FR2930968A1 - METHOD FOR REGENERATING A POST PROCESSING SYSTEM BY FRACTIONING WEALTH - Google Patents

Abstract

The invention relates to a method for regenerating a gas post-treatment system of an exhaust line 1 of an internal combustion engine 2 by raising the temperature of the post-treatment system to a regeneration temperature. . During the rise in temperature, the richness of the air / fuel mixture is varied by implementing successive phases of injection of relatively rich and poor mixtures independently of the consumption or the renewal of oxygen in the exhaust line. .

Description

B 07/3115 EN ùEHE / ODE Project 7561

Simplified joint-stock company known as: RENAULT s.a.s

A method of regenerating a post-processing system by fractionating wealth. Invention of: GIRODON Alain Regeneration process of a post-processing system by fractionation of wealth.

The present invention generally relates to aftertreatment systems for the exhaust gases of an internal combustion engine, in particular a diesel engine, and, in particular, the regeneration of the after-treatment systems. In order to meet the lower thresholds for emissions of gaseous pollutants from motor vehicles, more and more complex post-treatment gas systems are placed in the exhaust line of internal combustion engines. These include reducing emissions of particulates and nitrogen oxides in addition to carbon monoxide and unburned hydrocarbons. To completely burn the pollutants, these post-treatment systems require working at high temperatures, which is unfortunately not the case under normal engine conditions. When considering a regeneration phase of a particulate filter to prevent clogging thereof, the desulfurization of a nitrogen oxide trap, or more generally the treatment of pollutants with a high temperature, a point is chosen. of engine operation favorable to the regeneration process. The regeneration is preceded by a heating phase of the system in order to obtain the minimum temperature above which it is effective. Two types of strategies exist. A first strategy uses preheating systems such as air pumps, electrical resistors, an additional injector to the exhaust, while another strategy optimizes the operation of the engine to increase the temperature of the exhaust gas.

For example, GB 2324052 A (Ford) discloses a method of regenerating a post-treatment system comprising a three-way catalyst and a nitrogen oxide trap connected in series, the nitrogen oxide trap containing storage elements for oxygen. The method consists of controlling the richness of the air / fuel mixture of the engine during the temperature rise phase as a function of the oxygen consumption and renewal cycles in the nitrogen oxide trap. A relatively poor mixture is injected for a time sufficient for the oxygen to be stored in the nitrogen oxide trap. A relatively rich mixture is then injected into the cylinders for a sufficient time so that the resulting surplus of fuel in the exhaust gas first reacts completely with the oxygen stored in the three-way catalyst, and then the surplus remaining fuel passes through the three-way catalyst to react with the oxygen stored in the nitrogen oxide trap, thereby releasing heat and raising the temperature of the nitrogen oxide trap.

The amplitude of modulation of the air / fuel ratio necessary for this operation is of the order of X = 0.1 and the frequency must be smaller than 1 Hz. This mode of operation must be maintained for approximately 5 minutes before the trap nitrogen oxide does not reach the regeneration temperature. The engine must also be maintained in an operating mode in which excess fuel is obtained for a period of time long enough to purge the trap. The patent application US 2005/0076637 (Audi) describes another type of regeneration process of an exhaust line in which a lean air / fuel mixture is introduced into the internal combustion engine, by additionally injecting fuel. in the combustion chamber of the engine after the primary injection. The richness of the air / fuel mixture of the engine is cyclically modulated during the temperature rise phase by following the cycles of consumption and renewal of oxygen in the catalyst. Moreover, the probability of maintaining favorable purging conditions is inversely proportional to the heating time of the post-treatment system. Therefore, whatever the heating strategy used, the objective is to reach as quickly as possible the temperature from which the post-treatment system is effective in order to increase desulfurization opportunities and to limit the dilution of fuel in the oil.

In order to obtain the necessary conditions of richness and temperature upstream of the system, one method consists of injecting fuel into the combustion chamber, creating no torque, after the top dead center, while maintaining a richness (air mixture / fuel) below 1. Indeed, the fact of increasing the richness of the gases causes a rise in temperature and exotherm in the catalytic part of the post-treatment systems, due to the oxidation of the poorly mixed reducing agents (air / fuel ratio greater than 1). The level of richness (Ri = 0.99) is then kept constant during the heating period.

In practice, it is found with this method that the heating times of a nitrogen oxide trap are too high at low speed and low loads, since they are of the order of 50 to 100 seconds, which is not acceptable on urban and extra-urban type rolling profiles since they do not make it possible to carry out effective desulfurization and generate a high dilution.

The invention thus aims to accelerate the temperature rise of the aftertreatment systems present at the exhaust by acting directly on the richness of the gas output of the engine. The subject of the invention is therefore a method for regenerating a gas post-treatment system of an exhaust line of an internal combustion engine by raising the temperature of the post-treatment system to a temperature regeneration. According to a general characteristic of this process, during the rise in temperature, the richness of the air / fuel mixture is varied by implementing successive phases of injection of relatively rich and poor mixtures independently of the consumption and the renewal of oxygen in the exhaust line. Advantageously, for each of the rich / poor cycles of the temperature rise phase up to the regeneration temperature, the relatively rich mixture remains established for a time within a range of 0.5s to 2s, and the relatively poor mixture remains established during a time in the same interval from 0.5s to 2s. This time is previously defined, and does not require additional sensors that would add to the cost of production. Advantageously, during this rise in temperature, the increase in richness of the mixture at each new cycle can be done for example by injecting fuel upstream of the post-treatment system. It is also possible to increase the richness of the air / fuel mixture by post-injection of fuel into the engine, that is to say by performing a delayed injection of fuel into the engine cylinders, so that this additional fuel injected is not burned and contributes to the rise of wealth, and thus the rise in temperature. According to one embodiment, for a motor operating point stabilized at 1200 rpm / 4 bar, the wealth richness slot X = 1.01 (poor) and wealth richness X = 0.95 (rich) are fractionated. duration 1 second. Another subject of the invention is a gas post-treatment system of an exhaust line of an internal combustion engine comprising means for raising the temperature of the post-treatment system to a maximum of regeneration temperature. According to a general characteristic of this system, it comprises means for varying the richness of the air / fuel mixture and means for implementing successive phases of injection of relatively rich and poor mixtures regardless of consumption or renewal of oxygen in the exhaust line to raise the temperature of the post-treatment system to the regeneration temperature. Advantageously, the system may comprise an additional fuel injector placed at the inlet of the aftertreatment system intended to increase the richness of the air / fuel mixture during a purge phase of the post-treatment system. According to one characteristic of the invention, the device comprises a temperature probe placed between the nitrogen oxide trap and the particle filter. According to yet another characteristic of the invention, the device comprises a temperature probe at the input of the post-treatment system.

This temperature probe is placed between the additional injector and the nitrogen oxide trap, as close as possible to the trap, in the case of an additional injector enrichment system. It is also possible to use a system for measuring the differential pressure at the level of the particulate filter for controlling the state of the filter. Advantageously, the device of the invention comprises an oxygen probe placed at the outlet of the nitrogen oxide trap. This oxygen sensor placed downstream of the nitrogen oxide trap makes it possible to detect the purges of the trap and to check the state of said trap during onboard diagnostics. Advantageously, the device of the invention comprises an oxygen probe placed upstream of the nitrogen oxide trap. This oxygen sensor is also placed upstream of the additional injector in the case of a wealth increase by additional injector. This oxygen sensor, which makes it possible to measure the fractionation of the richness of the air / fuel mixture upstream of the additional injector, makes it possible to construct a setpoint by estimation for the control relating to the operation of the nitrogen oxide trap. Other advantages and characteristics of the invention will appear on examining the detailed description of an embodiment of the invention which is in no way limitative, and the attached drawings, in which: FIG. 1 illustrates the evolution of the temperature on the upstream face of a nitrogen oxide trap during a rich / poor transition of the exhaust gas of an internal combustion engine. FIG. 2 illustrates a post-processing architecture implementing the regeneration method according to the invention. FIG. 3 represents curves of temperature and of dilution of the fuel in the oil as a function of time, in the case of a conventional heating with constant richness X = 1.01. FIG. 4 represents curves of temperature and dilution of the fuel in the oil as a function of time, in the case of heating by rapid fractionation of the richness. FIG. 1 shows the temperature variation of a monolith (cl), during a test phase, at low hourly volumetric speed, during a rich / poor transition. During the rich / poor transition (Trp), the temperature of the monolith increases before decreasing towards the stabilized temperature of the poor state. This phase is exploited to increase the heating rate of the monolith. By quickly splitting the richness into two rich and poor niches, the heating of the monolith is optimized, unlike a heating of the post-processing system realized at a constant richness of the order of X = 0.99. It is therefore possible with this strategy to reduce the heating time in the order of 50% under difficult driving conditions, that is to say at low speed and low load. This reduces the heating time and the dilution of the fuel in the oil, thus optimizing the overall management of benefits depollution / consumption and dilution of diesel in the oil. FIG. 2 represents an architecture according to the invention, designated by the general numerical reference 1, intended for the post-treatment of the exhaust gases and therefore intended to be placed at the outlet of an internal combustion engine 2. As can be seen , the exhaust gases are discharged by the post-treatment system here composed of a nitrogen oxide trap 3 and a particulate filter 4. The temperature of the post-treatment system is controlled at the inlet by a first temperature probe 5 and the input of the particle filter with a last temperature probe 6. The state of the nitrogen oxide trap and therefore the need or not to regenerate the trap is controlled using an oxygen probe 7 placed at the exit of the trap. The particulate filter clogging is controlled by a system for measuring the differential pressure 9 between the inlet of the particulate filter and its outlet. In order to raise the richness of the gases in the aftertreatment system, an additional fuel injector 10 is placed at the inlet of the nitrogen oxide trap in this example. The richness of the mixture can also be achieved by post-injection of fuel into the cylinders. The fractionation of the richness of the air / fuel mixture is measured by means of an oxygen sensor 13 placed upstream of the nitrogen oxide trap 3 and the additional fuel injector 10.

A duly programmed electronic control unit 12 controls the main injection system and, in particular, monitors the fouling of the after-treatment systems, that is to say the particle filter from the differential pressure. prevailing on both sides of the filter. When it is detected that the filter needs to be regenerated, the filter temperature is raised to a regeneration temperature. This temperature rise is for example obtained by injecting an air / fuel mixture into the exhaust line by means of the injector 10. At low hourly volumetric speed, during a rich / poor transition, the temperature in a monolith starts to increase before decreasing towards the stabilized temperature of the lean state. Thus, the temperature rise is here obtained by exploiting this temperature increase phase preceding the lowering of temperature in order to increase the heating rate of the filter. By quickly splitting the richness into two rich and poor niches unlike the initial situation where the heating of the post-treatment system was carried out at a constant richness of the order of X = 0.99, the heating of the monolith is optimized. . It is therefore possible with this new strategy to reduce the heating time in the order of 50% under difficult driving conditions, that is to say at low speed and low load. This reduces the heating time and the dilution of the fuel in the oil, thus optimizing the overall management of benefits depollution / consumption and dilution of diesel in the oil.

For example, on a motor operating point stabilized at 1200 rpm / 4 bar, we split the richness of wealth wealth X = 1.01 (poor) and richness X = 0.95 (rich) duration of 1 second, unlike in the state of the art where the regeneration occurs traditionally with a constant richness of the exhaust gas value X = 1.01 throughout the heating period of the post-treatment system. Figure 3 shows the temperature (c2) and dilution (c3) curves of the fuel in the oil as a function of time, in the case of conventional constant-flow heating X = 1.01, while Figure 4 represents the temperature (c2 ') and dilution (c3') curves of the fuel in the oil as a function of time, in the case of fractionation heating according to the invention of the richness. It is noted that after 40s of heating, the temperature on the upstream face of the nitrogen oxide trap reaches 658 ° C in fractional mode, whereas it reaches only 564 ° C in constant rich mode, which represents a 96 ° C gain. If we consider the heating time to reach 564 ° C on the upstream face of the nitrogen oxide trap, just 23s in fractional heating instead of 40s constant wealth is a gain of 17s.

From a point of view of fuel dilution in oil, the curves also show a gain on the integral of the quantity of fuel post injected. At the iso heating temperature, here 564 ° C, the cumulative amount of fuel post injected is only 313 cg s / cp in fractional mode instead of 363 cg s / cp heating constant wealth, this which represents a gain of 15%. Thus, as illustrated by the previous curves, it takes less time than for the prior art to achieve the same temperature setpoint, while injecting less fuel into the post injection. This reduces the diesel fuel dilution and the fuel consumption of the motor vehicle. It will be noted that the regeneration method which has just been described can be adapted to any post-treatment architecture provided with a nitrogen oxide trap, a particle filter, an additional injector, of a pre-treatment temperature probe and an inlet temperature sensor of the particulate filter, an oxygen sensor at the exit of the nitrogen oxide trap, a differential pressure sensor at the level of particle filter, and an electronic control unit driving these elements.

Claims (12)

REVENDICATIONS1. A method of regenerating a gas post-treatment system of an exhaust line (1) of an internal combustion engine (2) by raising the temperature of the after-treatment system to a regeneration temperature, characterized in that during the rise in temperature the richness of an air / fuel mixture is varied by implementing successive phases of injection of relatively rich and poor mixtures independently of the consumption or renewal of oxygen in the exhaust line. 2. Method according to claim 1, characterized in that for a time in a range of 0.5s to 2s, the relatively rich mixture remains established, and the relatively poor mixture remains established for a time in the same range of 0.5s to 2s, until said regeneration temperature is reached. 3. Method according to any one of claims 1 to 2, characterized in that the richness increase of the mixture is done by injecting fuel upstream of the post-treatment system. 4. Method according to any one of claims 1 to 2, characterized in that the richness of the mixture is achieved by post-injection of fuel into the engine. 5. A method according to any one of claims 1 to 4, characterized in that on a motor operating point stabilized at 1200 rpm / 4 bar, the wealth richness slot x is divided into 1.01 (poor) and of richness X = 0.95 (rich) of duration 1 second. 6. A device for regenerating a gas post-treatment system of an exhaust line (1) of an internal combustion engine (2) comprising means for raising the temperature of the post-treatment system to a maximum of regeneration temperature, characterized in that it comprises means for varying the richness of the air / fuel mixture and means for implementing successive phases of injection of relatively rich and poor mixtures regardless of consumption or renewal of oxygen in the exhaust line to raise the temperature of the post-treatment system to the regeneration temperature. 7. Device according to claim 6, characterized in that it comprises an additional fuel injector (10) placed at the inlet of the aftertreatment system (1) for increasing the richness of the air / fuel mixture when a purge phase of the post-processing system. 8. Device according to claims 6 and 7, characterized in that it comprises a temperature sensor (6) placed between the nitrogen oxide trap (3) and the particle filter (4). 9. Device according to any one of claims 6 to 8, characterized in that it comprises a temperature sensor (5) at the input of the post-processing system. 10. Device according to any one of claims 6 to 9, characterized in that it comprises a system for measuring the differential pressure (9) at the particle filter (4) for controlling the state of the filter. 11. Device according to any one of claims 6 to 10, characterized in that it comprises an oxygen sensor (7) placed at the outlet of the nitrogen oxide trap (3). 12. Device according to any one of claims 6 to 11, characterized in that it comprises an oxygen sensor (13) placed upstream of the nitrogen oxide trap (3).