OK, let's try it this way. The AIR fuel ratio may remain the same, but the oxygen content changes. If 14.7 parts air is atmosphere (no EGR), then that 14.7 has a 21% oxygen content. Now if say 13.7 parts is atmosphere (21% O2) and 1 part is EGR (maybe 1% O2) t... Login to read more.

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