Desulfurization process for a nitrogen oxide trap in aftermarket use

Abstract

This process for desulfurizing a nitrogen oxide trap (1) in a motor vehicle comprises the following steps: Engine warm-up (step 11); Regeneration (step 12) of a particulate filter (3) located after the nitrogen oxide trap (1), until the soot mass (C) in the particulate filter (3) is lower than a predetermined mass; At least one pass (step 13) through a reducing medium with a richness (H) greater than 1, and heating of the nitrogen oxide trap (1) to a temperature (T) above 600°C until the sulfur mass (D) is lower than a critical sulfur mass threshold; Deoxidation (step 14) of the nitrogen oxide trap (1); Cooling (step 15) of the vehicle's mechanical components. Figure for the abbreviated version: Fig 2

Description

Description Title of the invention: Desulfurization process for an oxide trap nitrogen in after-sales service technical field

[0001] — The invention relates, in general, to methods of depolluting engines Internal combustion of motor vehicles, more specifically of internal combustion engines incorporating a hybrid system (for example with a 48-volt battery) and a grid heated exhaust.

[0002] = The invention relates in particular to the desulfurization of nitrogen oxide traps, particularly those of diesel engines.

[0003] — The invention also applies to any other type of vehicle requiring a desulfurization of nitrogen oxide traps for the proper functioning of these traps. Previous techniques

[0004] In the field of pollution control of internal combustion engines of vehicles at- vehicles, particularly diesel engines, require nitrogen oxide traps. mounted on engine exhausts to reduce the amount of nitrogen oxides contained in exhaust gases, the latter being harmful to the environment and health. This nitrogen oxide post-treatment trap puts in work of chemical reactions designed to transform oxides by reduction nitrogen (NOx) into neutral gases.

[0005] — However, the effectiveness of this treatment is impacted by sulfur, more specifically Sulfur oxides, also stored in the trap. The sulfur originates from the combustion of fuel when it has a high sulfur content or Engine oil consumption. Increased sulfur content in the trap nitrogen oxides cause a subsequent decrease in the effectiveness of the post- Exhaust gas treatment to reduce nitrogen oxides. It was therefore born- it is necessary to remove this sulfur through a desulfurization process.

[0006] — Desulfurization requires, among other things, maintaining the trap under conditions specific temperatures, which must be above 600°C, and to carry out the chemical reduction reactions with high richness, greater than 1, for which the amount of fuel is greater than the theoretical amount needed the complete combustion of the fuel in the mixture injected into the cylinders of Combustion with the amount of air present. Post-treatment of effluents Furthermore, the gas exchange must be carried out under specific engine operating or load conditions. particulars.

[0007] — This desulfurization process is intended to be repeated during certain phases of vehicle operation. However, if the vehicle is subjected, for example, to exclusively urban driving, under light load, with frequent stops and at low temperatures, the engine operating or load conditions may not be met often enough to perform desulfurization, so that under these conditions, sulfur accumulates in the nitrogen oxide trap, requiring its replacement at the dealership. Description of the invention The present invention therefore aims to overcome the aforementioned disadvantages and to facilitate the desulfurization of a nitrogen oxide trap of a thermal engine of a motor vehicle in after-sales service, that is to say when the vehicle has been acquired and requires intervention by the manufacturer. It concerns the now common case where the vehicle incorporates a hybrid system, that is, an electric machine capable of operating as a motor or as a generator to power the vehicle. More specifically, it concerns the case where this electric machine is mounted upstream of the vehicle's transmission system, typically a starter-alternator for the internal combustion engine. The present invention relates to a desulfurization process for a nitrogen oxide trap in a hybrid motor vehicle's internal combustion engine comprising an electric traction motor mounted upstream of the vehicle's transmission chain, characterized in that it is implemented when the vehicle is stationary, and in that it comprises the following steps: Starting the internal combustion engine; Regeneration of a particulate filter placed after the nitrogen oxide trap, until a soot mass is reached that is less than a predetermined mass in the particle filter; At least one passage through a reducing environment with a richness of function- operation of the internal combustion engine greater than 1, and heating of the trap nitrogen oxides up to a temperature above 600°C until reaching a mass of sulfur below a critical sulfur mass threshold, the the torque of the internal combustion engine being regulated by the electric traction motor; Deoxidation of the nitrogen oxide trap; Cooling of the vehicle's mechanical components. Thus, the process does not require replacing the nitrogen oxide trap and allows for its rapid purging of sulfur. This results in cost savings for both the vehicle owner and the manufacturer. Furthermore, the procedure is autonomous, performed by the vehicle's computer and an aftermarket software tool that connects to the computer to initiate the process. and requires no mechanical intervention on the engine. Furthermore, the process can be implemented using only the components already present in the vehicle. It requires no additional parts during vehicle construction other than those necessary for its normal operation. Advantageously, each stage is performed at a specific engine speed and load of the internal combustion engine. The load, i.e., the torque, is regulated by the electric motor, to which positive or negative torque commands are applied. It is therefore essential that the electric motor be located upstream of the vehicle's transmission system to enable this regulation of the internal combustion engine's torque. According to one embodiment, the process uses a heating grid, an alternator-starter, an electric battery and means for increasing or decreasing the richness of the air and fuel mixture in the heat engine configured to regulate the temperature, speed or load conditions of the heat engine for the desulfurization of the nitrogen oxide trap. Advantageously, the state of charge of the vehicle's battery is regulated by regulating the engine load via the alternator-starter. Advantageously, during the particulate filter regeneration stage, the filter temperature is increased by means of a heating element, up to a temperature suitable for burning the soot. According to one implementation method, the particulate filter regeneration stage is carried out with a fuel injection delay in order to increase the exhaust temperature. During this process, the fuel-air mixture is enriched compared to normal engine operation, but it is known that it remains below 1. The invention also relates to a data processing system comprising means for implementing the steps of the process defined above. Brief description of the drawings 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: [fig.1] schematically illustrates different elements of a motor vehicle implemented in a desulfurization process according to the invention; [fig.2] illustrates the different stages of the process according to the invention as well as the evolution over time of the different parameters involved in the desulfurization process. Detailed description of at least one embodiment A simplified diagram representing different elements is shown in [fig.1] of a motor vehicle involved in a vehicle aftertreatment system for gaseous effluents implementing the invention. The motor vehicle is a hybrid vehicle equipped with an internal combustion engine, for example of the diesel type and an electric traction motor mounted upstream of the vehicle's transmission chain, capable of regulating the torque delivered by the internal combustion engine. In one implementation of the process, the electric motor is an alternator-starter of the internal combustion engine, which is linked to the output shaft (crankshaft) of the internal combustion engine and which is capable of adding electrical torque to this output shaft or of taking torque from it by acting in a generator mode. The vehicle aftertreatment system includes, in particular, a nitrogen oxide trap, a data processing system 2, a particulate filter 3 located downstream of the nitrogen oxide trap 1, and various sensors and probes 4 upstream and downstream of the nitrogen oxide trap to perform measurements, for example, of fuel mixture. The data processing system 2 is, for example, the vehicle's on-board computer. It includes all the necessary hardware and software and is duly programmed to implement the desulfurization process according to the invention. It is connected, in particular, by wired or wireless link to the aftertreatment system itself. The process is initiated by connecting an aftermarket computer tool to the computer. A heating element 5, for example a heating grid, connected to a battery 8 for its power supply, is positioned upstream of the nitrogen oxide trap 1. The alternator-starter 6 is connected to the engine's crankshaft 7 and to the battery 8, for example a 48-volt battery, which stores electrical energy generated when the alternator-starter 6 operates in generator mode and draws torque from the crankshaft 7. Conversely, the battery 8 discharges when the alternator-starter 6 operates in motor mode and consumes energy. In motor mode, the energy consumed by the alternator-starter is used to increase the torque at the engine shaft output, or to power the heating grid S via the battery 8, which acts as a buffer. The post-treatment system implements a desulfurization process in order, in particular, to remove sulfur, more specifically sulfur oxides which result from the combustion of the fuel and which are trapped in the nitrogen oxide trap 1. Figure 2 illustrates the different stages of the nitrogen oxide trap desulfurization process according to the invention, as well as the evolution over time t of the various parameters involved in the process. The parameters shown are the internal temperature T of the nitrogen oxide trap 1, the mode A of the alternator-generator 6 (motor or generator), the charge B of the battery 8, and the mass C of soot in the filter. particle 3, the mass D of sulfur oxides in the nitrogen oxide trap 1, the mass E of nitrogen oxides in the nitrogen oxide trap 1, the engine speed F, the activation G or not of the heating grid, and the richness H of the air-fuel mixture. Firstly, when the mass D of sulfur oxides becomes too high, and therefore critical, within the nitrogen oxide trap 1, the vehicle driver is alerted, for example by a warning light on the vehicle's dashboard. The critical sulfur mass threshold can be calibrated, for example with a threshold of a few grams per liter, depending on the volume of the nitrogen oxide trap 1, which is generally 1 to 3 liters. The warning light indicates that the aftertreatment system is faulty and that the vehicle must be taken to a dealership for servicing and desulfurization of nitrogen oxide trap 1. At the dealership, an after-sales computer tool, or supervisor, first checks the severity of the trapped sulfur oxide mass, for example, via a diagnostic port, with the engine off. The supervisor also checks for any other faults that could affect the desulfurization process. It then initiates the actual process, which is carried out by the vehicle's onboard computer. The process begins with a first step 11 of warming up the engine. This first step lasts, for example, less than 10 minutes and is carried out at a predefined engine speed F and load. For example, the engine speed F is 2000 revolutions per minute and the engine load corresponds to a torque of 100 Newtons. Stage 11, the warm-up phase, raises the temperature of the engine components, the exhaust system, and various fluids circulating in the vehicle's powertrain (engine and transmission). For example, stage 1 of the warm-up phase raises the coolant temperature to a minimum of 40° to 60°C. The process then includes a step 12 of regeneration of the particulate filter 3. This step is carried out at a predefined engine speed F and engine load and allows the soot present in the particulate filter 3 to be burned down to a mass C below a predefined mass, for example below 6 grams per liter, the particulate filter 3 having a volume of 2 to 5 liters. Soot must be removed from the particulate filter 3 to prevent thermal runaway and maintain the integrity of the particulate filter 3 during the subsequent desulfurization step 13. This desulfurization step 13 is carried out at high temperatures T, on the order of 650° to 750°C in the nitrogen oxide trap 1, which promotes thermal runaway if excessive soot is present in the particulate filter 3 and a significant oxygen supply is also introduced. The temperature T for performing step 12 of particulate filter 3 regeneration and Burning soot is approximately 500° to 600°C. Stage 12 of regeneration and temperature rise are carried out for example by degrading the combustion efficiency of the engine by a delay in fuel injection, by an input of reducers (fuel) in the exhaust line but also of oxidants (oxygen) to burn the soot and by the use of the heating grid 5. The additives include fuel injected via post-injection, which does not participate in combustion within the engine's combustion chambers but burns on the nitrogen oxide trap in the presence of oxygen. The heating grid 5 uses the energy stored in the battery 8 to increase the temperature T in the exhaust line near the emissions control system. This allows, on the one hand, the battery 8 to be depleted for the subsequent stage 13 and, on the other hand, to reduce the amount of fuel injected via post-injection. In this stage 12, the air-fuel ratio H is higher than the engine's normal operating ratio but remains below 1, in order to ensure sufficient oxygen is available to oxidize the post-injection fuel. When the soot mass C is below the predefined mass threshold, for example after 10 minutes of the particulate filter regeneration stage, the desulfurization stage 13 begins. Meanwhile, the temperature T in the nitrogen oxide trap continued to increase during the end of regeneration stage 12 until reaching a minimum temperature T of 600°C, preferably between 650° and 750°C. Stage 13 is the stage during which the mass of sulfur in the nitrogen oxide trap 1 decreases. It is also called the desulfurization stage and takes place at a predefined engine speed (F) and load (favorable to efficient sulfur treatment). This is a relatively high engine speed and load compared to urban driving conditions, which are unfavorable to desulfurization. During this step 13, it is necessary to operate in a reducing environment, with a fuel-air ratio greater than 1, and to maintain a high temperature T, for example, between 650° and 750°C. However, operating in a reducing environment for too long can be very thermally demanding on the emissions control system. Therefore, in order to maintain its integrity, it is necessary to alternate the engine settings in the cylinder between a fuel-air ratio H strictly greater than 1, for example, between 1.05 and 1.10, and a fuel-air ratio H lower than the previous one, which may even be less than 1, for example, between 0.9 and 1.1. This alternation allows the nitrogen oxide trap 1 to cool down. In order to easily regulate the temperature in the nitrogen oxide trap 1, the heating grid 8 is used temporarily, for example, to maintain a high temperature range T between 700° and 750°C. During desulfurization stage 13, the engine load or torque must be above a certain threshold to allow these high-rich settings. This load also increases the temperature T in the nitrogen oxide trap 1. The load is regulated (increased) using the alternator-starter 6 to ensure efficient sulfur removal. The alternator-starter 6 then operates in generator mode A and stores the additional energy in the battery 8, which had been partially discharged during stage 12 of particulate filter 3 regeneration. Concurrently, if the battery 8 is fully charged, the heating grid 5 is activated to increase the temperature T and discharge the battery 8. Once the sulfur mass D falls below the critical sulfur mass threshold, approximately after 25 minutes, a deoxidation step 14 of the nitrogen oxide trap 1 is performed at a predefined engine speed F and load. Indeed, the high temperatures T of the preceding steps and the oxygen supply have generated oxidation in the nitrogen oxide trap 1, which alters its storage and directly impacts exhaust emissions. This deoxidation step 14 is carried out with a combustion mode at an H-equivalent air-fuel ratio greater than 1. As with the previous step 13, alternating between H-equivalent and H-equivalent ratios is necessary to avoid excessively high temperatures T. This step 14 thus reduces the nitrogen oxide mass E to a predefined mass, for example, a few grams per liter in the nitrogen oxide trap 1. Finally, a last step 15 involves cooling the vehicle to ensure it is returned to the driver without risk of thermal injury. For example, the cooling process is considered complete when the temperature T of the nitrogen oxide trap 1 has returned to the initial temperature of the process. The entire process takes approximately one hour. During all the preceding stages, the alternator-starter 6 operates, or can operate, in generator mode (A) or in engine mode to reach a specific engine speed (F) or load, or to recharge the battery (8). Similarly, the heating grid (5) regulates the temperature during each stage, or consumes energy from the battery (8) to subsequently allow the alternator-starter to operate in generator mode to increase the torque of the internal combustion engine. To achieve this, control loops are implemented using sensors to measure each parameter and trigger the activation of the heating grid (5), the alternator-starter (6), a fuel mixture adjustment (H), or any other device used to regulate these parameters. The invention is not limited to the embodiment just described. For example, in one implementation method, it is the driver himself who, a Once the vehicle is stopped, the desulfurization procedure can be initiated by following the steps indicated by the manufacturer via a button on the dashboard or a dedicated menu in the on-board computer. In another implementation mode, the vehicle's engine is equipped with a gasoline engine.

Claims

Demands

1. Method for desulfurizing a nitrogen oxide trap (1) in an engine hybrid motor vehicle thermal system comprising an engine of electric traction mounted upstream of the transmission chain of the vehicle, characterized in that it is implemented when the vehicle is at a standstill, and in that it comprises the following steps: Warming up the internal combustion engine (step 11); Regeneration (step 12) of a particulate filter (3) placed after the nitrogen oxide trap (1), until a mass (C) is reached soot less than a predetermined mass in the filter particles (3); At least one passage (step 13) in a reducing medium with a richness (H) of operation of the internal combustion engine su- greater than 1, and heating of the nitrogen oxide trap (1) up to a temperature (T) above 600°C up to to reach a mass (D) of sulfur below a threshold of critical sulfur mass, the torque of the heat engine being regulated by the electric traction motor; Deoxidation (step 14) of the nitrogen oxide trap (1); Cooling (step 15) of the mechanical components of the vehicle.

2. Method according to claim |, characterized in that it is put into works only with the components already present in the vehicle.

3. A method according to any one of claims 1 and 2, wherein each step is carried out at a specific engine speed (F) and load.

4. A method according to any one of claims 1 to 3, characterized in what it uses a heating grid (5), an alternator-starter (6), a battery (8) and means of increasing or decreasing the richness (H) of the air and fuel mixture in the internal combustion engine configured to regulate temperature (T) and operating conditions (F) or thermal engine charge for trap desulfurization (1) to nitrogen oxides.

5. A method according to claim 4, wherein the state of charge is regulated of the vehicle's battery (8) by regulating the motor's charge by the alternator-starter (6).

6. A method according to any one of claims 1 to 5, wherein during step (12) of regeneration of the particulate filter (3), we increases the temperature of the particulate filter (3) by means of a re- heating element, up to a temperature suitable for burning the alone.

7. A method according to any one of claims 1 to 6, wherein step (12) of regenerating the particulate filter (3) is carried out with a fuel injection delay in order to increase the richness (H) to a level below 1.

8. Data processing system (2) comprising means for implement the steps of the process according to any one of the re- demands 1 to 7.