Horsepower hours per gallon- help me understand

[Kaliburz]

I tried looking it up via Google and such, but I still don't understand.... well, I don't understand how it relate to find some information I want to find/calculate. I understand that the higher the number in Horsepower hours per gallon, the more fuel efficient the tractor is.

What I'm trying to figure out is, how many gallons of fuel (be it diesel or gas) a tractor burns per hour (and eventually how much it costs to run per hour). Yes, I understand that it can vary due to engine load and type of work being done. But all I come across is this "Horsepower hours per gallon" rating.

I found this site that lists some tractors I want info on:
Diesel Tractor Fuel Economies

But as I said, I'm trying to convert that info into gal/hr fuel used. Is it as simple as dividing the HP rating (PTO, draw or engine) by the Horsepower hours per gallon?

Example: JD 2030 is 60HP PTO w/ a 15.28 Horsepower hours per gallon rating.
That means it would use 3.9 gal/hr when at full pto work.

And a Ford 4000 45HP w/ a 13.9 Horsepower hours per gallon would use 3.2 gal/hr

But that is at what, full load? So just puttering at the field at medium RPM disking or such, would produce better? So at 1/2 or 2/3 load, it will be the same equivalent value?

 

[billbill1]

I am not sure I can explain it but I can tell you how it works for me. I have a 25 hp tractor and operating it at PTO rpm (2300 rpm), it will use about 3 quarts of diesel per hour. Any less rpm and the usage goes down.

 

[joerocker]

I have a 20hp and it uses 1/2 gallon (2 quarts) an hour.

I think it's all going to depend on each individual motor what kind of hourly fuel usage you get.

 

[KICK]

what you are trying to answer is impossible unless you can come up with specifics and eliminate the variables, of which there are many.

 

[SPYDERLK]

Example: JD 2030 is 60HP PTO w/ a 15.28 Horsepower hours per gallon rating.
That means it would use 3.9 gal/hr when at full pto work.

And a Ford 4000 45HP w/ a 13.9 Horsepower hours per gallon would use 3.2 gal/hr

But that is at what, full load? So just puttering at the field at medium RPM disking or such, would produce better? So at 1/2 or 2/3 load, it will be the same equivalent value?

As you are deducing, it will depend on how much work you are doing on an average basis. It will be hard to know this without instrumentation for the most part. A lot of 'work' involves just moving around at wildly varying but average low load conditions. Up to its designed limit the engine only uses whatever fuel it needs to produce the required HP output instant by instant. The easiest way I know to gauge your full load use is to pull a disc harrow in the highest gear your tractor is capable of barely holding its rated HP RPM. This GPH figure will be several times what you normally use doing chores. Keep in mind that there is never a no load condition. Just sitting at hi idle on a 70 HP tractor will use at least a half gallon an hour.
larry

 

[Robert_in_NY]

I wish I could help you but I have never been able to fully understand this either. I know my 7710-II can use 40 gallons of fuel in what seems like no time during a spring day if I am working it hard during tillage. Never have paid attention to actual gallons per hour as it didn't seem like it mattered.

 

[Farmwithjunk]

HP/Hr per gallon ratings, as determined by University of Nebraska testing, is arrived at by an average over a 10 hour test period @ 75% of maximum tested drawbar pull. Test's were run on a 1/2 mile track, concrete surface to keep results consistant from test to test. Former Univ. of Nebraska Chief Engineer, Lester Larson, created a "rolling dynamometer" to apply load. First tests on the concrete track were in 1956. The track was 2 long straight-a-ways with 2 sharp 180 degree turns. (It is shaped like a paperclip)

The John Deere 720 diesel held the economy record from 1956 until 1965 when the Massey Ferguson 150 diesel (see my avatar!) took away that record and held it for several years.

Univ. of Nebraska test criteria is still the accepted standard of the American Society of Agricultural Engineers. (ASAE)

 

[Racer71]

Let me take a stab at this.

Horsepower is a measure of work being done. A 50hp tractor can do twice the work as a 25 hp tractor in the same amount of time. This is where the horsepower-hour comes in.

The 50hp tractor can burn twice the fuel in 1 hour as the 25hp tractor and they will be equally efficient since twice the "work" is done.

Your math above is correct. The JD 2030 will burn more fuel per hour than the Ford 4000. But, since the JD is 60hp verses the Ford's 45hp the JD has done more "work" in that same hour.

Over time the JD 15.28 hp-hr/gal will use less fuel than the Ford 13.9 hp-hr/gal.

All of this is at full load. The dealer should be able to provide a graph showing hp-hr/gal at different rpm. Fuel efficiency varies with rpm.

I hope this helps.

 

[Robert_in_NY]

That makes a lot of sense. Thanks for helping clear it up for me. Hopefully it helps Kaliburz also.

 

[Kaliburz]

Thanks for the info folks.



The main reason I want to know, is, I'm trying to fig. out 'theoretically' how much diesel my JD tractors burn during grape harvest. Granted, all they are doing is moving 'slow' w/ a grape tub while being loaded. The only 'work' is when it gets muddy or when they're 'rev-ed' up to dump. Most of the night, they are about 1100-1200rpm in what ever gear that keeps up w/ the harvester (usually 3rd-5th gear).

(I've guessed at it.... both tractors and harvester run about 1.5 gal per hour. The JD's have a 19.5gal tank, and we fill every two days- 3/4 empty. They run 7-8 hours a night while the harvester runs 2 hours longer- pre and post cleaning. It has a 15gal tank- it gets filled every day.)

I understand that fuel use varies w/ all kinds of variables. But where do I find that information on the web. I know these tractors have been tested up the ying and yang. Does some organization publish this stuff online (w/out a membership).