PTO GENERATORS

[Soundguy]

nebraska tests have some data on fuel usage at load.. etc.. for anyone that cares to read them...

 

[txhillcountry]

no.. i didn't say that.

i said equal loads will generally use about the same fuel. you may see some loss difference on a larger machine due to some friction and mass differences.. then again you may see differences the other way based on a machine running outside it's power band and being slightly less efficient.. etc.

we can assume in your 'car' example.. that at least one of the rpm ranges you specify are outside of it's power band ... among other things.. etc..

Well, all I can say is that John Deere is betting a lot of money that "economy PTO" is effective.

"See how John-Deere exclusive economy PTO function can save customers fuel, wear, and money"
Savings Plan - YouTube

I agree with you in general terms about load and fuel consumption, but practically speaking, it does work for some PTO-driven implements (fuel savings, that is.)

TX

 

[Soundguy]

i would agree that in situations were you need rpm, and not so much hp.. that you would find a benefit.. if only from decreased wear.

Well, all I can say is that John Deere is betting a lot of money that "economy PTO" is effective.

"See how John-Deere exclusive economy PTO function can save customers fuel, wear, and money"
Savings Plan - YouTube

I agree with you in general terms about load and fuel consumption, but practically speaking, it does work for some PTO-driven implements (fuel savings, that is.)

TX

 

[xring100]

wow...

i guess you aren't thinking about the fact that in most cases.. fuel useage is based upon load.. not just rpm.

if your machine is making 10kw of electricity.. it will make little difference if it is doing it at higher or lower rpm.

you have a fuel efficiency and conversion to electricity cal to do.

fuel usage = load for the most part on a modern engine...

what you said true but when you factor in the engines efficiency shown in the attached brake specific fuel consumption which shows the engines in terms of fuel usage you understand why engine RPM not just load also impact the fuel economy and why economy pto's save fuel
example 1
Part 1 1650 RPM
Looking at these curves lets say you need all 70 hp (about the max power that this engine makes at 1650 rpm) this motor uses about .335 lbs of fuel/(hp hour) that translates to 23.45 lbs of fuel per hour.
Part 2 2600 RPM
now lets say your running the engine at WOT 2600 rpm using the same 70 hp load the engine uses about .375 lbs of fuel/(hp hour) totaling 26.25 lbs of fuel
diesel weights roughly 7 lbs a gallon
For Part 2 you would burn 3.75 gallons per hour for Part 1 you would Burn 3.35 gallons per hour or .5 gallons per hour difference In terms of dollars $2 per hour when diesel is $4 a gallon I realize this is a worst case assessment but its only to illustrate why over time an economy PTO saves Farmers money. If your only talking a few hours your right fuel usage is similar. but over hundreds or thousands of hours big money can be saved.

Running the tractor at slow speed does not mean you actually save fuel example
Tho one that people have the hardest time grasping is the fact that faster rpm can mean less fuel usage in the case where you run your tractor at 1700 rpm versus 1000 rpm you will actually use less fuel at 1700 rpm the engines efficiency comes into play here. People automatically assume that if the tractor will do the job as slower RPM they are saving fuel
Example 2 abbreviated
lets say your doing loader work and only run the tractor at 1200 rpm because you think your saving fuel rather than running the tractor at higher RPMs and your hydraulics are reasonably responsive in this range let say your average 30 hp load over the hour your burning about 1.6 gallons assuming about .36 BSFC and again at 1750 rpm your using about .335 bfsc you burn about 1.43 gallons so you spend about $0.70 per hour more running the tractor slower

 

[fordmantpw]

Just to add in, running at a higher RPM adds more frictional losses since the pistons have to travel a further distance. For instance, for a specified amount of time, running at 2500 RPM, the pistons would have to travel 2/3 further than if the the tractor was running at 1500 RPM, and this will have the additional losses due to friction, oil pumping, water pumping, not to mention 2/3 more combustion cycles and 2/3 more fuel injection events. Taking all of that into account is simple if the tractor is under no load.

However, if the tractor is under load, you have to look at the most efficient RPM for the tractor for the current load, and other factors other users have mentioned. This will vary for different engines, different engine sizes, gas vs. diesel, etc.

This thread is definitely an interesting read!

 

[xring100]

Just to add in, running at a higher RPM adds more frictional losses since the pistons have to travel a further distance. For instance, for a specified amount of time, running at 2500 RPM, the pistons would have to travel 2/3 further than if the the tractor was running at 1500 RPM, and this will have the additional losses due to friction, oil pumping, water pumping, not to mention 2/3 more combustion cycles and 2/3 more fuel injection events. Taking all of that into account is simple if the tractor is under no load.

However, if the tractor is under load, you have to look at the most efficient RPM for the tractor for the current load, and other factors other users have mentioned. This will vary for different engines, different engine sizes, gas vs. diesel, etc.

This thread is definitely an interesting read!

The most efficient point for any given load is in the RPM band that has the lowest Brake specific fuel consumption period, assuming you generate sufficient power at that RPM for the required load. But with a generator your kind of at the mercy of what ever rpm you have to get 60 Hz power. If you have enough horsepower and an Eco PTO mode your good. In the case of the M9540 540 PTO is 2200 rpm if your generator and tractor is only pulling 20hp ~10kw the difference between 2200 rpm and 1650 rpm is only about 0.05 gallons an hour 1 gallon/hr worst case.

To Soundguy's point its not much different at this horsepower level

 

[Soundguy]

not disagreeing with you.. but since pto rpm is a fixed ratio based upon engine speed. I don't think those 2 examples are going to be usefull in compairing to a pto operation for the pto gen we are talking about.

not a single tractor i own has the pto setting at "WOT" thus using 'WOT' as a comparison point is a tad fallacious or at least or at least an obfuscation...

we would need to see the usage at load at (engine)pto speed.. and then usage at that same load at the (engine) Epto speed.

you will obviously have to choose a hp load that is going to be able to be handled at the Epto setting.

since that 1/2 comparison is so close still.. a couple bucks. and we are talking about emergency generator usage. i think that may have to fall into 'minutia'

soundguy

what you said true but when you factor in the engines efficiency shown in the attached brake specific fuel consumption which shows the engines in terms of fuel usage you understand why engine RPM not just load also impact the fuel economy and why economy pto's save fuel
example 1
Part 1 1650 RPM
Looking at these curves lets say you need all 70 hp (about the max power that this engine makes at 1650 rpm) this motor uses about .335 lbs of fuel/(hp hour) that translates to 23.45 lbs of fuel per hour.
Part 2 2600 RPM
now lets say your running the engine at WOT 2600 rpm using the same 70 hp load the engine uses about .375 lbs of fuel/(hp hour) totaling 26.25 lbs of fuel
diesel weights roughly 7 lbs a gallon
For Part 2 you would burn 3.75 gallons per hour for Part 1 you would Burn 3.35 gallons per hour or .5 gallons per hour difference In terms of dollars $2 per hour when diesel is $4 a gallon I realize this is a worst case assessment but its only to illustrate why over time an economy PTO saves Farmers money. If your only talking a few hours your right fuel usage is similar. but over hundreds or thousands of hours big money can be saved.

Running the tractor at slow speed does not mean you actually save fuel example
Tho one that people have the hardest time grasping is the fact that faster rpm can mean less fuel usage in the case where you run your tractor at 1700 rpm versus 1000 rpm you will actually use less fuel at 1700 rpm the engines efficiency comes into play here. People automatically assume that if the tractor will do the job as slower RPM they are saving fuel
Example 2 abbreviated
lets say your doing loader work and only run the tractor at 1200 rpm because you think your saving fuel rather than running the tractor at higher RPMs and your hydraulics are reasonably responsive in this range let say your average 30 hp load over the hour your burning about 1.6 gallons assuming about .36 BSFC and again at 1750 rpm your using about .335 bfsc you burn about 1.43 gallons so you spend about $0.70 per hour more running the tractor slower

View attachment 310247

 

[Soundguy]

yeah,. you have to make sure your target hp neede dis available at the epto before you make the comparison or all bets are off. epto won't do you much good if it doesn't make the hp needed for the load..e tc.

The most efficient point for any given load is in the RPM band that has the lowest Brake specific fuel consumption period, assuming you generate sufficient power at that RPM for the required load. But with a generator your kind of at the mercy of what ever rpm you have to get 60 Hz power. If you have enough horsepower and an Eco PTO mode your good. In the case of the M9540 540 PTO is 2200 rpm if your not generator and tractor is only pulling 20hp ~10kw your the difference between 2200 rpm and 1650 rpm is only about 0.05 gallons an hour 1 gallon/hr worst case.

To Soundguy's point its not much different at this horsepower level

 

[zzvyb6]

I do believe a science project is in order here.

Someone with an eHydro PTO diesel tractor, a PTO generator/alternator, and a very large electric heater or some other continuous use large electric power sink.

I'd connect a clear tube to the fuel tank suction line and mark two locations on it a reasonable distance apart (say a foot). Then I'd hang it vertically, start the machinery, engage the load and fill the sight tube to above the top line. When the fuel level reaches the top line, start a stop watch and record the time it takes to drop to the lower line. I'd choose a clear fuel line who's diameter gives me a fuel rate indication that takes a minute or so to measure. I'd run it back to back with several levels of load (water pump, stove/oven, etc). We'd also need the reading for the alternator spinning with no load at all (residual fuel rate).

Then run your contest. Best/longest time wins. It is not rocket science to run this experiment. The tractor won't run out of fuel so there is no risk of trouble. The load has to be continuous (no air compressors or A/C units unless they stay on for the entire set of measurements.

And that, my fellow tractor lovers, would help understand this issue and probably deserve an award for effort.

Who is up for the task ??

 

[L355SS]

i would agree that in situations were you need rpm, and not so much hp.. that you would find a benefit.. if only from decreased wear.

The 4600 ford (1978) currently has the eco PTO as the only setting. Engine rpm at 1600 to obtain (540 PTO rpm) 220V output from 25Kw generator.
Dennis