Good post -- thanks. I had a couple of observations.
Jones Beene wrote: > > A typical IC engine requires a compression ratio of 10-1 to get up > to 85% complete combustion of hydrocarbons (that's about the max, so > there is usually 15% wasted off the top because of the strong > molecular bonding of hydrocarbons) But aren't modern engines, which happily gobble 87 octane fuel, down in the ballpark of 9:1 rather than 10:1? That presumably means they're burning _less_ than 85% of the fuel, yes? Once upon a time I had a car with a compression ratio up over 10 (long since forgotten the exact number) and it knocked like an SOB on anything less than about 95 octane. But it also displaced somewhere between 7.5 and 8 liters and would have gotten sick had I fed it a lead-free diet ... truly it was a child of a different era. > It's not that grim in practice because as the piston goes down and > pressure drops, more and more of the formerly wasted heat can be > returned. But because of these insane requirements, we have been > misled into thinking that high compression is efficient... But it IS "efficient"; a high compression engine can be made very "efficient" indeed. But the "efficiency" it maximizes is the power to weight ratio, not the power to gallons-per-hour ratio!
