Horsepower hours per gallon- help me understand

[DarkBlack]

There is no way you will get 31HP at the PTO with a fuel use of .8 GPH.

I agree
31HP for an hour is 78,877 btu's
0.8 gallons diesel is 109,253 BTU's
That would make a 72% efficiency. Nope-Not in some ones wildest dreams. Even a diesel engine by itself can't achieve that, and that's not counting all the losses of the transmission, alternator etc..

 

[Gary Fowler]

I agree
31HP for an hour is 78,877 btu's
0.8 gallons diesel is 109,253 BTU's
That would make a 72% efficiency. Nope-Not in some ones wildest dreams. Even a diesel engine by itself can't achieve that, and that's not counting all the losses of the transmission, alternator etc..

The problem with recording fuel used /hours ran is that no one can measure the HP being used. Max HP on the engine determined with a dynamometer is recorded when the engine starts to stall. No one can run their tractor at this setting (lugging just before stall) and expect it to last any large amount of hours.

 

[zzvyb6]

Take the reciprocal of the hp-hr/gal numbers (1/over) and figure it as gal per hp-hr. That reduces to gal/hp for 1 hr. Then multiply by the pto hp. Which makes much more sense for comparison purposes, since the 'gallons' number seems to be the one posters are asking for.

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Homework assignment:

Look up the numbers for a few equal hp tractors with 3, 4, 6, and 8 cylinder tractors. Identify which motor configuration delivers the best fuel efficiency.

Just the facts, no opinions....

 

[Jerry/MT]

The problem with recording fuel used /hours ran is that no one can measure the HP being used. Max HP on the engine determined with a dynamometer is recorded when the engine starts to stall. No one can run their tractor at this setting (lugging just before stall) and expect it to last any large amount of hours.

You're correct on the ability of the tractor user to determine engine hp being used. You could calibrate the engine hp vs rpm and fuel flow vs rpm and measure fuel flow and rpm to get back to hp, however. Even this is beyond the typical user.

However, max power on a diesel engine is determined by the apppearance of black smoke (actiually a certain smoke number) in the exhaust-more is fuel being added than can be burned in the cylinder. When you see a hp vs rpm curve for a diesel, that's how it is determined.