Hi drmiller100,
So traveling back in time...
Quote:
Originally Posted by drmiller100
Lets say we inject enough "steam" into the intake stream to eliminate vacuum pumping losses, which I think we all agree are measurable and significant????
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OK, for some numbers, imagine a 2.5 liter Otto cycle at 1500 rpm cruise, the air consumed is about 625 l/m and the volume swept by the pistons is 1875 l/m. To eliminate pumping across the throttle requires 1250 l/m of steam. The saturated steam table says that at 100 C. we can just get to 1.7 l/g. That gives us 735 g/m. The mass of air, 625 l/m is about 590 g/m. The fuel consumption is about 40 g/m. Without testing I can tell that adding 18 times more water than fuel will prevent ignition. If you deliver only as much water as fuel ignition will be difficult, and at that point you only reduce pumping by about 5% Water injection systems used to cool high boost engines often start misfiring at about 20% of fuel flow.
Anybody with a big water tank can try it, but I'm not hopeful that reducing pumping is achievable.
Also on this:
Quote:
Originally Posted by drmiller100
Lower absolute instantaneous temperatures means less losses to the cylinder head/piston.
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Lower peak temperature reduces thermodynamic efficiency faster than it reduces heat loses through the cylinder walls. Higher compression ratios are more efficient, even though heat through the cylinder increases.
-mort