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The EGR system routes many of the exhaust gases (6 ? 10%) through the EGR valve, last on the Intake System, and in the end in the combustion chamber. The exhaust gases are inert i.e. they don't burn within the combustion chamber; also, the exhaust gases use up a number of the space which could preferably be taken with the intake air. This decreases the volume of intake air available for the combustion process during each Power Stroke; which experts claim decreases the peak combustion temperatures. This leads to lower NOx emissions.