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Old 01-16-2012, 01:52 PM   #41 (permalink)
mort
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Quote:
Originally Posted by IamIan View Post

ICE's are fairly low efficiency devices ... it is not uncommon at all for ~70% or more of the fuel's energy content to be wasted going out the radiator and the exhaust.
Hi IamIan,
Yes, Otto cycle engines have thermodynamic efficiencies (at WOT) in the range of 25% to 35% so on average 70% of the heat is lost. However I know a little about this subject and dumping 175% of the shaft power into the cooling system at part throttle is incredible. The worst case design rules allow for 100% of full shaft power to go into the cooling system. At reduced power a considerably small percentage of power goes into cooling. As power is reduced peak temperatures, average temperatures and efficiency all fall and a higher percentage of heat goes out the exhaust. In general, high peak temperature provides higher efficiency, but the cooling system removes heat as if from the average temperature. At 2140 rpm and 36 bhp, the engine is throttled down to about 25% I would expect thermodynamic efficiency to be below 15% A common design rule for automotive cooling systems is the radiator must dump 14% of shaft power at cruise. So I see this engine as needing 12 times the cooling I would have allowed.

Sorry, that is completely off topic.

If the paper is to be believed, the addition of 1.5 lb/hr of hydrogen improved efficiency from 21.95% to 22.78% (bhp/fuel hp)
-m

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