What does EGR valve do?

Exhaust gas recirculation is a method of introducing a part of exhaust gas into the inhaled fresh air (or mixed gas) and returning it to the cylinder for recirculation and combustion during engine operation, which is used to reduce the emission of nitrogen oxides. Nitrogen oxides are a kind of gas that is extremely harmful to human body, and are mainly produced under high temperature and oxygen-enriched conditions. When the engine is working, if part of the exhaust gas is introduced into the cylinder in time and in a proper amount, because CO2, the main component in the exhaust gas, has a large specific heat capacity, the exhaust gas can absorb part of the heat generated by combustion and take it out of the cylinder, thus diluting the mixed gas to a certain extent, thereby reducing the maximum temperature and oxygen content of engine combustion, and thus reducing the amount of nitrogen oxide compounds.

However, excessive exhaust gas recirculation will affect the normal operation of the engine, especially at idle speed, low speed and light load, when the engine is running in a cold state, and when the engine power is needed at full load (full throttle), the recycled exhaust gas will have a serious impact on the performance of the engine. Therefore, the amount of exhaust gas involved in recirculation should be automatically adjusted according to the actual working conditions and working conditions of the engine. Practice has proved that it is appropriate to change the amount of exhaust gas involved in recirculation between 6% and 13% according to the different engine structures.

In order to avoid the excessive influence of exhaust gas recirculation on engine performance, modern electronically controlled engines also adopt closed-loop control strategy for exhaust gas recirculation, and install EGR valve position sensor at the exhaust gas recirculation valve (some vehicles also adopt exhaust gas temperature sensor or pressure sensor) to carry out closed-loop correction feedback control for actual exhaust gas recirculation.