Quote:
Originally Posted by christofoo
Right. (Next we have to back off a little since there is now extra work available, resulting in higher FE for a given crankshaft power.)
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Exactly. "Backing off," here, means that we require less fuel than before.
We need only a set amount of available work to push the vehicle forward at a given constant speed. If we decrease the amount of pumping work while keeping the amount of produced work constant (because we're keeping the amount of fuel per cycle constant), we increase the amount of available work, and ultimately go faster than we did before. Not exactly what we aimed for.
So, we decrease the amount of fuel being combusted per cylinder by an amount that will give us the same amount of available work as before.
By lowering intake manifold, we lower the amount of pumping work being consumed, and we lower the amount of fuel being consumed as well, to propel a vehicle forward at a constant speed. This is considered "lean burn".
Agreed?