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Old 12-06-2010, 07:36 PM   #159 (permalink)
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Originally Posted by Old Mechanic View Post
One site I checked was 124k BTU for gas and 139k BTU for diesel, so that's 12% higher BTU content per unit of volume for diesel.

Originally Posted by Old Mechanic View Post
I wonder what the dyno figures would be in difference between gas and diesel engines at the load that would run both at best efficiency.

I think under those close to identical situations the difference is about 34% for typical gas engine and 40% for typical diesel, give or take a coupe percentage points for either.
I am not following what you are trying to identify. To compare the engines, you load them identically and measure the fuel consumption. Gassers are generally let out on the street packing 50% to 100% more power than diesel engines, so perhaps you are thinking at a cruising load the diesel would be operating in a more efficient load range.

You may be right. That would help explain how gassers can close the efficiency gap with hyper-miling techniques.

Originally Posted by Old Mechanic View Post
Adding 12% to 34% would get you to 38% which is why I thought the most significant difference would be due to energy content in the fuel, with the rest due to other factors.
It's a difference for sure, but I don't think you have your baseline efficiencies correct, so I don't think the energy content is as significant as you claim.

Originally Posted by Old Mechanic View Post
Pumping losses are something else I would like to see others opinions as to sources, but it would probably be better to start a different thread on that subject.

I think pumping losses are completely on target for this thread. Obviously gassers have much higher losses when operated at a percentage of full load because of the throttle. I don't know how to quantify that loss though. I'm sure there is good data on factory engines out there though where you can make apples-apples comparisons, say for example equalizing displacement or rated power. And you can equalize the fuel energy content as well, just use B100!
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