Oil & Fuel Fuel Efficiency

fordpowerstroke · Feb 1, 2006

I was reading that a tractor with a bigger engine could be more fuel efficient than a comparable tractor with a smaller engine. Something about the bigger engine might not be working so hard and therefore might be more fuel efficient compared to an overworked, smaller engine. Here's where it talks about fuel efficiency of compact tractors . Do you think the reasoning here is true? Seems like in terms of automobiles, a smaller & harder working engine will usually get better fuel economy than a bigger engine that doesn't have to work so hard. Maybe it's different with tractors.

slowrev · Feb 1, 2006

Perhaps, but it also depends on what you are doing with the tractor. If you are running PTO implements at PTO speed then I would think in almost all situations the bigger tractor would suck more fuel.
Of course I was assuming that both tractors would use the same implement. You might get better fuel efficiency on the biggwer tractor by using bigger implements and getting more done in less time.

Ben

JoeR · Feb 1, 2006

Interesting question. This is more a work vs time analysis. Where the work and time equates to fuel consumption. If you have a 30HP tractor, you may need 2200 RPM's to pull a disc at 3 mph, whereas, a 50HP tractor may only need 1800 RPM to pull the same disc at 3 mph. Of course, the lower the RPM, the less fuel you are burning. If you properly size your equipment and task, then you should not burn more fuel than a larger tractor. The savings should come in the form of time. A 50HP tractor should be pulling a larger disc than a 30HP, which means the 50HP should do the job quicker but would burn more fuel per hour, but the time savings should reduce overall fuel consumption for the job. Overall, when we start to exceed the rated task for the tractor we end up spending more time and fuel on the job. I can mow 2 acres in 1.5 hours with a 60" deck and a 27HP tractor (Deck is almost too big) or I can do it in 35 minutes with a 72" deck and 50HP tractor. Fuel consumption on the 50HP is about the same as the 27HP for mowing the 2 acres.

What's funny, is I decided to read the link after I started typing, and I find that I am saying the same thing. /forums/images/graemlins/smile.gif Sorry for restating it in a different form.

Joe

JerryG · Feb 1, 2006

There has been a lot of talk about this in the Ag world. If you do a search for "gear up, throttle down" you will find a lot of it. There have even been some universities that have done studies on it.

MadDog · Feb 1, 2006

Isn't it, at least in large part, a question of mechanical efficiency? A given task (like disking or mowing a 1 acre field requires (assuming no "overlap") the same amount of physical work and, if both large and small engines run at the same efficiency, should require the same ultimate amount of energy (fuel) to perform that work.

Of course, there are two catches; first, the efficiencies of large and small enginges may NOT be the same and second, the "work" analysis does not consider that the amount of energy necessary to propel the larger, heavier machine around the field is obviously greater and this may, or may not, be offset by the shorter amount of time that the machine needs in the field to complete the work.

It is because their engines are not running any longer to go the same distance that explains, as I understand it, why smaller cars get better mileage, even though their engines generally run at higher rpm and thus are "working" harder. Propelling a lighter, smaller load (with less wind resistance) over a given distance is less work.

I'd be interested in what any engineers or physicists in the group have to say about this.

fordpowerstroke · Feb 1, 2006

That's some good food for thought. Thanks for replying.

Soundguy · Feb 1, 2006

( Isn't it, at least in large part, a question of mechanical efficiency? A given task (like disking or mowing a 1 acre field requires (assuming no "overlap") the same amount of physical work and, if both large and small engines run at the same efficiency, should require the same ultimate amount of energy (fuel) to perform that work.
)

Here's what i observed. For about 3 ys I cut 10 ac with my NH 1920 (33hp ) and 5' mower. Took me 5-5.5 hours to cut, and about 5g of diesel.

I now cut it with my NH 7610s (90 hp ) and 10' mower. Takes me 2.5-3 hours and used every drop of 5g, if not maybee 5.5 g of fuel.

Net result is I only loose a morning to cutting the pasture, vs pretty much blowing the day with it.

Soundguy

hbaird · Feb 1, 2006

I am sceptical of all generalizations on this subject. Most if not all internal combustion engines have max efficiency at torque peak RPM. When you can, run at torque peak or horsepower peak RPM's for the lowest fuel use. Studies done in the 1930's and later have shown 500CC cylinders were about optimum all round. Larger cylinders have lower surface area to volume ratios, so may lose less heat when running. Tests can be run to prove just about anything. Auto makers are again making engines that are V8's when starting off and going to V4's at cruise to save fuel. I have found best economy at very constant RPM.
Harold

IH3444 · Feb 1, 2006

Lots of considerations with a thread like this, but if I was a farmer, and trying to be fuel efficent. I would select a late model tractor with late model piston, cylinder design tier II emission certified engine, direct injection perfered, gear drive. Bigger engines running lower RPMs, but larger injectors, where do you draw the comparisions except as Soundguy states, run'em side by side. I'd much rather spend another $2 in fuel, and have the afternoon to do other things.

3RRL · Feb 1, 2006

( I'd much rather spend another $2 in fuel, and have the afternoon to do other things.)

How true that is...
There's a lot of value in that for sure. Some that can't be measured by dollars.