Quote:
Originally Posted by Snake2998
That means 1 pound of air, at STP, will be equal to 13.1 cubic feet of air. Now to make 100 Hp the engine will need to process (consume) 131 cubic feet of air per minute. If we have a 600 Hp engine it wll need to consume 131 * 6 or 784 cubic feet of air every minute.
When you consume 784 lbs of air and you are fueling to an AFR of 14.7:1 for Plain Jane gasoline you will need a little over 53 lbs of gasoline per minute. At 6.5 lbs/gallon (in round numbers) that means a fuel delivery demand of a little over 8 gallons per minute! Changes in air density require modificatins to that fuel delivery in real time. This is where the EFI systems shine.
Your calcs are a bit out - using a BSFC 0.50 lbs/hr a 600hp motor will consume:
600 X 0.5 /6.25 = 48 Gals per hr - not 8 Gals per minute.
Otherwise I like your take on things.
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Snake2998’s commentary was spot on when he identified the gasoline consumption as over the top!
As luck would have it, I experienced a high-level spousal interrupt during my original post-authoring phase. When I returned from my mandated honey-do, I assigned the numeric volume of air consumed as if it was the weight of air consumed. The weight was not 784 lbs; the volume was 784 cubic feet, which weighs 59.98 lbs, not 784 lbs. With correct math, the numbers play out as follows;
784 cubic feet of air weighs 60.0 lbs. (784 * 0.0765). A cruising AFR of 14.7:1 would require 4.1 lbs of gas to meet stoichiometry. (I also missed a digit in my gasoline weight representation. Regular Pump gas is reported as 6.25 lbs per gallon by the department of energy and Snake2998
— it was a tough day!). A weight per gallon of 6.25 lbs would equate to 0.66 gallons of gasoline per minute (4.1/6.25), not the 8 gallons per minute I originally represented.
These numbers bring the BSFC to my 0.41 value above. [(Gals/hr)*(Gas Den)/HP]. The 0.41 value assumes, among other things, complete combustion and minimal energy spent to operate the actual engine mechanism. When you factor in combustion efficiency, volumetric, and mechanical efficiencies (or lack thereof for all), a 0.5 BSFC is not an unreasonable expectation. Most significantly, Snake2998’s intuition and quick analysis was spot on! — Thanks for the heads up and clear thinking Snake.
P.S. A similar tip of the hat and thanks should also go to Tony for his early detection of my whoops