Quote:
Originally Posted by HarryM1BYT
Thanks for that. So if I understand the combustion part of the process correctly, it means a less complete combustion, a cooler combustion and more fuel used to over come the poorer efficiency when the EGR valve opens - is that about right?
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Not neccessarily less complete, but a slower rate cos the oxygen is not in as great an excess, and so a cooler rate. It is still complete combustion though, (no permanent smoke) so efficiency should not be any different.
Remember that the amount of gas recirculated is calculated by the designer, and controlled by the EGR valve system, so that the fuel mixture will probably never get too rich ( for diesel engines ).
Thinking about this further, Diesel engines always run lean, there is no throttle to restrict the intake air. The EGR valve can be regarded as a throttle that restricts the oxygen supply.
Of course all these arguments refer to a steady state, things will be different when the pedal hits the metal suddenly.