turning down injector pump?

Anonymous-0 · Feb 20, 2009

I use a larger tractor to run one bale of hay down the road. Can I turn down the injection pump to get better millage for this light load? would the RPM and road speed remain the same? I understand there is a rack travel adjustment and "fuel screw" adjustment. which does what?

Bob · Feb 20, 2009

There's NO NEED to turn down the pump. So long as you are using it for light work, the rack will never get near the "smoke screw" anyhow, so turning down a limit it never reaches anyway will have no effect on fuel economy.

Or, put another way, the "rack setting" is the maximum fuel rate permitted at FULL LOAD, it has NO EFFECT at light loads.

Tramway Guy · Feb 20, 2009

And to add to what Bob said, that is exactly why diesels are so much more efficient at light loads....they take in a full charge of air and only meter enough fuel to maintain the RPM's they are set for. So the air/fuel ratio varies as needed. But a gasoline engine has to have a critical mixture of gasoline to keep running, the total mixture is doled out via the throttle plate. So the air/fuel ratio is more constant, only the volume of this mixture changes. Maximum efficiency is achieved at or near full load.

buickanddeere · Feb 20, 2009

Yes and no.
The diesel engine isn't pumping against a throttle plate at part throttle unlike a part load gasser. Gains there.
However a diesel, gas turbine, combustion boiler, wood stove etc. They all loose/waste combustion heat up the stack. If more air is entering the combustion chamber than what is required for complete combustion.
The extra air just gets heated but doesn't take part in the combustion process.Then carries the heat out of the stack. Some stationary gas turbines actually restrict the airflow into the engine at part load.
That's why when looking at the Nebraska tractor tests. Diesel fuel efficiency at loads under 75% ranges from fair to poor at 25%.
As a "broad, general rule of thumb" A diesel makes the most power per gallon of fuel when loaded down to the point of seeing "a little exhaust smoke". The air-fuel ratio will be down at about 15-16 to 1 with about 1% oxygen going up the stack of the 21% coming in.
This is one of the reasons a turbo diesel enjoys higher efficiency. At part loads the turbo is just rolling without pressurizing the combustion chamber with un-needed air.

NEsota · Feb 20, 2009

Tramway Guy: Your explanation makes sense to me when dealing with carbureted and maybe throttle body gas fuel injected engines. Is this true at all or to the same degree with port fuel injection?

Jerry/MT · Feb 20, 2009

"Turning down the pump" would only limit your maximum power. For running down the road, you are running at part load so it would have no effect.

Brian Jasper co. Ia · Feb 20, 2009

The biggest reason a diesel is more fuel efficient than a gas is volumetric efficiency. The higher compression ratio results in a much smaller combustion chamber. The smaller chamber evacuates more of the exhaust out. The next is fuel injection directly to the combustion chamber. Lastly is diesel fuel has more BTU's in it than gasoline.

buickddeere · Feb 21, 2009

I would debate volumetric efficiency as the reason diesels are more efficient.
Turbo diesels and new diesels with egr leave more unburned exhaust in the combustion chamber.
We are talking part throttle economy here. You are talking economy at 85+% load.
Of course at full load the expansion ratio. It is the expansion ratio, not the compression ratio that contributes to higher efficiency b.t.w.
And yes the higher btu's per lb of fuel and the unrestricted intake tract.
But again...........we are talking part load efficiency here.
Take a look at any 100HP diesel on the Nebraska tests and load it to only 25-50HP. The fuel efficiency will be worse than a decent 50HP gasser in the same application.

turning down injector pump?

Anonymous-0

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Bob

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Tramway Guy

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buickanddeere

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NEsota

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Jerry/MT

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Brian Jasper co. Ia

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buickddeere

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