The basic EGR system described above is called high pressure EGR. Some EGR circuits have EGR actuator which is adjusted directly by electrical motor (as represented in the engine picture below).Ģ- EGR cooler: reduces the exhaust gas temperature before introducing it to the combustion room.ģ- Flowmeter: the flowmeter calculates the airflow before and after actuating the EGR valve, and sends it to the control unit which calculates the quantity of air reduced after opening the EGR valve and concludes the exhaust gas quantity recirculated.Ĥ- Bypass cooler: allow the recirculated exhaust gas to pass by the EGR cooler or to escape it in case when the engine needs to be heated quickly. It is adjusted by vacuum through a valve.
The EGR system reduces the combustion temperature by two ways, firstly by reducing the combustion speed and secondly based on its high specific heat compared to air, the exhaust gas absorbs more heat in order to raise its temperature which makes the combustion room cooler.ġ- EGR actuator: It controls the recirculated exhaust gas ratio. In order to make the EGR system more efficient the recirculated exhaust gas has to cool down before being introduced by the inlet manifold to the combustion room.
As the exhaust gas temperature is around 800☌ the EGR system re-introduces a portion in order to reduce both the oxygen ratio and the combustion room temperature. NOx appears when the engine runs with excess air at temperatures above 1,540 ☌. So we should reduce the temperature and/or the air ratio in the combustion room. The second solution is to prevent the production of NOx by avoiding the conditions which favor NOx emissions. We could do this using Adblue treatment inside SCR (Selective Catalytic Reduction)(This system will be treated in a separate article dedicated for exhaust gas treatment systems). We have two solutions in order to reduce NOx emissions įirstly, we let the engine run in its favored conditions (which are air excess in the case of the diesel engine) so the engine produces more NOx, then we treat the exhaust gas before the exhaust outlet in order to transform NOx to clean gas.
That’s one reason which explains why diesel engines produce more NOx than gasoline engines as diesel engines run mostly with excess air. The conditions which favor the creation of NOx in the engine combustion are excess air and high temperature. The NOx emissions are a result of the engine combustion of diesel or gasoline with air in certain circumstances. In order to know how EGR reduces NOx emissions we should first know how NOx are produced. Exhaust gas recirculation system (EGR) is an anti-pollution system which allows a portion of exhaust gas to be re-introduced into the engine in order to reduce the nitrogen oxide (NOx) emissions.
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