Lean-of-Peak, Rich-of-Peak = (ROP and LOP)
Since OEMs are in a never ending quest for emission reduction and gas
mileage, those two goals drive much of the new technology. NOX production
and detonation are both temperature related so lower EGTs are a good thing.
However, lower EGT could result in either increased efficiency (getting the
more work out of the BTUs available) or it could be very inefficient (LOP or
ROP) meaning the AFR is on either side of stoich. Stoich (14.7:1 for
gasoline) results in the peak highest temperature of combustion. Stoich is a
poor environment for both detonation and NOX. To get efficiency, gas
mileage, lower detonation tendency, and lower NOX, you would want to drive
the equation to the highest LOP and still have a smooth running engine.
Traditionally, smooth running with an AFR 15:1 or higher, was difficult to
achieve. However, direct injection, VCT, COP, knock sensing, and EMU spark
control, all come together with a high CR to extract as much useful work as
possible from a smooth running engine in a LOP environment that could not
exist without all of them working together.
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