EGR valve

EGR stands for exhaust gas recirculation. It was one of the first methods deployed to fight high nox values. The valve allows a controlled amount of exhaust to be sent back into the intake of the engine. The exhaust has a high content of carbon dioxide and inhibits the peak combustion pressure thus reducing nox. By using this method car manufacturers are allowed to use higher compression ratios. The recirculation occurs in the lower to mid rpm range. The recirculation stops the enging from knocking (detonating) at part throttle, high load conditions. The egr isn’t used or very little at idle. The combustion pressures are not very high due to low engine speed. Also at a little less than full throttle the egr disengages. By disengaging it allows the combustion pressures to raise and make more power. The engine will not detonate at full throttle, unlike part throttle conditions the fuel ratio will be very rich at or close to full throttle to make power.