WO2008065287A1

WO2008065287A1 - Internal combustion engine exhaust system equipped with pollution reduction systems

Info

Publication number: WO2008065287A1
Application number: PCT/FR2007/052268
Authority: WO
Inventors: Frédéric TRONEL
Original assignee: Peugeot Citroën Automobiles SA
Priority date: 2006-11-27
Filing date: 2007-10-29
Publication date: 2008-06-05
Also published as: EP2084376A1; FR2909123A1; US20100071350A1; FR2909123B1

Abstract

Exhaust system for an internal combustion engine (1) of a motor vehicle which is equipped with a first oxidation catalytic converter or precatalytic converter (4) positioned near the outlet of gas from the engine, and with a particulate filter (9) associated with a second oxidation catalytic converter (8) these being positioned downstream of the precatalytic converter. It comprises first means for generating an increase in the temperature of the gases leaving the engine (1), second means for generating an exothermal reaction in the precatalytic converter (4) and third means (5) for generating an exothermal reaction in the catalytic converter (8) so as to split the burden of generating the increase in exhaust gas temperature required for regenerating the particulate filter (9) between the engine, the precatalytic converter and the catalytic converter.

Description

Exhaust gas line for internal combustion engine equipped with pollution control systems.

The invention relates to a gas exhaust line for a motor vehicle engine equipped with pollution control systems.

The pollutants resulting from the combustion of a motor vehicle engine whether it is a diesel engine or gasoline, are mainly unburned hydrocarbons, nitrogen oxides (nitrogen monoxide NO and nitrogen dioxide NO ₂ ), carbon oxides (carbon monoxide CO) and in the case of diesel engines and gasoline direct injection engines, carbonaceous solid particles.

In order to comply with international environmental standards, the control of HC, CO, NOx and particulate emissions is imperative and gas aftertreatment technologies are essential.

The clearance of motor vehicles uses different after-treatment systems to remove the pollutants produced by the engine: the catalysts, and the particulate filter in the case of diesel engines.

The particulate filter can filter out solid particles present in the exhaust gas of diesel engines. Once trapped within the filter, the particles must be removed periodically by raising the temperature to 450-700 ° C within the filter to cause their combustion. This operation is commonly called "regeneration" of the particulate filter. Conventionally the energy required for regeneration is provided by an increase in the temperature of the exhaust gas.

However, it is difficult for the motor to provide such a temperature, particularly in the case of the highest temperatures of 550 to 700 ° C. Classically, the excess energy in the exhaust compared to the normal operation of the engine is provided by the use of post-injections, that is to say of late fuel injections, after the top dead center of the cycle, or by degradation of the combustion efficiency.

In the case of the use of a post-injection it may burn completely or partially in the engine, generating an increase in the temperature of the exhaust gas or, if it is sufficiently late, lead to an increase in the amounts of CO and HC exhaust that oxidize upon arriving at the oxidation catalyst to generate heat.

This method causes a strong thermal stress on the catalyst closest to the engine which is subjected to each regeneration at a high temperature rise. In addition, the turbocharger and the exhaust manifold are also subjected to high temperatures. Finally, the heating methods from the engine lead to the dilution of diesel oil in the lubricating oil thereof, which is detrimental to its life.

The use of diesel injection in the exhaust makes it possible to solve most of these problems. In this case the heating from the engine is greatly reduced and the heat is generated by combustion of the gas oil introduced to the exhaust on the catalyst upstream of the particulate filter. The oil dilution is then greatly reduced as are the thermal stresses on the exhaust manifold and the turbocharger.

This technology is of particular interest in the case where the oxidation catalyst is split into a part close to the engine outlet (called pre-catalyst) and a part further from this outlet, for example, under the vehicle body ( called catalyst). In this case, the injection of diesel fuel between the two catalysts makes it possible to thermally solicit only the second catalyst during regeneration, the pre-catalyst then being solely dedicated to the oxidation of HC and CO from the engine.

The major drawback of this technology is the very high thermal load on the catalyst generating the exotherm (up to 400 or 500 ° C exotherm) and the need for a very high HC treatment capacity for the latter. to avoid smoke and odors in the exhaust.

The object of the invention is therefore to propose, in the case of an exhaust line comprising a catalyst associated with a particulate filter, a strategy for generating, upstream of the particulate filter, a sufficiently high temperature to cause total combustion of the particles, without excessive stress on the engine or the catalyst.

For this purpose, the subject of the present invention is a gas exhaust line for an internal combustion engine of a motor vehicle equipped with a first oxidation catalyst or pre-catalyst placed close to the exit of the engine gases and a particle filter associated with a second oxidation catalyst placed downstream of the pre-catalyst. According to the invention, it comprises first means for generating an increase in the temperature of the gases leaving the engine, second means for causing an exothermic reaction in the pre-catalyst and third means for causing an exothermic reaction in the second catalyst. so as to distribute the generation of the temperature rise of the exhaust gas, necessitated by the regeneration of the particulate filter, between the engine, the pre-catalyst and the second catalyst.

According to other advantageous features of the invention:

- The means for generating an increase in the temperature of the gas output of the engine are able to cause a degradation of the combustion efficiency.

• The degradation of the combustion efficiency is obtained by under-setting the main fuel injection, that is to say by a later injection with respect to the top dead center of the cycle.

• The main injection is delayed by 2 to 20 ° of crank angle compared to a normal injection.

the degradation of the combustion efficiency is obtained by reducing the quantity of ai r admitted into the engine.

The means for generating an increase in the temperature of the gases leaving the engine makes it possible to obtain, upstream of the pre-catalyst, a gas temperature of between 200 and 650 ° C.

• The means for causing an exothermic reaction in the pre-catalyst are able to trigger a post-fuel injection phase in the engine.

• The post injection is late and between 90 to 240 ° angle of the crankshaft.

• The temperature of the exothermic reaction in the precatalyst is between 20 and 200 ° C.

The means for generating an exothermic reaction in the catalyst is a fuel introduction device disposed between the pre-catalyst and the catalyst.

The temperature of the exothermic reaction in the catalyst is between 20 and 300 ° C.

The three means for heating the exhaust gases are activated successively as a function of the difference between the temperature of the gases at the outlet of the engine and that necessary upstream of the particulate filter to ensure the regeneration of the latter.

At least two of the exhaust gas heating means are activated simultaneously. "Both exothermic reactions are produced simultaneously and controlled to ensure the best compromise between HC treatment and fuel consumption.

• With strong engine and medium and strong load, the means to generate a rise in the temperature of the gas output of the engine are made preponderant compared to the other two gas heating means.

• The control of the heating means is predefined by cartography.

- The control of the heating means is a closed-loop control.

• The regulation uses one or more temperatures measured, by sensor, at different points of the exhaust line.

- The regulation of the means generating the exothermic reactions takes into account the flow of gas to the exhaust.

When the means for generating an increase in the temperature of the gases at the output of the engine operate by under-setting the main injection, the regulation acts on the sub-setting angle thereof, with respect to an angle of 90.degree. ° of the crankshaft n.

• To regulate the exothermic reaction on the pre-catalyst the amount and the phase of the post-injection are adjusted.

To control the exothermic reaction on the catalyst, the average flow rate of the fuel i injected to the exhaust is plotted.

• To control the strategy of the gas temperature rise, the control modes are pre-determined by mapping and closed-loop control. For example, a cartographic control of the motor heating is coupled to a regulation by sensor for exothermic reactions in the precatalyst and in the catalyst.

During the regeneration phase, the means for heating the exhaust gases are used either continuously, intermittently or in continuously variable amounts.

The second catalyst is located upstream of the particulate filter or integrated on the same support.

The fuel comprises an additive that aids the regeneration of the particulate filter.

Other characteristics and advantages of the invention will become clear from reading the following description, given as an indication with reference to the appended drawings, in which:

FIG. 1 is a block diagram of an exhaust line according to the invention.

- Figure 2 is a graph of temperatures at different points of the exhaust line, depending on the speed of the engine.

FIG. 3 is a graph illustrating an example of a change of heating mode during a load reduction of the motor.

FIGS. 4, 5 and 6 illustrate examples of distributions of the heating modes on the motor field. FIGS. 7 and 8 are examples of control of the various heating means and

FIG. 9 shows examples of injection sequence.

The block diagram of FIG. 1 illustrates an example of an exhaust line according to the invention.

This line comprises, as is known, a motor 1, for example a four-cylinder diesel engine, at the output of which there is an exhaust manifold 2 and a turbocharger 3, opening into the exhaust line.

This exhaust line comprises a first catalyst or pre-catalyst 4 placed near the engine gas outlet which makes it possible to treat the HC and CO emissions of the engine

At the outlet of the pre-catalyst 4, a device 5 allows the introduction of fuel such as, for example, diesel into the exhaust line.

This device comprises, for example, introduction control means 6 from a fuel tank 7 of the vehicle or the fuel system of the vehicle.

The fuel introduction device 5 is disposed between the pre-catalyst 4 and a second catalyst 8 associated with a particulate filter 9.

The catalyst 8 and the particulate filter 9 are arranged at a sufficient distance from the means 5 for introducing fuel into the exhaust line to allow good homogenization of the gas / fuel mixture.

According to the invention, it is intended to generate a high temperature, between 400 and 800 ° C. (preferably between 450 and 700 ° C.), upstream of the particulate filter, without excessive stress on the engine or the catalyst in order to obtain the regeneration of said filtered.

To do this, the strategy consists of distributing the temperature rise between the engine, the pre-catalyst and the catalyst.

For this purpose, an increase in the temperature of the gases at the outlet of the engine 1 and an exothermic reaction are generated in the pre-catalyst 4 and in the catalyst 8.

The rise in the temperature of the gases at the outlet of the engine 1 can be obtained by degradation of the combustion efficiency, for example by undercooling of the injection main, that is to say by a later injection compared to top dead center (TDC), by a post-injection totally burning in the engine, by winnowing admission or any combination of these known means.

In FIG. 9b, there is shown an injection sequence with undercurrent of the main injection, it can be seen that with respect to a conventional injection, as represented in FIG. 9a, the main injection is displaced from 2 to 20 ° C. crankshaft angle.

It is thus intended to obtain, upstream of the pre-catalyst 4, a gas temperature of between 200 and 650 ° C. Under the most common operating conditions of the engine this temperature range will be between 250 and 400 ° C. This corresponds to a temperature rise of 50 to 350 ° C compared to the non-regeneration mode of operation.

The exothermic reaction on the pre-catalyst 4 will be obtained with the aid of a post injection, this being preferably late, in order to limit the dilution of the lubricating oil. In Figure 9b, there is shown such a post injection, between 90 to 240 ° crank angle, while a conventional post injection (Figure 9c) is between 20 to 90 crank angle. Preferably, this late post-injection will be between 1 20 to 1 80 ° crank angle.

The more a post injection is close to the main injection, the more it generates heat at the motor output. On the contrary, a later post injection generates CO emissions, due to incomplete combustion, and HC. The later the post injection, the lower the amount of heat produced and the more the exhaust gas contains HC.

These CO and HC emissions are oxidized by arriving at the pre-catalyst and generating heat. In order not to subject the latter to too high temperatures, the temperature of the exothermic reaction thus created will be between 20 and 200 ° C, in most cases between 50 and 150 ° C.

The exothermic reaction on the catalyst 8 is generated by the fuel introduction device 5 which sends into the catalyst hydrocarbons whose oxidation will cause a significant release of heat. It will be sought to obtain a temperature of the exothermic reaction thus created between 20 and 300 ° C., in most cases between 50 and 200 ° C.

The diagram of FIG. 2 represents the temperatures at the outlet of each of the elements contributing to the heating of the exhaust line, as a function of the speed of the engine: Θ1 is the temperature at the outlet of the turbocharger 3, during normal engine operation, c that is, outside the regeneration phase of the particulate filter; Θ2 is the temperature at the outlet of the turbocharger in the regeneration phase, Θ3 is the temperature at the outlet of the pre-catalyst 4 and Θ4 the temperature at the outlet of the catalyst 8. Θ2, Θ3, Θ4 are, of course, the temperatures reached according to the teachings of the present invention. Zone Z, in gray, is the temperature zone for the regeneration of the particulate filter.

It can be seen that the amplitude of the curves varies according to the operating ranges of the motor. In areas where the engine is operating at high load, for example the end of the cycle as shown in the figure, only one or two of the three means used are sufficient to ensure the required temperature rise. It is therefore possible to control, accordingly, the activation of the various heating means.

FIG. 3 illustrates the possible modes of activation of these various means when the engine load decreases during the regeneration period of the particulate filter. When the load decreases, the temperature at the motor output Θ5 also decreases. In the part ® of the graph, this temperature is, however, sufficient for the temperature Θ7, upstream of the particulate filter allows the regeneration thereof without the need for additional heating.

In part Φ of the graph, the motor output temperature becomes insufficient to ensure regeneration alone. Fuel is then injected into the exhaust to cause an exothermic reaction in the catalyst 8, the temperature Θ9 at the outlet thereof increases so that Θ7 remains in the regeneration zone.

In part Φ, after a further decrease in the motor output temperature Θ5, an exothermic reaction is also caused in the pre-catalyst 4 so as to increase the temperature Θ8 at the outlet thereof.

Finally, if the temperature Θ5 of the engine drops further, in the case of the part © of the graph, it triggers, in addition, the means provided to raise the engine temperature Θ6.

Thanks to the successive activation of the various means of heating the exhaust gas, it is found that the temperature Θ7 upstream of the particulate filter has remained substantially constant.

Instead of successive activation, it may be wise to provide simultaneous activation of two or three of the heating means by modulating their effects. The exothermic reaction in the catalyst 8 and in the pre-catalyst 4 can be activated simultaneously but in variable proportions to find the best compromise between the treatment of HC emissions for which warming of the pre-catalyst is preferable but which penalizes the consumption, which is less important in the case where the catalyst is heated by fuel injection to the exhaust.

Figures 4 to 6 show such distributions on the motor field. In zone A of the graphs of FIGS. 4, 5 and 6, normal engine warm-up is sufficient, no additional strategy is involved.

In the strategy example presented in FIG. 4, an exothermic reaction is successively carried out in the catalyst 8 (zone B) and in the pre-catalyst 4 (zone C), whereas in the example shown in FIG. 5 the two exothermic reactions are produced simultaneously in both zones B and C and piloted in order to ensure the best compromise HC / consumption treatment.

In zone D of the two graphs, the motor heating is also activated.

In addition to these transitions, at high engine speed and medium and high load, the high flow rates of the exhaust gases make the exothermic reaction more difficult to generate without causing too much HC emission, so we prefer the engine heating, compared to the other means (zone E of the graphs).

In the third exemplary strategy shown in FIG. 6, the generation of exotherms is only used in the zones of the engine field where engine heating is difficult and a source of dilution of the fuel in the lubricating oil (zone F). In the other zones (zone G), the heating is generated solely by the motor.

The control of the heating means can be done in different ways.

For example, in a predetermined manner, by mapping. At the same point of the engine speed / load curve is always the same value for each of the heating means. In this case, no specific sensor is needed.

Or by closed-loop regulation. This regulation can be done from one or more temperatures measured, by sensor, at different points of the line exhaust. The temperatures can be measured between the outlet of the turbocharger 3 and the pre-catalyst 4, between the pre-catalyst 4 and the catalyst 8, and downstream of the catalyst 8. In addition, an additional point can be raised downstream of the filter. particles 9.

In addition to the temperature, the regulation of the means generating the exothermic reactions can also take into account the exhaust gas flow rate. This flow can be measured or estimated.

With regard to the motor heating, if it is carried out by means of a post-injection, the regulation will act on the quantity and the phasing of it. If it is achieved by a delay of the main injection, the regulation will act on the sub-pitch angle and the amount thereof, with respect to a 90 ° angle of the crankshaft.

Similarly, we can adjust the amount and phasing of the post-injection ensuring the exothermic reaction on the precatalyst.

The piloting of the average flow rate of the fuel injected into the exhaust will still make it possible to vary the exothermic reaction of the catalyst. This control can be performed from the temperature upstream of the particulate filter.

Finally, it is also possible to combine these control modes.

For example, FIG. 7 shows a control mode in which a cartographic control of the motor heating is coupled to a sensor regulation for the exothermic reactions: the temperature T1 upstream of the catalyst is measured and compared with the temperature T2 which one it is desired to obtain upstream of the particulate filter, the amounts of heat that must be created in the pre-catalyst (Q1) and in the catalyst (Q2) are thus adjusted continuously. In FIG. 8, it is the temperature T3 upstream of the particulate filter that allows the regulation, the quantities of heat in the pre-catalyst (Q3) and in the catalyst (Q4) are, they, piloted in all or nothing .

Of course, these examples are not limiting and one could, without departing from the scope of the invention choose other modes of control of the heating means.

Similarly, the heating means can be used during the regeneration phase, in the various applicable control modes, continuously, intermittently or in continuously variable quantities of the PID type, according to the formula:

Heating requirement = Pre-positioning [motor point] + K _p x (T-value) + K ₁ xj (T-value) + K _d x I T-value / Tm (T-value) xd (T-value) / dt

The quantity injected is thus calculated by summing a quantity dependent on the driving point, by an amount proportional to the difference between the temperature reached and the target temperature, by an amount proportional to the derivative relative to the time of the the difference between the temperature reached and the target temperature (which will be deducted if the difference between the temperature reached and the target temperature is positive and added if the difference is negative) and a quantity proportional to the integral of the temperature. difference over a time much greater than the scale of variation of temperatures.

It will be further specified that the different heating means may use the same type of regulation or different modes.

As is well known, the different injections used to obtain the exothermic reactions can also be split into several injections.

As we have understood, reading the above, spreading the temperature rise of the line exhaust, required by the regeneration of the particle filter, between three elements of this line, the invention makes it possible to minimize the stresses on all the elements of this line.

The dilution of oil within the engine and the temperature at the outlet thereof will be lower.

The pre-catalyst, which mainly contributes to the depollution on regulatory cycle, will not undergo accelerated aging.

The exothermic reactions remaining limited on the two catalysts, their material does not need specific formulation, compared to those commonly used.

The amount of HC to be treated by the catalysts is low, in particular for the catalyst located upstream of the particulate filter, which receives the gases injected into the exhaust and under good conditions (hot upstream gases). The risk of HC emissions (fumes, odor) is therefore lower.

This strategy also allows a limitation of heat losses and thus a gain in consumption during the regeneration phases of the particulate filter. In fact, the heat generated in the form of an exothermic reaction at the level of the catalysts results in less heat loss than that created at the motor level.

Finally this strategy allows a better regeneration efficiency in all conditions and in particular in areas of low load. As the temperature target attached to the engine is lower (200-350 ° C) it can be obtained in all driving conditions even the most severe (typically low speed).

The invention is applicable to all internal combustion engines equipped with a particulate filter, diesel engine, lean-burn gasoline engine ... It can also be used when the catalyst is situated upstream of the particulate filter, as in the example described above, only when the catalyst is directly impregnated in the particulate filter. In addition, and in all cases, a regeneration aid additive may be added to the fuel.

Claims

1. Exhaust gas line for an internal combustion engine of a motor vehicle equipped with a first oxidation catalyst or pre-catalyst placed near the exit of the engine gases, and a particle filter associated with a second catalyst of oxidation placed downstream of the precatalyst, characterized in that it comprises first means, capable of causing a degradation of the combustion efficiency, to generate an increase in the temperature of the gases at the outlet of the engine (1), second means for causing an exothermic reaction in the precatalyst (4) and third means (5) for causing an exothermic reaction in the catalyst (8) so as to distribute the generation of the temperature rise of the exhaust gas, required by the regeneration of the particulate filter (9), between the engine (1), the pre-catalyst (4) and the catalyst (8).

2. Exhaust line according to claim 1, characterized in that the degradation of the combustion efficiency is obtained by under-setting the main fuel injection, that is to say by a later injection compared with at the top dead center (TDC) of the cycle.

3. Exhaust line according to claim 2, characterized in that the main injection is delayed by 2 to 20 ° crank angle relative to a normal injection.

4. Exhaust line according to claim 1, characterized in that the degradation of the combustion efficiency is obtained by reducing the amount of air admitted into the engine.

5. Exhaust line according to one of the preceding claims, characterized in that the means for generating an increase in the temperature of the gas output of the engine (1) make it possible to obtain, upstream of the pre-catalyst (4) a gas temperature of between 200 and 650 ° C.

6. Exhaust line according to one of the preceding claims, characterized in that the means for causing an exothermic reaction in the pre-catalyst (4) are able to trigger a post-fuel injection phase in the engine.

7. Exhaust line according to claim 6, characterized in that the post injection is late and between 90 to 240 ° angle of the crankshaft.

8. Exhaust line according to one of the preceding claims, characterized in that the temperature of the exothermic reaction in the pre-catalyst (4) is between 20 and 200 ° C.

9. Exhaust line according to one of the preceding claims, characterized in that the means for generating an exothermic reaction in the catalyst (8) is a fuel introduction device (5) disposed between the precatalyst (4) and the catalyst (8).

1 0. Exhaust line according to one of the preceding claims, characterized in that the temperature of the exothermic reaction in the catalyst (8) is between 20 and 300 ° C.

1 1. Exhaust line according to one of the preceding claims, characterized in that the three means for heating the exhaust gas are activated successively as a function of the difference between the temperature of the gases at the outlet of the engine and that necessary for the upstream of the particulate filter to ensure the regeneration thereof.

1 2. Exhaust line according to one of claims 1 to 1 0, characterized in that at least two means of heating the exhaust gas are activated simultaneously.

3. Exhaust line according to claim 1 2, characterized in that the two exothermic reaction are produced simultaneously and controlled so as to ensure the best compromise treatment HC / fuel consumption.

14. Exhaust line according to one of the preceding claims, characterized in that at high speed of the engine and medium and high load, the means for generating an increase in the temperature of the gas output of the engine are made preponderant compared to two other means for heating the gases.

5. The exhaust line according to one of the preceding claims, characterized in that the control of the heating means is predetermined by mapping.

6. Exhaust line according to one of claims 1 to 14, characterized in that the control of the heating means is a closed-loop control.

7. The exhaust system according to claim 1 6, characterized in that the control uses one or more sensed temperatures per sensor at different points in the exhaust line.

8. Exhaust line according to one of claims 1 6 or 1 7, characterized in that the regulation of the means generating the exothermic reactions takes into account the flow of gas exhaust.

1 9. Exhaust line according to one of claims 1 6 to 1 8, characterized in that when the means for generating an increase in the temperature of the gas output of the engine (1) operate by sub-calibration of the injection the main effect of the regulation is the sub-setting angle of the latter.

20. Exhaust line according to one of claims 6 to 1 9, characterized in that to regulate the exothermic reaction on the pre-catalyst (4) is adjusted the amount and phasage of the post-injection.

21. Exhaust line according to one of claims 9 to 20, characterized in that to control the exothermic reaction on the catalyst (8), it controls the average flow of fuel injected into the exhaust.

22. Exhaust line according to one of the preceding claims, characterized in that, to ensure the control of the strategy of the gas temperature rise, the control modes predetermined by mapping and closed-loop control are combined .

23. Exhaust line according to claim 22, characterized in that a cartographic control of the motor heating is coupled to a regulation by sensor for exothermic reactions in the pre-catalyst and in the catalyst.

24. Exhaust line according to one of the preceding claims, characterized in that, during the regeneration phase, the exhaust gas heating means are used continuously.

25. Exhaust line according to one of claims 1 to 23, characterized in that, during the regeneration phase, the exhaust gas heating means are used intermittently.

26. Exhaust line according to one of claims 1 to 23, characterized in that, during the regeneration phase, the exhaust gas heating means are used in continuously variable amounts.

27. Exhaust line according to one of the preceding claims, characterized in that the catalyst (8) is located upstream of the particulate filter (9).

28. Exhaust line according to one of claims 1 to 26, characterized in that the catalyst (8) and the particulate filter (9) are integrated on the same support.

29. Exhaust line according to one of the preceding claims, characterized in that the fuel comprises an additive to aid the regeneration of the particulate filter.