What does "horsepower hours per gallon of fuel" me

I don't understand the Nebraska Tractor Test results for the fuel economy test results. What do they mean by when they say they are expressing the results in "horsepower hours per gallon of fuel"? What exactly does this mean?

Thanks

Sounds self explanatory to me. It's a variant on how much fuel to make horsepower for an hour. The lower the amount of fuel/ the higher the hp per hour equals the efficiency. I'dd use it to compare between models. Sort of like mpg in a car.

yOU WILL GET MORE HOURS per gln DRIVING AROUND SIGHTSEEING THAN IF YOU ARE PLOUGHING A PADDOCK.
[view it as being in small print]

It's called "specific fuel consumption". Basically, it's "energy out" divided by "energy in". A horsepower-hour is a unit of energy (energy = work; work = power x time). Although a gallon of fuel is not technically a unit of energy, for a given type of fuel the Btu's of energy per gallon is known.

Another way you'll see specific fuel consumption listed is gallons per horsepower-hour or pounds per horsepower-hour. (Actually these number are the reciprocal of hp-hours/gallon.)

It"s how much work a tractor can perform per gallon of fuel.
Eg. a tractor that burns only 2 gallons of fuel per hour and making 28HP is a crummy machine compared to a 15 gallon per hour tractor making 255HP.
Yet most people will stand there and say the 15 gph tractor is a fuel hog. Isn"t so.

It's a way to compare all tractors with fuel efficiency in mind. Obviously, "miles per gallon" would't work well - especially with PTO work involved.

An old John Deere B, or a Ford 8N will run a four or five foot brush hog more efficiently than some of the newest and highest rated turbo-diesel tractors. It's nice to have the tests so you can compare.

If you look at the complete tests - and NOT the abreviated tests that are often reprinted - they can tell you a lot. Many modern tractors with the highest claimed fuel-efficiency are absolute dogs when used at lower power levels. So . . . if you read the full tests, you can figure what tractor is best suited for the type of work you want to do. For example, and old Ford flathead, gas engine 8N can run a 4 or 5 foot brush hog more efficiently than a new 150 horsepower turbo-diesel Deere tractor. That because most tractors that are very efficient when worked hard, are inefficient when used a low power.

One example - running a 5 foot brush hog that might need 15-25 horsepower, The higher the number, the more fuel efficient. An old Deere B or Ford 8N is almost twice as efficient as a new 160 horse Deere in this situation:

Deere B - 11.7 test rating
Ford 8N - 11.1 test rating
New Deere 7630 turbo-diesel - 6.5 test rating.

1947 John Deere B (two cylinder gas) tested making 25.79 horsepower for two hours and got a rating of 11.79. At 18.7 horse it was 10.9. At 14.8 horsepower it dropped to 9.5. At 12.8 horse it was 9.2, and when worked at only 6.4 horsepower it dropped way down to 6.

2007 John Deere 7630 turbo-diesel. When worked at 161.8 horsepower it is rated at 18.16. When worked at 92 horse it drops to 14.3. When worked at 62 horse it drops to 12.4. When only worked at 31 horsepower it drops way down to 7.6.

Note that an 8N Ford can make 25 horsepower with a rating of 11.l horsepower hours per gallon.

A horsepower-hour is equivalent to 745.7 watt-hours or to use a more familiar measure 0.7457 of a kilowatt-hour. Dividing it by the amount of fuel used to produce it gives you a measure of efficiency.

Put a motor on a dyno so you know it's output, and multiply that by the length of a given run in hours. That's your horsepower-hours for your calculation. Dividing that by the amount of fuel consumed on the same run gives you a measure of efficiency, hp-hrs/gal.

In the electrical analogy, a generating station might gauge the thermo-mechanical efficiency of it various types of standby (peak-hour) generators by comparing the kilowatt-hours produced by a diesel driven generator using gallons of diesel fuel used, or in the case of a gas turbine, cubic feet of gas consumed. There is also a conversion from hp or watt-hours to BTUs, so in essence they are looking for the highest (most efficient) ratio of BTUs in to BTUs out. The BTUs available per unit of either fuel would be known, so they might convert the fuel volume to BTUs to gauge thermo-mechanical efficiency, but in economic terms they might also plug in the cost per BTU of each type of fuel, and decide which generator to spin up first on that basis.

Nebraska was simply developing the same data for the purpose of comparing the efficiency of various tractors.

I was talking 80% to full load ratings. Thinking cultivating 7ft v.s 56ft wide type of idea.
Of course a small tractor operating at near it"s rated HP will burn less fuel than a tractor twice as large operating at 1/2-2/3 of rated HP.
A partly loaded boiler,gas turbine, diesel or other "unthrottled" engine. Just carries extra air through the combustion chamber. This air carrys combustion heat we paid for. Out the stack and wastes it.

If you will look at the Neb. Test, you will find that the most fuel efficent tractor ever tested was a 730 JD Deisel. Way newer tractor are not as efficent is they are pulling hydrulic pumps. Some of these pumps are fairly larger HP users even if on a open center system. The 730 pump was small and if like the one on a 630 could be disengaged. We had a 730D for a short time and I do not remember if it could be disengaged.

Kent

It"s a measure of the engine thermal efficiency. It"s called specific fuel consumption and is defined by measuring the instantaneous horspower being produced and dividing it by the instantaneous fuel flow rate in gallons per hr that is producing that power.
Most engineering work defines it in terms of brake horsepower hour per pound of fuel so you will often see it written as BSFC = brake horsepower-hr/lb. farmers don"t buy fuel by the pound, they buy it by the gallon so it can be expressed in terms of gallons by knowing what the fuel density is.

BSFC, or brake specific fuel consumption is usually stated by manufacturers as lb/bhp/hr or
g/KW-h(grams/kilowatt-hour).
It basically is the amount of fuel the engine will use in 1 Hour, more HP more consumption.
BSFC = Pounds of fuel per hour/BHP
Example: An engine rated at 475HP uses 150.1 Lb. of fuel.
150.1/475=0.316Lb./hp-hr (192g/KW-h).
Guido.

I have a 1951 JD G, rated use 3.9 gallons /hour to make 38 hp and I am inheriting my Dad's 560 Farmall rated use 12.4 hh/g to make 61 hp.
My question is: is it a straight comparison between gallons/ hour and hh/g?
If so, the Farmall will use 3 times as much fuel to make 1.75 times the hp?