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Brake Specific Fuel Consumption (BSFC) and the Energy Contained in Diesel and Gasoline

Here are some thoughts on Brake specific fuel consumption (BSFC) and the energy contained in diesel and gasoline.

A gal of diesel fuel weighs 7lbs and contains about 19,000btu/lb, or 133,000BTU/gal. Divide by 2545 to convert BTU to HP and you get about 52HP/gal.

A gal of gasoline has about 17,000BTU/gal and weighs about 6lbs/gal, or 102,000BTU/gal, divide by 2545 to get about 40hp/gal.

A modern diesel engine will burn between .33-.50lbs/bhp/hr, or yield as much as 21hp/gal, or as little as 14hp/gal.

A modern gasoline engine will burn between .4-.6lbs/bhp/hr, or yield as much as 15 hp/gal, or as little as 10 hp/gal.

At $2.00 a gal for fuel, a single hp cost will vary from $.095 to $.20.

The reason for the variation in BSFC is due to the ratio of parasitic loads to output, and the relative combustive efficiency.

Combustive efficiency is optimized at relatively high loads and temperatures, and with high power output the parasitic loads become a smaller percentage.

Using a typical small passenger car that gets 30mpg at 60mph, the fuel consumed will be 2gph. Using the info above for gasoline, the power required will be between 20-30hp. This includes air resistance, friction, and rolling resistance (drag).

I have calculated that a 3000lb car traveling at 60mph requires about 11 hp to overcome gravity. Therefore, the remaining hp (9-19) is the amount required to overcome drag.

Exalt’s goal is to test and confirm these suppositions.

  • Posted on   03/30/09 at 12:18:34 PM   by Jonny  | 
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Tagged with Brake Specific Fuel Consumption, BSFC, Diesel Energy, Gas Energy, Alternative