CN101592090B - Method for reducing emission of diesel engine for light vehicle - Google Patents

Abstract

The invention discloses a method and a device for reducing the emission of a light-duty diesel engine. The method includes the following steps: (1) The control unit reads the rotation speed signal and the engine load signal respectively, and judges according to the signals whether the engine is running at medium load, low load or (2) If the judgment result in step (1) is medium or low load, the control unit sends an opening and closing signal to the supercharging control valve, and at the same time sends a working signal to the electromagnetic clutch, and the electromagnetic clutch and the crankshaft drive The system meshes to drive the supercharger and the turbocharger to work at the same time, and at the same time the control unit sends an opening signal to the back pressure valve and the exhaust gas recirculation valve; (3) If the judgment result in step (1) is the working condition of heavy load , the control unit sends an opening signal to the supercharging control valve, and the turbocharger works independently; at the same time, the control unit sends an opening signal to the back pressure valve and the exhaust gas recirculation valve. This method can meet the national 4/5 emission requirements.

Description

A Method for Reducing Emissions from Diesel Engines of Light Vehicles

technical field

The invention relates to a method and a device for reducing the emission of a diesel engine of a light vehicle. the

Background technique

The combustion process of diesel engine belongs to the diffusion combustion of spray. Because the mixing time of fuel spray and air is very short and the mixture is not uniform, a high-temperature over-rich zone and a high-temperature flame zone are formed during the combustion process. In the high-temperature and over-rich area, more soot is generated due to the oxygen-deficient atmosphere; while in the high-temperature flame area formed by combustion, a large amount of NOx is generated. The difference in the generation conditions of diesel engine soot and NOx makes the measures to reduce one kind of emission often lead to the increase of another kind of emission, that is, there is a trade-off relationship that is usually said to be a trade-off relationship between soot and NOx. The trade-off relationship between them is the key to reduce diesel engine emissions. the

From the point of view of the formation mechanism, soot is mainly generated in a certain temperature range where the mixture gas is relatively dense, and the concentration of the mixture gas is the most important factor affecting soot; while NOx is generated more when the temperature is greater than 2200K, and reducing the combustion temperature is to reduce NOx The most effective measure of emissions. The effective effect of exhaust gas recirculation on reducing NOx emissions has been widely recognized, but in practice it often leads to an increase in soot emissions. The reduction effect of exhaust gas recirculation on combustion temperature and the dilution effect on intake air (reduction of oxygen concentration) are the main factors to reduce the formation of NOx, but the exhaust gas recirculation generally reduces the fresh air entering the cylinder, causing the mixture to become richer. The reduction in combustion velocity and temperature also slows down the oxidation of soot, resulting in increased soot emissions. Therefore, when adopting exhaust gas recirculation technical measures, how to maintain good soot emission is the key problem to be solved. the

The common working condition of light-duty vehicles is partial load condition, and the emission test working conditions are mainly distributed in medium and low load conditions (about 50% load and below). The air-fuel ratio of the engine is generally high at medium and low loads, and the negative impact on the smoke caused by the use of a small proportion of exhaust gas recirculation is relatively small. When it is high), it is necessary to take appropriate measures to increase the intake air volume to maintain a sufficient air-fuel ratio, so as to ensure good soot emission while effectively reducing NOx emissions. the

Contents of the invention

The object of the present invention is to overcome the deficiencies of the prior art and provide a method and device for reducing the emission of light-duty diesel engines to meet the emission requirements of the national standard 4 and national 5 stages. the

A kind of method that reduces light vehicle diesel engine emission of the present invention, it comprises the following steps:

(1) The control unit reads the speed signal of the sensor installed on the engine crankshaft and the engine load signal of the sensor installed on the accelerator pedal respectively, and judges whether the engine is running at medium or low load according to the speed signal and engine load signal The working condition is still running under the heavy load condition;

(2) If the judgment result in step (1) is the working condition of medium and low load, then the control unit sends a closing signal to the supercharging control valve installed on the engine intake pipeline, and sends a working signal to the electromagnetic clutch at the same time. signal, the electromagnetic clutch is engaged with the crankshaft drive train to drive the supercharger and the turbocharger to work simultaneously, and the control unit sends The pressure valve and the exhaust gas recirculation valve of the exhaust gas recirculation pipeline send out opening degree signals;

(3) If the judgment result in step (1) is a heavy load working condition, then the control unit sends an opening signal to the mechanical supercharging control valve installed on the intake pipeline, and simultaneously sends a disconnection signal to the electromagnetic clutch, The turbocharger works independently; at the same time, the control unit sends opening degree signals to the back pressure valve installed on the exhaust pipe of the engine and the exhaust gas recirculation valve of the exhaust gas recirculation line according to the calibrated control map. the

The device for reducing light-duty diesel engine emissions of the present invention comprises an exhaust gas turbocharging system equipped with an exhaust gas turbocharger, an exhaust gas recirculation system, a two-stage oxidation reactor, and it also includes a supercharging system, and the mechanical The supercharger system includes a supercharger control valve installed on the engine intake pipeline, a supercharger connected in parallel with the supercharger control valve, and a rotating shaft of the supercharger is connected with the first belt drive train , a second belt drive train is connected to the crankshaft of the engine, an electromagnetic clutch is installed between the first and second belt drive trains, and the two-stage oxidation reactors are respectively installed in the exhaust gas turbocharger On the front and rear engine exhaust pipes. the

The light-duty vehicle diesel engine emission control method of the present invention mainly includes a compound supercharger system (composed of a common turbocharger and a mechanical supercharger), an electronically controlled exhaust gas recirculation system, and a two-stage oxidation reactor (DOC). Processing device. In the common working conditions of light vehicles, the supercharger participates in the work, that is, the compound supercharging mode is adopted, which can greatly increase the supercharging pressure and intake air volume, and effectively reduce NOx emissions by controlling the exhaust gas recirculation rate and realizing low-temperature combustion. The sufficient amount of fresh air provided by the compound supercharger can also control the soot emission at a better level, and the two-stage DOC can meet the national 4/5 emission requirements. In heavy load conditions, ordinary turbochargers can work alone. the

Description of drawings

Fig. 1 is a kind of system schematic diagram of the method and device thereof that reduces light vehicle diesel engine emission of the present invention;

Fig. 2 is a control schematic diagram of the present invention. the

Detailed ways

The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments. the

As shown in Fig. 1, the device for reducing light-duty diesel engine emissions of the present invention includes an exhaust gas turbocharging system and an exhaust gas recirculation system. 10, exhaust gas turbocharger 1, air intake intercooler 11, the device of the present invention is equipped with a supercharging control valve 7 on the engine intake pipeline after the air cleaner 10. At present, the engine exhaust gas of the usual exhaust gas recirculation system is divided into two paths, one path communicates with the atmosphere, and a back pressure valve is installed on the exhaust pipe. The other path communicates with the engine intake pipe, and an exhaust gas recirculation cooler 9 and an exhaust gas recirculation valve 8 are installed in sequence on the exhaust gas recirculation pipe. The device of the present invention also includes a supercharging system, and the supercharging system includes the supercharging control valve 7 installed on the engine intake pipeline, and the supercharging control valve 7 connected in parallel with the supercharging control valve. Compressor 3, the rotating shaft of the supercharger 3 is connected with the first belt transmission system 5, and a second belt transmission system 6 is connected with the crankshaft of the engine, between the first and second belt transmission systems There is electromagnetic clutch 4. The two-stage oxidation reactors 12 and 13 are respectively installed on the engine exhaust pipes before and after the exhaust gas turbocharger 1 . the

A kind of method for reducing light vehicle diesel engine emission of the present invention as shown in Figure 1, 2, it comprises waste gas turbocharger 1, back pressure valve 2, supercharger 3, electromagnetic clutch 4, belt drive system 5 and 6. Supercharging control valve 7. Exhaust gas recirculation valve 8. During the running of the engine, the control unit receives the signals of the speed and the accelerator pedal (corresponding to the load of the engine), determines the operating conditions of the engine according to the above signals, and judges whether the supercharger is working. If the engine is running in the normal working condition of medium and low load, the electromagnetic clutch 4 is engaged with the crankshaft transmission system, and the rotational motion of the crankshaft is transmitted to the shaft system of the supercharger through the belt transmission system 5 and 6, and the supercharger starts to work , at this time, the supercharger control valve 7 is closed, and the intake air enters the cylinder of the engine after being supercharged by the supercharger and the exhaust gas turbocharger. At the same time, the control unit (ECU) The calibrated control map (MAP) map controls the opening of the exhaust gas recirculation valve 8 and the back pressure valve 2, so as to realize the control of the exhaust gas circulation rate (EGR) rate, and the calibration of the control map (MAP) map to control The NOx emission meets the national standard 4 or national 5 emission requirements for calibration. In this way, in partial load conditions, the EGR rate required for NOx emission control and sufficient intake air volume required for soot emission control can be guaranteed at the same time. In heavy load conditions, in order to reduce the mechanical load of the engine, the electromagnetic clutch 4 is disengaged from the crankshaft transmission system, the supercharger stops working, the supercharger control valve is opened, and the intake air bypasses the supercharger and directly enters the turbocharger. The inlet of the device, the engine is in the mode of single-stage supercharging, and at the same time, the control unit sends the opening degree to the back pressure valve and the exhaust gas recirculation valve installed on the exhaust pipe of the engine according to the calibrated control map (MAP) Signal, because the exhaust energy is relatively sufficient at this time, the exhaust gas turbocharger alone can also provide sufficient boost pressure and intake air volume, which can also ensure the performance and emission of the engine. At the same time, the two-stage oxidation reactor (DOC) aftertreatment system can further reduce particulate (soot) emissions, so that the high-efficiency and low-emission combustion process of light vehicle diesel engines can be realized. the

Example 1

Adopt the inventive method to carry out bench test to the light vehicle diesel engine that displacement is 2.7L:

The control unit reads the speed signal and the accelerator pedal signal respectively, and if it is judged according to the speed signal and the accelerator pedal signal that the engine is running at a medium or low load condition; The supercharging control valve sends a closing signal, and at the same time sends a working signal to the electromagnetic clutch, and the electromagnetic clutch meshes with the crankshaft transmission to drive the supercharger and the turbocharger to work simultaneously, and the control unit according to the calibrated control The map (MAP) map sends an opening signal to the back pressure valve and exhaust gas recirculation valve installed on the engine exhaust pipe to control the exhaust gas recirculation rate. If the engine is running under a high load condition, the control unit sends an opening signal to the supercharging control valve installed on the engine intake pipeline, and at the same time sends a stop signal to the electromagnetic clutch, and the electromagnetic clutch is separated from the crankshaft drive train , the turbocharger works alone, and at the same time, the control unit sends an opening signal to the back pressure valve and the exhaust gas recirculation valve installed on the engine exhaust pipe according to the calibrated control map (MAP) to control the exhaust gas recirculation valve. cycle rate. The results show that, under the conditions of each emission test, the exhaust gas recirculation rate is 20%-30%, and the exhaust gas is post-treated by the two-stage oxidation reactor, which has the ability to meet the national 4/5 emission. the

Claims (1)

1. method that reduces emission of diesel engine for light vehicle is characterized in that it may further comprise the steps:

(1) control unit read respectively the tach signal that is installed in the sensor on the engine crankshaft, the engine load signal that is installed in the sensor on the gas pedal and according to described tach signal and engine load signal judge motor operate in, the operating mode of low-load or operate in the operating mode of big load;

(2) if during the judged result in the step (1) is, the operating mode of low-load, then described control unit sends shutdown signal to the engine driven supercharging control valve that is installed on the engine charge pipeline, simultaneously send working signal to magnetic clutch, thereby described magnetic clutch and the engagement of bent axle power train drive mechanical supercharger work, this moment, mechanical supercharger was in the combined supercharging working state of connecting with exhaust-driven turbosupercharger, simultaneously described control unit according to the control arteries and veins spectrogram of demarcating to the back pressure valve that is installed on the engine exhaust pipe, and the exhaust gas recirculation valve of exhaust gas recirculation pipeline sends the aperture signal, and described engine driven supercharging control valve links to each other with mechanical supercharger is in parallel;

(3) if the judged result in the step (1) is the operating mode of big load, then described control unit sends opening signal to the engine driven supercharging control valve that is installed on the air inlet pipeline, sends cut-off signal to magnetic clutch simultaneously, and turbosupercharger works independently; Simultaneously described control unit sends the aperture signal according to the control arteries and veins spectrogram of demarcating to being installed in the back pressure valve on the engine exhaust pipe and the exhaust gas recirculation valve of exhaust gas recirculation pipeline.

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