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How they work
The achievement of cleaner vehicle exhaust gas owes much to the quality and efficiency of the Exhaust Gas Recirculation (EGR) Valve. The role of the EGR Valve is to mix the engine’s exhaust gas with the intake air as appropriate for the driving conditions, reducing the concentration of oxygen in the intake air and slowing the combustion speed. As the result of reduced oxygen density during air intake, combustion temperature decreases and lower levels of harmful nitrogen oxide (NOx) are generated.
A small passageway exists between the intake and exhaust manifolds. This is where the Exhaust Gas Recirculation (EGR) Valve is located, where it adjusts the amount of recirculated exhaust gas back into the intake manifold.
When the engine is idling, the EGR Valve is closed and there is no EGR flow into the intake manifold. The EGR Valve remains closed until the engine is warm and operating under load. As the load and combustion temperature start to increase, the EGR Valve is opened and begins to send exhaust gas back into the intake
Due to the technological advances achieved in EGR control and catalyst technology, cleaner exhaust has been achieved even under lean-burn conditions.