Quote:
Originally Posted by diesel_john
"Unfortunately, for us, auto mfrs like to use fuel for it's heat capacitance rather than it's combustible characteristics "
could you explain, i don't understand what heat capacitance is.
(the learning gradient is too steep for me)
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In order to prevent detonation under boost in a turbocharged engine during high load, the computer will sometimes increase the air fuel ratio from the stoichiometric 14.7 to 1 ratio to something closer to 13 or 12 to one. Because liquid fuel has higher latent heat than air, the extra fuel injected into the engine is used to absorb heat from the combustion chamber and prevent detonation. This fuel does not get burned in the combustion chamber (not enough oxygen) so its wasted out the exhaust in the form of extra pollution. One solution to this problem is to maintain the 14.7 AFR even at high load and inject water to prevent detonation instead of fuel.
This is was also common practice in most non turbo fuel injected engine but to a lesser extent until very recently. Manufacturers got away with this practice because EPA emissions test did not include a full load (throttle to the floor) cycle.