Since the national mandatory implementation of diesel vehicle pollution control 4G remote emission management vehicle terminal H6 (remote OBD) GB-17691 monitoring, Shenzhen Su Rui has collected the relevant parameters of diesel vehicles through the remote emission management terminal according to the requirements of the national standard and the characteristics of diesel engine oxygen-rich combustion , In accordance with the inspection and maintenance system of in-use vehicles, effectively control the emissions of in-use vehicles.
The emissions of CO and HC in diesel engines are relatively low, and the emissions of CO and HC are relatively easy to be controlled by the system matching method, so it is also easier to meet the emission requirements. The emission of NOx and particulate matter must be collected by certain measures to be effectively controlled. There are two main ideas for the emission control of nitrogen oxides in diesel vehicles. One is to suppress premixed combustion to reduce nitrogen oxides, and the other is to promote diffuse combustion To reduce particles.
1. Delay the fuel injection advance angle
Similar to the gasoline engine, the delay of the fuel injection advance angle on the diesel vehicle power system can effectively suppress the emission of nitrogen oxides, and the method is simple and easy. With the delay of the fuel injection advance angle, nitrogen oxides are significantly reduced, but at the same time the fuel consumption rate and soot emissions deteriorate.
There are two main reasons for the delay in the injection time of the diesel engine to reduce the nitrogen oxide emissions: one is to prevent the combustion process from avoiding top dead center, the combustion isovolume decreases, and the temperature decreases; second, the closer to the top injection, the cylinder The higher the temperature of the internal air, the fuel will quickly evaporate and mix and ignite as soon as it is injected into the cylinder, and the lag time after ignition can be shortened. The heat release rate at the initial stage of combustion is reduced, resulting in a decrease in combustion temperature.
It should be noted that the effect of delaying the fuel injection advance angle on reducing nitrogen oxides is limited. Too much delay will often sacrifice fuel economy and particulate emission characteristics, and there is a typical replacement position relationship. For this reason, delay fuel injection advance The angle is best used in conjunction with other measures to accelerate combustion, such as high-pressure injection or enhanced gas movement in the cylinder, hydrogen and oxygen content, etc., to prevent other performance deterioration.
2. Exhaust gas recirculation (EGR)
As mentioned earlier, exhaust gas recirculation is a practical measure to reduce nitrogen oxide emissions from gasoline engines. The role of diesel engine exhaust gas recirculation is the same as that of gasoline engines. The main purpose is also to reduce the nitrogen oxides by reducing the maximum combustion temperature. At present, the exhaust gas recirculation system has been basically covered, except for a few backward old engines and diesel engines. However, with the nationwide enforcement of diesel vehicle pollution control 4G remote emission management vehicle terminal H6 (remote OBD) GB-17691, most of these vehicles are basically away from exhaust gas recirculation, and it is easier to scrap directly.
Because the oxygen content in the exhaust of diesel engines is much higher than that of gasoline engines, and the concentration of carbon dioxide is much smaller, because a large amount of exhaust gas recirculation must be used to effectively reduce nitrogen oxides, the general gasoline engine exhaust gas recirculation rate does not exceed 20% Return flow / (exhaust gas return flow + intake volume) * 100%), but diesel engines (mostly direct injection) are 25% -40%, some even exceed.
60-70% of nitrogen oxides are produced under high load. In this case, proper exhaust gas recirculation is very effective in reducing ammonia oxides. If the exhaust gas recirculation rate is too high, the combustion speed of diesel engine oil becomes slower, the combustion stability becomes worse, HC and fuel consumption increase, and the power decreases. Generally, a cooling recirculation system is used to reduce the intake air temperature, which is more conducive to reducing the emission of nitrogen oxides. When the exhaust gas recirculation rate is lower than 30%, the cooled exhaust gas recirculation recharged diesel engine is more effective in reducing nitrogen oxide emissions than the diesel engine without cooling. In order to achieve the minimum nitrogen oxide emissions, the exhaust gas recirculation system must provide the flow rate as much as possible to allow the maximum combustion unevenness between the cylinders and the error caused by the transient response.
3. Cooling technology in supercharging
When supercharging, it is an effective measure to improve the intake charge of the engine. The most commonly used supercharging method is exhaust gas turbocharging. Supercharging can greatly increase the density of the intake air, can increase the power of the diesel engine by 30% -100%, and can also reduce the quality of the unit power engine and reduce the fuel consumption efficiency. The process does positive work, so fuel economy is better than non-supercharged diesel engines. It is precisely because of the large air excess coefficient of the diesel engine that the generation of soot and particles is easily suppressed, and CO and HC emissions will be further reduced.
However, the inlet temperature after supercharging will often rise to 150 degrees, resulting in an increase in the temperature at the end of compression, which will increase the combustion temperature. At this time, the oxygen-rich combustion may cause the nitrogen oxide emissions to increase, so general drivers It will not drive violently. In addition, turbocharger and cylinder air cooling are used to reduce the intake air temperature and control the deterioration of nitrogen oxides.
4. Optimization of fuel injection system
The optimization of the fuel injection system is to optimize the fuel injection parameters. These parameters include fuel injection timing, injection pressure, fuel injection speed and nozzle hole structure. Increasing the injection pressure, reducing the diameter of the injection holes, increasing the number of holes, and the high subdivision of fuel injection can further improve the atomization of fuel injection in the combustion chamber, further refine the fuel spray particles, increase the contact surface area of fuel and air and shorten the mixing time , Is very helpful to improve combustion and reduce particulate emissions.
The high pressure brought by the turbine can use a large fuel pump to increase the injection rate, and cooperate with the method of reducing the nozzle hole diameter to effectively reduce the ignition lag period and reduce the emission of particulate matter and nitrogen oxides. At present, in the field of refitting, the improvement of oxygen and hydrogen in some stock cars and the blending of some petrol catalysts have certain effects.
The main catalysts of automobiles are oxidizing catalysts and three-way catalyst converters. According to statistics, the catalyst carriers for vehicles in the world mainly include ceramic honeycomb carriers, and some use metal carriers. The ceramic honeycomb carrier has small thermal expansion coefficient, compact structure, small pressure loss, heating block, low back pressure and other hot spots, and the design is not limited by the shape and installation location. The advantages of the metal carrier are fast heating, small resistance, small heat capacity, and fast thermal conductivity. However, the cost is high. At present, the metal carrier is mainly used as a pre-catalyst to improve the cold start performance of the catalytic converter.
Many vehicles already have a multi-injection system, the ECU control system is relatively complex, and the cost is high, and it is not widely used.
5. Non-exhaust pollutant control technology
Non-exhaust pollutants refer to harmful pollutants discharged into the atmosphere by other means than the exhaust pipe, mainly referring to HC compound emissions generated by crankcase blow-by gas and fuel evaporation.
Of the total amount of HC compounds emitted by automobiles into the atmosphere, the blow-by gas from the crankcase accounts for about 20% -25%. When the gasoline engine is running, the high-pressure mixed gas and burned gas in the combustion chamber will more or less leak into the crankcase through the gap between the piston group and the cylinder.
To prevent the crankcase pressure is too high, early gasoline engine generally through the oil port so oiling the crankcase to the atmosphere and a "breathe", which directly crankcase HC compound into the atmosphere. The usual practice is to install a forced ventilation device, rely on the vacuum of the intake manifold to suck the gas in the crankcase into the intake manifold, and re-enter the cylinder to burn it.
Fuel evaporation also emits HC compounds, so if you do not run long distances, it is not recommended that the owner fill the fuel too full. There are two parts here, the fuel tank system also has fuel vapor. The mailbox and fuel system pipe joints are composed of activated carbon tank, control solenoid valve, steam (gas) separation valve and corresponding steam pipeline and vacuum hose. The steam separation valve is installed on the top of the oil tank, and the gasoline vapor in the oil tank enters the steam recovery tank from the valve outlet through the pipeline. The function of the valve is to prevent the fuel in the fuel tank from flowing out of the steam pipeline when the car rolls over. The recovery tank is filled with activated carbon particles, which can adsorb gasoline molecules in gasoline vapor. The other outlet on the recovery tank communicates with the engine intake manifold via a vacuum hose. There is a solenoid valve in the middle of the hose to control the connection and disconnection of the pipeline. The valve is just as simple as you want.
The amount of recovered fuel vapor entering the intake manifold must be controlled to prevent damage to the normal mixture. This control process is implemented by the ECU by controlling the opening and closing of the solenoid valve according to the operating parameters such as the engine's water temperature, speed, throttle opening, etc. When the engine is stopped or idling, the ECU closes the solenoid valve, and the fuel vapor escaping from the fuel tank is absorbed by the activated carbon in the recovery tank. When the engine runs at medium and high speeds, the ECU opens the solenoid valve, and the gasoline vapor stored in the vapor recovery tank passes through the vacuum hose and is drawn into the engine.
At this time, because the intake air volume of the engine is large, a small amount of fuel vapor will not affect the mixture.
The national mandatory implementation of diesel vehicle pollution control 4G remote emission management vehicle terminal H6 (remote OBD) GB-17691 monitoring puts forward higher requirements for practitioners, not only to understand the car, but also to understand car electronics, network, data, collection, calculation , Analysis, and need to know what data is used, this is the most test place for people or teams.
For car manufacturers, to ensure that vehicles can meet emission standards in the design stage before mass production, manufacturers that exceed the emission standards should be strictly monitored through mandatory standards such as "National VI" and corresponding recycling systems. Chinese cars (non-new energy vehicles) have also been sold worldwide.
