Quote:
Originally Posted by ttoyoda
In that video, the engine runs cooler due to very lean mixures or late timing. That is not due to the hydrogen, the use of hydrogen just allows that to be done. They seem to be saying that if you time the engine for later firing, the hot gas stays in contact with the engine walls for less time, thus less heat is transfered to the body of the engine, thus efficiency rises as less heat is wasted heating up parts of the engine.
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Well, I don't have time to waste watching the whole series, and the later timing theory wasn't discussed in that one video above. He did mention exactly what I said (and linked to) about thermodynamic efficiency.
Quote:
Originally Posted by ttoyoda
Also, for this to really be optimized, an engine would get rid of the oxygen sensor and the throttle body to reduce pumping loss and allow really lean mixtures. In an unmodified engine I think the only gain would be from late timing.
The improvements that are happening here are because parasitic losses of the engine are being reduced. I don't think the theoretical engine cycle is being changed.
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Flow obstructions are not the same thing as pumping losses -- oxygen sensors don't cause pumping losses.
In an unmodified engine, later timing would cause
worse performance overall, causing less useful energy to be extracted -- the temperature of the engine might go down, but the temperature of the exhaust would be higher, so the efficiency would be worse. Timing is always BTDC because flame front travel is not instantaneous; you get the maximum energy extraction if the combustion pressure is not "chasing" the piston down, as would happen with late timing.