EP2193268A2 - Method for injecting fuel into an internal combustion engine cylinder - Google Patents

Abstract

The invention relates to a method for injecting fuel into an internal combustion engine cylinder, comprising one pre-injection (16), one or more main injections (4) at the combustion top dead centre, one after-injection (6) and one or more post-injections (18). The pre-injection (16) is performed just after the intake and exhaust valve overlap top dead centre. The fuel post-injection(s) are performed just before the intake and exhaust valve overlap top dead centre.

Description

 METHOD FOR INJECTING FUEL IN AN INTERNAL COMBUSTION ENGINE CYLINDER

DESCRIPTION

TECHNICAL AREA

The invention relates to a method for injecting fuel into an internal combustion engine cylinder in which one or more pre-injections, one or more main injections at the top dead center of combustion, an injection after and one or more are carried out. post-injections. The classic injection scheme of an engine

Diesel in the so-called normal injection phase whose exhaust line is equipped with a catalyst, a particulate filter and a NOx trap can be broken down into three phases: In a first phase, a pilot injection is carried out or pre injection. This phase comprises one to two injections phased between 40 ⁰ V and 20 ° V (V for crankshaft) before the top dead center of combustion. These pilot injections primarily reduce combustion noise but contribute in part to the dilution of fuel in the engine oil.

In a second phase, a main injection is made, also called "hand injection". This phase comprises only a single phase injection at the top dead point combustion. The main injection serves essentially to ensure the load of the engine. She is the main source of NOx and particulate emissions. It generates little combustion noise and little dilution.

In a third phase an injection is performed after ("after-injection"). This phase comprises only one injection phased between 10 ° V and 30 ⁰ V after the top dead point combustion. This injection is useful to restart combustion during relaxation and reduce smoke emissions by post-oxidation of soot. It generates little combustion noise but can contribute slightly to the dilution of the fuel in the oil.

Finally, during the regeneration phases performing a fourth phase called "post ^¬ injection." This phase comprises from one to three phase injections after the injection after and therefore well beyond the high combustion dead point, typically between 60 ° V and 100 ⁰ V after top dead center. The amount of fuel injected practically does not participate in the combustion in the cylinder; it goes directly to the exhaust and, via oxidation in the catalyst, it facilitates the initiation of the regeneration phases in the particulate filter and in the NOx trap. On the other hand, the post-injections contribute strongly to the increase of the dilution of the fuel in the oil because they are phased late in the cycle and directly impact the cylinder.

In summary, the main sources of fuel dilution in the engine oil are post-injections and pre-injections. It has been proposed in the prior art (US 2003/0033 800) a method of regenerating a particle filter for a diesel engine having a common rail injection system. This system allows a main injection, a first pre-injection preceding the main injection; a second pre-injection preceding the main injection and following the first pre-injection; a first post-injection following the main injection; and a second post-injection following the first post-injection is performed at the escape stroke. In this device, the post-injections can be performed with a late phasing that can reach 360 ⁰ V compared to the top dead point combustion. However, this device does not prevent the dilution of the fuel in the oil during the pre-injections.

In other diesel engines, there is a fifth injector (for a four-cylinder engine) or a seventh injector (for a six-cylinder engine). This additional injector is placed in the exhaust and it injects fuel directly into the exhaust. This solution solves post-injection problems but does not solve the problem of dilution related to pre-injection.

The present invention specifically relates to a method of injecting fuel into an internal combustion engine cylinder which overcomes these disadvantages. These objects are achieved, according to the invention, by the fact that the pre-mjection is performed just after the top dead center crossover intake and exhaust valves.

When the piston is close to a top dead center, whether it is the top dead center combustion or top dead center, its position varies very little. This is a feature of the kinematics connecting rod crank. The piston is very close to the fire side of the cylinder head and therefore the nose of the injector. Thus, the injected fuel is found almost exclusively in the piston bowl and thus the liquid gas oil does not come into contact with the oil film on the barrel.

According to a secondary feature of the invention the fuel injection or post-injections are performed just before the top dead center of the intake and exhaust valves.

In a particular embodiment, the pre-injection (s) are made 10 ⁰ V after the top dead center of the intake and exhaust valves.

In another particular embodiment the one or more post-injections are performed 10 ⁰ V before the upper dead center of crossing of the intake and exhaust valves. In one embodiment, the pre-injection (s) and the post-injection (s) are carried out in the form of a single injection which groups together the pre-injection (s) and the post-injection (s) in a single injection which is performed just after the top dead center crossover intake and exhaust valves. In a particular embodiment variant is used a variable distribution system type of offset to adjust the amount of fuel that goes to the exhaust. According to a first sub-variant, the intake and exhaust distribution laws are shifted in the direction of admission so as to obtain an increase in the fuel quantity of the post-injection and a reduction in the amount of fuel. pre injection fuel.

In a second variant, the intake and exhaust distribution laws are shifted towards the exhaust so as to obtain a reduction in the fuel quantity of the post-injection and an increase in the fuel quantity of the fuel. pre injection.

It is also possible to shift only the law of admission or only the law of escape. Other features and advantages of the invention will become apparent upon reading the following description of exemplary embodiments given by way of illustration with reference to the appended figures. In these figures: - Figure IA is a diagram showing the normal injection mode of a diesel engine according to the prior art; Fig. 1B is an enlarged view of a portion of Fig. 1A; - Figure 2A is a diagram showing the injection for the regeneration mode of a diesel engine according to the prior art; Figure 2B is an enlarged view of a portion of Figure 2A;

FIG. 3A is a diagram showing the normal injection mode of a diesel engine according to the present invention; Figure 3B is an enlarged view of a portion of Figure 3A;

FIG. 4A is a diagram showing the injection for the regeneration mode of a diesel engine according to the present invention; Figure 4B is an enlarged view of a portion of Figure 4A; Figure 5A is a variant of the injection mode for the regeneration mode shown in Figure 4A; Figure 5B is an enlarged view of a portion of Figure 5A; Figure 6 is a first sub-variant of the injection device shown in Figures 5A and 5B;

- Figure 7 is a second sub-variant of the injection device shown in Figures 5A and 5B.

FIGS. 1A and 1B show an injection scheme according to the prior art of a diesel engine for the normal injection mode, that is to say an injection outside the regeneration phases. As can be seen in Figures IA and IB one or more pre-injections 2, a main injection 4 and an injection after 6 are performed in each cylinder of the internal combustion engine. The pre-injection or pre-injections are carried out at 30 ° to 40 ^° C. before the high combustion dead point. The main injection is centered on the top dead point combustion and the injection after is located about 30 ⁰ V after the top dead point combustion. Thus, the pre-injection (s) are located in an unfavorable zone for the dilution or the limit of this zone. The main injection is located in the center of a favorable area for dilution and the after injection is located just on the boundary between the favorable zone for dilution and an unfavorable zone for dilution (substantially 30 ⁰ V).

Also shown in FIG. 1A is the representation of the law of emergence of the exhaust valve 10 and the law of emergence of the intake valve 12. The lifting of the exhaust valve extends substantially from 135 ° to 405 ° while the law of the lifting of the intake valve extends substantially from 315 ° to 585 °. As a result, the two curves intersect and there is a range of rotation of the crankshaft during which the intake and exhaust valve are open simultaneously. This range extends substantially 90 ° rotation of the crankshaft. The simultaneous opening of the intake and exhaust valves takes place when the piston is at the top dead center. There are indeed two top dead spots per cycle namely respectively the top dead point combustion at 0 ⁰ V and the top dead center crossing at 360 ⁰ V.

FIGS. 2A and 2B show a prior art injection scheme of a diesel engine for the regeneration mode of the particulate filter. This diagram is identical to FIGS. 1A and 1B except for one or more additional injections of post-injections 14 (3 in the example represents). These injections take place respectively at 60 °, 80 ° and 100 °. They are therefore all placed in an unfavorable zone for the dilution of the fuel in the engine oil.

Since the piston has largely exceeded the top dead center, a large part of the cylinder is discovered and the injected fuel comes to wash this oil.

FIGS. 3A and 3B show an injection diagram of a diesel engine according to the present invention for the normal injection mode, that is to say outside the regeneration phases. This scheme resembles that of Figures IA and IB. However, it differs in that the two pre- injections 2 have been moved. They are now just after the top dead center at the intersection of the intake and exhaust valves that is just after 360 ° crankshaft angle. In the example there are two pre-injections, but there could be more, for example three or more. As can be seen in FIG. 3A, the two pre-injections 16 are located in a favorable zone for dilution. Indeed, around the top dead center crossover the position of the piston varies very little and it is very close to the fire side of the cylinder head and thus the nose of the injector. Thus, the injected fuel is found almost exclusively in the piston bowl, that is to say in the depression dug in the piston. Thus, the liquid gas oil can not come into contact with the oil film present on the drum.

FIGS. 4A and 4B show an injection diagram of a diesel engine according to the present invention for the "regeneration" mode.

This scheme is similar to Figures 3A and 3B except that one or more post-injections 18 are found just before the top dead center of the intake and exhaust valves.

As can be seen in FIG. 4, these postmissions, which are located at about 10 ⁰ V to 40 ⁰ V before the top dead center, are located in a favorable zone for the dilution of the fuel in the oil present on the fuel. barrels of engine cylinders. In this scheme, the pre-injections are located after the post-mections because the pre-mjections are relative to the next engine cycle while the post-mjections are valid for the present engine cycle.

FIGS. 5A and 5B show a variant of the injection scheme of a diesel engine according to the present invention shown in FIG. 4A and 4B. In this embodiment, the pre-injections 16 and the post-mections 18 were grouped together in a single larger injection. 20. Injection 20 is located just after the top dead center of the intake and exhaust valves, that is to say just after 360 ⁰ V. As can be seen in the figure 5, this single injection 20 is entirely located in a favorable zone for dilution, which extends substantially from 300 ⁰ V to 420 ° V.

According to an alternative embodiment, the strategy represented in FIGS. 5A and 5B is coupled with a variable distribution system of the shifter type. A variable timing system is a system that varies the position of the camshaft which controls the intake and exhaust valves and thus the valve openings and closures as well as the opening times. There are several variable distribution systems among which we find the shifters also called "WT" for variable valve timing. These systems consist of shifting the camshafts that is to say to change the openings and closings of the valves without changing the duration during which the valve is opened or closed.

In Figure 6 the two laws have been shifted to admission. In other words, the new curve of lift of the exhaust valve and the new curve of the intake lift, represented in solid lines, have been shifted to the right (according to FIG. 6) with respect to the preceding schematized position. in dotted lines. The angular positioning of the injection 20 is not modified. It is always right after the top dead center of crossing the intake and exhaust valves. However, since the exhaust valve lift law has been displaced by about 45 °, a larger portion of the injected fuel goes directly to the intake while a smaller portion of the injected fuel is injected. -injection.

FIG. 7 shows an alternative embodiment of the diagram of FIG. 6. In FIG. 7 the law of the lifting of the exhaust valve and the law of the lifting of the intake valve are shifted towards the the value of this offset is approximately 45 °. In this embodiment, as in the previous embodiment, the angular position of the grouped injection 20 is not changed. It is always right after the top dead center of the intake and exhaust valves, that is to say 360 ⁰ V. However, since the exhaust valve is closed at the moment when begins fuel injection, no fraction of this fuel is delivered to the exhaust. The entire fuel is a pre-injection.

Of course it is not necessary to simultaneously shift the law of the valve lift of the exhaust and the law of lifting of the intake valve. One can very well shift only the law of admission or only the law of escape on the same principle (not represented).

Claims

A method of injecting fuel into an internal combustion engine cylinder in which a pre-injection (16), one or more main injections (4) are made at the top dead center, an injection after (6) and one or more post-injections (18) characterized in that the pre-injection (16) is performed just after the top dead center of the intake and exhaust valves. 2. Fuel injection method according to claim 1, characterized in that the fuel injection or post-injections (18) are made just before the top dead center of the intake and exhaust valves. 3. A method of fuel injection according to claim 1 or 2, characterized in that the or pre-injections (16) are performed 10 ° V after the top dead center of crossing the intake and exhaust valves. 4. Method according to claim 1 or 2, characterized in that the or the post-injections (18) are carried out 10 ° V before the top dead center of crossing of the intake and exhaust valves. 5. Method according to claim 2, characterized in that the or pre-injections (16) and the or the post-injections (18) are made in the form of a single injection (20) which groups together the -injections and the one or more post-injections in a single injection performed just after the breakeven point high crossover intake and exhaust valves. 6. A method according to claim 5, characterized in that one uses a variable distribution system of shifter type to adjust the amount of fuel leaving the exhaust. 7. Process according to claim 6, characterized in that the intake and exhaust distribution laws are shifted towards the intake so as to obtain an increase in the fuel quantity of the post-injection and a reduction in the amount of fuel pre-injection. 8. A method according to claim 6, characterized in that one shifts the intake and exhaust distribution laws towards the exhaust so as to obtain a reduction of the fuel quantity of the post-injection and an increase in the amount of fuel from the pre-injection. 9. The method of claim 6, characterized in that one shifts only the law of admission. 10. The method of claim 6, characterized in that one shifts only the exhaust law.