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To: Slagle who wrote (64000)	5/20/2005 11:20:57 AM
From: energyplay	Read Replies (2) \| Respond to of 74559

That's the right figure for thermodynamic efficency for a given compression and combustion temperature. Off the top of my head, most gasoline engines get 18-23 % conversion of the energy from gasoline, and diesels 21 to maybe 26 % - This based on the energy content of the fuel. That is to the drive shaft, not the wheels, and at optimum operating speed and load. I believe the 59% number is based on the running compression and effective combustion temperature. That number then will tell you how well the engine is runnng mechanically. Increase the compression ratio, allow higher cylinder temps with ceramics, and we get more area in the thermodynamic loop. A small increase in energy recovery of the energy in gasoline say 2%, will mean a nice increase in gas mileage. One of the nasty issues is higher compustion temps mean a lot more NOx emissions. ************** This is one reason for the interest in 'fuel cells' - possible to get about 85-90 % of the energy content of fuel as electricty. That's 3 to 3.5 times an IC engine. Notice also the proliferation of not just 4 speed automatics, but 5 and 6 speed automatics, and much of this on cars with >200 hp. More speeds optimizes mileage. Also provides a selling point.