Method for heating an engine's pollution control catalyst
The stratified fuel injection and timed ignition method addresses the challenge of catalyst heating in spark-ignition engines by minimizing emissions and enhancing catalyst efficiency during the warm-up phase.
Patent Information
- Application Number
- FR2023012664
- Authority / Receiving Office
- FR · FR
- Patent Type
- Utility models
- Current Assignee / Owner
- Filing Date
- 2023-11-17
- Publication Date
- 2025-11-07
- Estimated Expiration
- 2033-11-17
AI Technical Summary
Existing methods for heating pollution control catalysts in spark-ignition engines face challenges in minimizing emissions during the warm-up phase while maintaining combustion stability, often leading to increased nitrogen oxide emissions and inefficient heat transfer.
A method involving stratified fuel injection and timed ignition during the expansion phase, with specific timing and fuel distribution across multiple injection stages, to enhance catalyst heating and minimize pollutant emissions.
The method effectively reduces hydrocarbon, carbon monoxide, and nitrogen oxide emissions while maintaining combustion stability, achieving higher exhaust temperatures and improved catalyst efficiency.
Smart Images
Figure 00000012_0000 
Figure 00000012_0001 
Figure 00000012_0002
Abstract
Description
Title of the invention: Method for heating a pollution control catalyst in an engine 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 of injecting fuel into the cylinders of an engine for heating up a pollution control catalyst of said engine, the heating enabling the improvement of the treatment performance of polluting molecules emitted in the combustion gases of said engine by said pollution control catalyst.
[0003] In general, 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 reducing pollution from internal combustion engines, particularly spark-ignition engines, which run, for example, on gasoline as fuel, and whose emissions standards impose increasingly lower limits on pollutant emissions. It is therefore necessary to be able to regulate these 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 known as "warm-up" in English, consists of priming an engine's emissions control catalyst, particularly a three-way catalyst, by bringing it to a temperature sufficient for its treatment efficiency to be at least equal to a predetermined threshold, for example 150°C. This phase is carried out when the engine is cold, particularly after starting the engine, once the catalyst temperature has had time to drop below its priming temperature. - The nominal phase known as "hot catalyst" during which the catalyst is initiated. Controlling the amount of oxygen in the latter ensures 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 emission of polluting species in the exhaust.
[0006] By way of 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 takes place 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 remaining space in the combustion chamber is minimal, and a bottom dead center B, in other words a position of the piston for which the remaining space 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 a power phase D between the new top dead center H and a new bottom dead center B. The power phase D is followed by an exhaust phase not shown.
[0009] Furthermore, since the crankshaft completes a 360° revolution, it is conventionally considered that the equivalent time between two top dead centers, or two bottom dead centers, is equal to 360° of crankshaft angle, also denoted 360°Crk (Crk for "Crankshaft"). Also by convention, the origin of the crankshaft angle scale is fixed at top dead center H between the compression stroke C and the expansion stroke D.
[0010] Fig. 1 illustrates a fuel injection cycle 1 for a nominal phase according to the prior 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, takes place shortly before the top dead center H at the end of the compression phase C.
[0012] Figure [Fig. 2] illustrates a cycle 2 of fuel injection for a warm-up phase according to the prior art.
[0013] Two fuel injections 3 and 5 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.1] and is carried out this time 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 removed from the engine exhaust, and therefore into the catalyst, whose efficiency increases with its temperature.
[0014] To minimize exhaust emissions from an engine during the warm-up phase, a first method can be used to heat the most efficient catalyst. as quickly as possible in order to start it up quickly, and we can also, according to a second method, try to minimize emissions at the source, that is to say the emission of polluting molecules present in the combustion gases at the exit of the cylinder head of the engine, before the pollution control device(s) including the catalyst.
[0015] However, excessively rapid heating of the catalyst can lead to a highly polluting combustion cycle in the engine, resulting in a deterioration of emissions at the source, contrary to the objective of the second method mentioned above. It is particularly well known that degrading the ignition timing increases the heat of the exhaust gases by reducing combustion efficiency, but this also leads to an increase in nitrogen oxide emissions from the engine.
[0016] Furthermore, minimizing emissions present in the combustion gases at the outlet of the engine cylinder head is not easy to achieve. Description of the invention
[0017] The present invention therefore aims to overcome the aforementioned disadvantages and to provide a means of minimizing emissions of polluting gases, maximizing the temperature of the gases while having combustion stability similar to a conventional triple injection.
[0018] The present invention relates to a method for heating a pollution control catalyst in 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] - a stratified injection stage of fuel into the cylinder, beginning between 0° and 90° crankshaft angle after the piston has passed its top dead center, and during a power stroke in the cylinder; and
[0020] - an ignition stage, beginning between 2 and 15° crankshaft angle after the end of the stratified injection stage.
[0021] Thus, combining these two stages of stratified injection and ignition in time, and implementing them during a pressure expansion phase, minimizes pollutant emissions, maximizes gas temperature, and provides combustion stability similar to conventional triple injection. The injection is also described as "stratified" due to the proximity of the ignition stage during its implementation.
[0022] Preferably, the stratified injection step begins between 0° and 15° crankshaft angle after the top dead center of the piston, preferably between 0° and 5° crankshaft 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° crankshaft angle.
[0025] Preferably, the method further comprises a first, a second and a third successive stages of fuel injection into the cylinder, the third injection stage being the stratified injection stage beginning after the piston has passed its top dead center.
[0026] Advantageously, the second injection stage begins between 55° and 20° crankshaft angle before the piston passes its top dead center, preferably between 45° and 35° crankshaft angle, in a compression phase in the cylinder.
[0027] Advantageously, the first injection stage begins between 180° and 75° crankshaft angle before the piston passes its top dead center, preferably between 90° and 75° crankshaft 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 include a three-way catalyst, or any other type of pollution control catalyst present in the engine exhaust which needs to be primed to achieve a 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 objects, features and advantages of the invention will become apparent from the following description, given solely by way of non-limiting example, and made with reference to the accompanying drawings in which:
[0033] [Fig.1] 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 prior art;
[0035] [Fig.3] is a schematic view of a first method of implementing the steps of a heating process according to the invention for a fuel injection cycle;
[0036] [Fig.4] is a schematic view of a second implementation method for the steps of a heating process 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 process according to the invention for a fuel injection cycle.
[0038] Detailed description of at least one embodiment
[0039] Figures 3, 4 and 5 schematically represent different modes of implementation of the steps of a process for heating a pollution control catalyst of a direct injection spark-ignition engine according to the invention.
[0040] In particular, Figures 3, 4, and 5 show a single fuel injection cycle 13, 14, or 15 in one engine cylinder during a warm-up phase. The method according to the invention consists of repeating this cycle 13, 14, or 15 for all engine cylinders 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 remaining space in the combustion chamber is minimal, and a bottom dead center B, in other words a position of the piston for which the remaining space in the combustion chamber is maximal.
[0043] Preferably, the engine comprises several cylinders, for example three cylinders.
[0044] A phase can be distinguished on cycles 13, 14 and 15 shown in figures 3, 4 and 5 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 a power phase D between the new top dead center H and a new bottom dead center B. The power phase D is followed by an exhaust phase not shown.
[0045] Furthermore, since the crankshaft completes a 360° revolution, it is conventionally considered that the equivalent time 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 scale is fixed at top dead center H between the compression stroke C and the expansion stroke D.
[0046] In each of the embodiments shown in Figures 3, 4 and 5, the process The warm-up procedure includes, during each fuel injection cycle 13, 14 or 15, a stratified injection stage 17 of fuel in the cylinder, the stratified injection stage 17 beginning between 0° and 90° crankshaft angle after the piston has passed its top dead center at the end of the compression phase C. In particular, the stratified injection stage 17 is carried out during the expansion phase D in the cylinder.
[0047] The method further includes an ignition step 19, beginning between 2 and 15° crankshaft angle after the end of the stratified injection step 17. This ignition step 19 consists of creating a spark that triggers combustion in the combustion chamber formed by the cylinder.
[0048] In a particular embodiment, the stratified injection step 17 begins between 0° and 15° of crankshaft angle after top dead center H of the piston, preferably between 0° and 5° of crankshaft angle. Beginning the stratified injection step 17 before top dead center H would make fuel combustion 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 of 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 of the end of the compression phase C.
[0052] These two steps 17 and 19, carried out in close proximity, at less than 15° crankshaft angle, and both performed during the expansion phase D, make it possible to minimize pollutant gas emissions, maximize gas temperature 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 the engine's combustion chambers 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 stages 21, 23 and 17 of fuel injection into the cylinder, the third stage 17 of injection being the stratified injection stage 17 beginning after the piston has passed its top dead center H of the end of the compression phase C.
[0055] In a particular embodiment, between 20% and 33% of the total volume of fuel injected during the three fuel injection stages 21, 23, and 17 is injected during the third stratified injection stage 17, the remainder, namely between 67% and 80% of the total volume of fuel injected during the three fuel injection stages 21, 23, and 17, being injected in equal proportions during the first and second fuel injection stages 21 and 23. For example, 40% of the volume Total fuel is injected during the first stage 21 of injection, 40% also during the second stage 23 of injection, and 20% of the total fuel volume is injected during the third stage 17 of stratified injection.
[0056] In the embodiment illustrated in [Fig.3], the first and second injection steps 21 and 23 are carried out during the intake phase A, i.e. more than 180° crankshaft angle before the top dead center H of the end of the compression phase C.
[0057] For a three-cylinder engine with a volume between 300 and 400 cubic centimeters per cylinder, and in the embodiment illustrated in [Fig. 3], the quantity of hydrocarbon emitted from the combustion chambers is 960 ppm, or parts per million. By comparison, a conventional triple injection system 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 method illustrated in [Fig. 3] is 7790 ppm compared to 5000 ppm for the conventional implementation method in [Fig. 1]. 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.1]. An improvement is therefore observed.
[0060] The temperature measured at the exhaust for the embodiment illustrated in [Fig.3] is 739°C compared to 685°C for the conventional embodiment of [Fig.1]. An improvement is therefore observed.
[0061] Moreover, the combustion stability is not greatly impacted and remains substantially constant between the implementation mode of [Fig.1] and that of [Fig.3].
[0062] In the embodiment illustrated in [Fig.4], the first injection step 21 is carried out during the intake phase A, namely more than 180° crankshaft angle before the top dead center H of the end of the compression phase C.
[0063] The second injection stage 23 begins between 55° and 20° crankshaft angle before the piston passes its top dead center H, preferably between 45° and 35° crankshaft angle, during the compression phase C in the cylinder. Even more preferably, the second injection stage 23 begins at around 40° crankshaft angle before the piston passes its top dead center H.
[0064] For an engine comprising three cylinders with a volume between 300 and 400 cubic centimeters per cylinder, and in the embodiment illustrated in [Fig. 4], the quantity of hydrocarbon emitted from the combustion chambers is 640 ppm. By comparison, a conventional triple injection system such as that illustrated in [Fig. 1] emits 1560 ppm of hydrocarbon. An improvement is therefore observed.
[0065] Similarly, the quantity of carbon monoxide emitted for the implementation method illustrated in [Fig. 4] is 8400 ppm compared to 5000 ppm for the conventional implementation method in [Fig. 1]. 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.1]. An improvement is therefore observed.
[0067] The temperature measured at the exhaust for the implementation illustrated in [Fig.4] is 745°C compared to 685°C for the conventional implementation in [Fig.1]. An improvement is therefore observed.
[0068] Moreover, the combustion stability is not greatly impacted and remains substantially constant between the implementation mode of [Fig.1] and that of [Fig.4].
[0069] In the embodiment illustrated in [Fig. 5], the first injection stage 21 begins between 180° and 75° crankshaft angle before the piston passes its top dead center H at the end of the compression phase C, preferably between 90° and 75° crankshaft angle. Even more preferably, the first injection stage 21 begins at approximately 80° crankshaft angle before the piston passes its top dead center H.
[0070] The second injection stage 23 begins between 55° and 20° crankshaft angle before the piston passes its top dead center H, preferably between 45° and 35° crankshaft angle, during the compression phase C in the cylinder. Even more preferably, the second injection stage 23 begins at around 40° crankshaft angle before the piston passes its top dead center H.
[0071] For a three-cylinder engine with a volume between 300 and 400 cubic centimeters per cylinder, and in the embodiment illustrated in [Fig. 5], the quantity of hydrocarbon emitted from the combustion chambers is 410 ppm. By comparison, a conventional triple injection system such as that illustrated in [Fig. 1] emits 1560 ppm of hydrocarbon. A significant improvement is therefore observed.
[0072] Similarly, the quantity of carbon monoxide emitted for the embodiment illustrated in [Fig. 4] is 6340 ppm compared to 5000 ppm for the conventional embodiment in [Fig. 1]. For this gas, a deterioration in performance is observed, but less so than for the embodiments in 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. 1]. An improvement is therefore observed.
[0074] The temperature measured at the exhaust for the embodiment illustrated in [Fig. 5] is 785°C compared to 685°C for the conventional embodiment of [Fig. 1]. An improvement is therefore observed.
[0075] Moreover, the combustion stability is not greatly impacted and remains substantially constant between the implementation mode of [Fig.1] and that of [Fig.5].
[0076] The method 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
Demands
1. A method for heating a pollution control catalyst for a direct-injection spark-ignition engine comprising a piston cylinder driven between a top dead center (H) position and a bottom dead center (B) position by a rotating crankshaft, characterized in that it comprises during each fuel injection cycle: - a stratified injection stage (17) of fuel into the cylinder, beginning between 0° and 90° crankshaft angle after the piston has passed its top dead center (H), and in an expansion phase (D) in the cylinder; and - an ignition stage (19), beginning between 2 and 15° crankshaft angle after the end of the stratified injection stage (17).
2. A method according to claim 1, wherein the stratified injection step (17) begins between 0° and 15° crankshaft angle after the top dead center (H) of the piston, preferably between 0° and 5° crankshaft angle.
3. A method according to any one of claims 1 and 2, wherein the ignition step (19) begins between 3° and 8° 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° crankshaft angle.
5. A method according to any one of claims 1 to 4, comprising a first, a second and a third successive stages (21, 23, 17) of fuel injection into the cylinder, the third stage (17) of injection being the stratified injection stage (17) beginning after the piston has passed its top dead center (H).
6. A method according to claim 5, wherein the second injection stage (23) begins between 55° and 20° crankshaft angle before the piston passes its top dead center (H), preferably between 45° and 35° crankshaft angle, in a compression phase (C) in the cylinder.
7. A method according to any one of claims 5 and 6, wherein the first injection stage (21) begins between 180° and 75° crankshaft angle before the piston passes its top dead center (H), preferably between 90° and 75° crankshaft 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 stages (21, 23, 17) of fuel injection is injected during the third stage (17) of stratified injection, the remainder being injected in equal proportions during the first and second stages (21, 23) of fuel injection.
9. A 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. A 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.