What is an automobile EGR valvePosted by On 2021-04-14

The EGR valve is a mechatronic product installed on a diesel engine to control the amount of exhaust gas recirculation fed back to the intake system. It is usually located on the right side of the intake manifold, close to the throttle body, and connected to it with a short metal pipe leading to the exhaust manifold. Its function is to control the amount of exhaust gas entering the intake manifold so that a certain amount of exhaust gas flows into the intake manifold for recirculation. The EGR valve is a very important and key component in the exhaust gas recirculation device.
There are two types of EGR valves: mechanical and electronic. The picture on the right shows the mechanical appearance.
The EGR valve reduces the temperature of the combustion chamber by guiding the exhaust gas discharged from the combustion of the engine to the intake manifold to participate in the combustion, improving the working efficiency of the engine, improving the combustion environment, and reducing the burden on the engine, effectively reducing the emission of NO compounds, reducing knocking, and extending the components Service life.
The full name is Exhaust Gas Recirculation, or exhaust gas recirculation system, used to reduce the emission of nitrogen oxides (NOX) in exhaust gas. Nitrogen and oxygen only undergo chemical reactions under high temperature and high pressure conditions. The temperature and pressure in the combustion chamber of the engine meet the above conditions, especially during forced acceleration. When the engine is running under load, the EGR valve opens, allowing a small amount of exhaust gas to enter the intake manifold and enter the combustion chamber together with the combustible mixture. When idling, the EGR valve is closed, and almost no exhaust gas is recirculated to the engine. Automobile exhaust gas is a non-combustible gas (excluding fuel and oxidizer) and does not participate in combustion in the combustion chamber. It reduces the combustion temperature and pressure by absorbing part of the heat generated by combustion to reduce the amount of nitrogen oxide generated. The amount of exhaust gas entering the combustion chamber increases as the engine speed and load increase
Exhaust gas recirculation is a method in which part of the exhaust gas is introduced to the fresh air (or mixed gas) inhaled during the operation of the engine and returned to the cylinder for recirculation to participate in combustion. Its function is to reduce NOx emissions. NOx is a gas that is extremely harmful to the human body, and it is mainly generated under high temperature and oxygen-rich conditions. In the engine working process, if part of the exhaust gas is reintroduced into the cylinder in a timely and appropriate amount, because the main component CO2 in the exhaust gas has a relatively large specific heat capacity, the exhaust gas can absorb part of the heat generated by combustion and take it out of the cylinder. A certain dilution effect reduces the maximum temperature and oxygen content of engine combustion, thereby reducing the amount of NOx compounds generated.
However, excessive exhaust gas recirculation will affect the normal operation of the engine, especially when the engine is running at idling speed, low speed and light load, and the engine is running in cold state, and when the engine power is required at full load (throttle opening), the recirculation is Exhaust gas will have a serious impact on the performance of the engine. Therefore, the amount of exhaust gas involved in the recirculation should be automatically adjusted according to the actual working conditions of the engine and changes in working conditions. Practice has proved that, depending on the structure of the engine, the amount of exhaust gas involved in recirculation generally varies between 6% and 13%.
In order to prevent the exhaust gas recirculation amount from having an excessive impact on engine performance, modern electronically controlled engines also adopt a closed-loop control strategy for exhaust gas recirculation, and set an EGR valve position sensor at the exhaust gas recirculation valve (exhaust gas temperature sensor is also used on some models) (Or pressure sensor), closed-loop correction feedback control of the actual exhaust gas recirculation amount.

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