Horsepower hours per gallon- help me understand

Diamondpilot · Feb 14, 2014

MHarryE said:
An 8N uses 2.1 gph at 23 PTO HP. A 4320 uses 8 gph at 117 PTO HP. The arithmetic says the JD is about 45% more efficient at full power. Probably why they don't make tractors like the 8N anymore, and also why gasoline engine tractors (other than lawn tractors) are rare as hens teeth.

Yea. My Jinma tractor puts out 31 HP at the PTO. It has a 6 gallon tank and will run for about 8 hours at full PTO power. So about .8 gph out of its 3 cylinder diesel.

Chris

motownbrowne · Feb 14, 2014

MHarryE said:
An 8N uses 2.1 gph at 23 PTO HP. A 4320 uses 8 gph at 117 PTO HP. The arithmetic says the JD is about 45% more efficient at full power. Probably why they don't make tractors like the 8N anymore, and also why gasoline engine tractors (other than lawn tractors) are rare as hens teeth.

I assume those numbers are from Nebraska. Still I have a hard time believing 2.1 gph. It's hard to know (with no position on the throttle) exactly where 540 is, but in most tasks I do with the 8ns, 1 gallon seems closer to the truth. Furthermore, with diesel being 30% more expensive here, I'll stick with my assertion that I'm glad I'm not fueling the 4320.

Jerry/MT · Feb 14, 2014

buickanddeere said:
Usually a diesel , gas turbine or a boiler operate at peak efficiency at or near full output.

I can't speak for boilers, but most IC engines (gas and diesel) have their best BSFC at around at 75% +/- rated speed. Induction and windage losses at higher rpm's limit efficiency. With aircraft gas turbines best TSFC is also around 75% +/- of max rpm.

SPYDERLK · Feb 14, 2014

Diamondpilot said:
Yea. My Jinma tractor puts out 31 HP at the PTO. It has a 6 gallon tank and will run for about 8 hours at full PTO power. So about .8 gph out of its 3 cylinder diesel.

Chris

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

Industrial Toys · Feb 14, 2014

I always knew that our JD 6200 liked fuel. I recently installed a new electric pump and meter on my farm diesel tank, and keep a record now. Looks like I burned thirty something litres to blow a bit of snow down our 1000 foot driveway on a couple of occasions. I knew it was bad on fuel, but that bad? Can that be right? The tractor only has just over a thousand hours. Still cheaper then paying someone I guess!

Jerry/MT · Feb 14, 2014

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

I agree with spyderlk. A BSFC =0.8/31=0.0256 g/hp-hr or 0.172 lb/hp-hr is just not possible for a diesel. How do you know the load on your tractor was 31 hp? just because the shaft was running at rated speed doesn't mean the load was 31 hp.

Per the Nebraska data (JD6420) the nominal minimum BSFC for modern tractor diesels is some where around BSFC ~0.060 gal/hp-hr +/-~ 0.40 lb/hp-hr +/-at rated speed. All these numbers are for pto hp not engine HP. The BSFC will be lower based on engine HP.

At ~ 80% rated speed and max pto hp it was BSFC= 0.059 g/hp-hr+/- = 0.37 lb/hp-hr +/-. The larger engines will generally do a bit better than this but these are good "ball park" installed BSFC numbers for these type of discussions. Thse data illustrate two points; best BSFC doesn't occur at max rated engine speed and max engine power and the modern diesel has a best BSFC of around 0.40 lb/hr-hp= 0.06 gal/hp-hr. It does indicate that max shaft horse power at the pto occurs at lower than rated engine speed also. Since max engine power generally occurs at max rated speed, this imples that gear train losses are becoming very large with increasing engine speed which is somewhat intuitive.

MHarryE · Feb 15, 2014

If you check the Nebraska tractor test results both the 8N and the larger tractor have the best BSFC at maximum power. At 1 gph the 8N is producing 3 horsepower for the last produced. The older ones used more than 1 gph running at high idle no load. But of course the large tractor is going to use more fuel per hour doing the same job as an 8N because it will be way down on the performance curve where most of the power is going to parasitics. Like our smallest tractor, a Kubota L5740, will use less fuel clearing snow than our 160 HP JD7720, but put our 6 x 18 plow behind the Kubota and --- well I guess the Kubota will win there too because the engine will die and it won't use any fuel. A more fair comparison - we have a 2 x 14 plow that the L5740 will handle quite well. My partner and I measured out 2 acres plots in a field and plowed with the JD against the Kubota. Besides taking 4 times longer to plow, the Kubota used more than twice as much fuel for the same amount of work.

Diamondpilot · Feb 15, 2014

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

Well I have 900 plus hours on this tractor in the last 10 years pushing snow, Bush Hogging, ect. It will run about 8 hours before it needs fuel. Tank is 6 gallons.

Now if it's actually using all 31 HP is the question? I do know that on a dyno at my dealer it turned 31 HP though. We tweaked the Injection Pump Timing to tune it in when I took delivery.

Chris

Jerry/MT · Feb 16, 2014

Diamondpilot said:
Well I have 900 plus hours on this tractor in the last 10 years pushing snow, Bush Hogging, ect. It will run about 8 hours before it needs fuel. Tank is 6 gallons.

Now if it's actually using all 31 HP is the question? I do know that on a dyno at my dealer it turned 31 HP though. We tweaked the Injection Pump Timing to tune it in when I took delivery.

Chris

Chris

What load did you have on the pto when you measured the fuel flow. If you measured the fuel flow when it was on the dyno, you'd have an idea what the bsfc of the system through to the pto shaft was. In general, bsfc would be higher than if you measured the gross power at the engine shaft because of the gear train losses.The level you qouted is much lower than the typical tractor levels measures at the Tractor Test Lab and you have a very small engine. Scaling laws say you tractor shoud be worse not better.