the intake phase A, namely more than 180° of crankshaft angle before the top dead center H at the end of the compression phase C.
[0057] For an engine comprising three cylinders with a volume of between 300 and 400 cubic centimeters per cylinder, and in the embodiment illustrated in [Fig. 3], the quantity of hydrocarbon emitted at the outlet of the combustion chambers is 960 ppm, in other words parts per million. For comparison, a conventional triple injection such as that illustrated in [Fig. 1] emits 1560 ppm of hydrocarbon. An improvement is therefore observed.
[0058] Similarly, the quantity of carbon monoxide emitted for the implementation mode illustrated in [Fig.3] is 7790 ppm compared to 5000 ppm for the conventional implementation mode of [Fig.l]. For this gas, a deterioration in performance is therefore observed.
[0059] The quantity of nitrogen oxides emitted for the implementation method illustrated in [Fig.3] is 785 ppm compared to 1530 ppm for the conventional implementation method of [Fig.l]. An improvement is therefore noted.
[0060] The temperature measured at the exhaust for the implementation mode illustrated in [Fig.3] is 739°C compared to 685°C for the conventional implementation mode of [Fig.l]. An improvement is therefore noted.
[0061] Furthermore, the combustion stability is not greatly impacted and remains substantially constant between the implementation mode of [Fig.l] and that of [Fig.3].
[0062] In the implementation mode illustrated in [Fig.4], the first injection step 21 is carried out during the intake phase A, namely more than 180° of crankshaft angle before the top dead center H at the end of the compression phase C.
[0063] The second injection step 23 begins between 55° and 20° crank angle before the piston passes its top dead center H, preferably between 45° and 35° crank angle, during the compression phase C in the cylinder. Even more preferably, the second injection step 23 begins around 40° crank angle before the piston passes its top dead center H.
[0064] For an engine comprising three cylinders with a volume of between 300 and 400 cubic centimeters per cylinder, and in the embodiment illustrated in [Fig.4], the quantity of hydrocarbon emitted at the outlet of the combustion chambers is 640 ppm. For comparison, a conventional triple injection such as that illustrated in [Fig.l] emits 1560 ppm of hydrocarbon. An improvement is therefore noted.
[0065] Similarly, the quantity of carbon monoxide emitted for the implementation mode illustrated in [Fig.4] is 8400 ppm compared to 5000 ppm for the conventional implementation mode of [Fig.l]. For this gas, a deterioration in performance is therefore observed.
[0066] The quantity of nitrogen oxides emitted for the implementation method illustrated in [Fig.4] is 470 ppm compared to 1530 ppm for the conventional implementation method of [Fig.l]. An improvement is therefore observed.
[0067] The temperature measured at the exhaust for the implementation mode illustrated in [Fig.4] is 745°C compared to 685°C for the conventional implementation mode of [Fig.l]. An improvement is therefore noted.
[0068] Furthermore, the combustion stability is not greatly impacted and remains substantially constant between the implementation mode of [Fig.l] and that of [Fig.4].
[0069] In the embodiment illustrated in [Fig.5], the first injection step 21 begins between 180° and 75° crank angle before the piston passes its top dead center H at the end of the compression phase C, preferably between 90° and 75° crank angle. Even more preferably, the first injection step 21 begins around 80° crank angle before the piston passes its top dead center H.
[0070] The second injection step 23 begins between 55° and 20° crank angle before the piston passes its top dead center H, preferably between 45° and 35° crank angle, during the compression phase C in the cylinder. Even more preferably, the second injection step 23 begins around 40° crank angle before the piston passes its top dead center H.
[0071] For an engine comprising three cylinders with a volume of between 300 and 400 cubic centimeters per cylinder, and in the embodiment illustrated in [Fig.5], the quantity of hydrocarbon emitted at the outlet of the combustion chambers is 410 ppm. For comparison, a conventional triple injection such as that illustrated in [Fig.l] emits 1560 ppm of hydrocarbon. A significant improvement is therefore observed.
[0072] Similarly, the quantity of carbon monoxide emitted for the implementation mode illustrated in [Fig.4] is 6340 ppm compared to 5000 ppm for the conventional implementation mode of [Fig.l]. For this gas, a deterioration in performance is observed but less than for the implementation modes of Figures 3 and 4. This embodiment illustrated in [Fig.5] is therefore particularly advantageous.
[0073] The quantity of nitrogen oxides emitted for the implementation method illustrated in [Fig.5] is 480 ppm compared to 1530 ppm for the conventional implementation method of [Fig.l]. An improvement is therefore observed.
[0074] The temperature measured at the exhaust for the implementation mode illustrated in [Fig.5] is 785°C compared to 685°C for the conventional implementation mode of [Fig.l]. An improvement is therefore noted.
[0075] Furthermore, the combustion stability is not greatly impacted and remains substantially constant between the implementation mode of [Fig.l] and that of [Fig.5].
[0076] The method which is the subject of the invention is preferably implemented for an engine comprising a pollution control catalyst and only when said catalyst is at a temperature below a predefined temperature threshold, for example 150°C.
Claims
Claims
1. Method for heating a depollution catalyst of a direct injection spark ignition engine comprising a piston cylinder driven between a top dead center position (H) and a bottom dead center position (B) by a rotating crankshaft, characterized in that it comprises during each fuel injection cycle: - a step (17) of injection, called stratified, of fuel into the cylinder, starting between 0° and 90° of crankshaft angle after the piston has passed its top dead center (H), and in an expansion phase (D) in the cylinder; and - an ignition step (19), starting between 2 and 15° of crankshaft angle after the end of the stratified injection step (17).
2. Method according to claim 1, wherein the step (17) of stratified injection starts between 0° and 15° of crank angle after the top dead center (H) of the piston, preferably between 0° and 5° of crank angle.
3. Method according to one of claims 1 and 2, in which the ignition step (19) begins between 3° and 8° of crankshaft angle after the end of the stratified injection step (17).
4. A method according to any one of claims 1 to 3, wherein the stratified injection step (17) lasts between 5° and 15° of crank angle.
5. A method according to any one of claims 1 to 4, comprising successive first, second and third steps (21, 23, 17) of injecting fuel into the cylinder, the third injection step (17) being the stratified injection step (17) commencing after the piston has passed its top dead center (H).
6. Method according to claim 5, in which the second injection step (23) starts between 55° and 20° of crank angle before the piston passes its top dead center (H), preferably between 45° and 35° of crank angle, in a compression phase (C) in the cylinder.
7. Method according to one of claims 5 and 6, in which the first injection step (21) begins between 180° and 75° crank angle before the piston exceeds its top dead center (H), preferably between 90° and 75° crank angle, in a compression phase (C) in the cylinder.
8. A method according to any one of claims 5 to 7, wherein between 20% and 33% of a total volume of fuel injected during the three fuel injection stages (21, 23, 17) is injected during the third stratified injection stage (17), the remainder being injected in equal proportions during the first and second fuel injection stages (21, 23).
9. Method according to any one of claims 1 to 8, implemented for an engine comprising a pollution control catalyst and when said pollution control catalyst is at a temperature below a predefined temperature threshold.
10. Method according to any one of claims 1 to 9, carried out for each cylinder of an engine comprising several cylinders, preferably at least three cylinders.