Reducing Diesel Engine Output 3

[yose12]

I have a task that only needs around half of my single-cylinder diesel engine's rated capacity.

The question is, what is the simplest way to run my engine at partial load without sacrificing efficiency? The obvious ones are reducing displacement through a sleeve, or possibly an EFI conversion. But that takes a lot of work.

I have read somewhere about insulating the whole cylinder block to minimize heat loss when running the engine at low rpm. Any thoughts on this?

btw, for the sake of discussion let's not consider getting a smaller engine an option. Im already using a 2.5kw diesel engine. I don't know if there's a smaller one available in the market today.


TIA.

 

[patprimmer]

That depends on how it is cooled.

Not much point in insulating the outside of a water jacket


Regards
Pat
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[yose12]

It's only air cooled, sir patprimmer. The outside of the cylinder walls are finned.

 

[patprimmer]

Does it have a fan and a thermostat


Regards
Pat
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[moon161]

Diesels run well at part load because they typically don't work sucking air in past a throttle plate, and typically run lean to begin with.

How bad is the fuel use at the intended load?

 

[BrianPetersen]

I don't think there's anything worth doing, beyond simply letting it run at whatever part-load setting that it wants to run at.

Trimming the cooling fan so that it is pumping no more air than necessary to keep the cylinder head at an acceptable temperature, to reduce fan losses, might be worth doing.

 

[CCycle]

Diesel engines have the ability to retain their efficiency at low loading. As already mentioned, about the only thing you can do is reduce spurious losses. If the generator is belted you can change pulleys to reduce engine RPM.
Or use an inverter generator. They allow engine RPM to be independent of line frequency. They are set up to run the engine just fast enough to develop the power needed. Inverter generators are becoming quite popular since they reduce noise and significantly reduce fuel consumption at low load.

 

[Tmoose]

"The results indicate that the lowest BSFC of the engine is found when the engine runs around 1 kW charging load when the engine speed ranged between 1900 rpm-2700 rpm. "

http://ieeexplore.ieee.org/Xplore/l...033107.pdf?arnumber=1033107&authDecision=-203

This curve for a generic diesel suggests at some rpm the BSFC is less than 10% worse at half load.

http://upload.wikimedia.org/wikiped...600px-Brake_specific_fuel_consumption.svg.png

 

[gruntguru]

This curve for a generic diesel suggests at some rpm the BSFC is less than 10% worse at half load."

Yes less than 10% worse at half load same rpm.

Best consumption at HALF POWER is 216 at just under 1700 rpm - less than 5% worse than peak BSFC.

Engineering is the art of creating things you need, from things you can get.

 

[yose12]

Thank you for your replies! They are very informative. I wish though to clarify a few more things.

I forgot to mention that I need to run it also at the lowest RPM possible. How can I demand, say, 1.5kW at a speed of less than 2000 without the engine shutting down?

 

[moon161]

2000 RPM? Shouldn't be bad.

If it gets enough air at that speed to develop the power, or w/o lugging badly, the governor in the injection pump should handle it.

If you have problems w/ smoothness, you could add weight to the flywheel so that you have enough rotational energy to make it around twice without appreciable drop in RPM.

Really, consider the cost of modifications compared to whatever you'll be saving by running it as is.

 

[jmw]

Like a Bolinder?

http://www.bolinder-engines.info/semidiesel/semihistory.html

JMW

http://www.ViscoAnalyser.com

 

[Tmoose]

what is the engine driving?

 

[Gearloose1]

I am not sure what you might gain by reducing cooling.

A properly designed cylinder / piston / cylinder head have an insulating blanket of air that blocks a lot of the heat loss.

If the injectors are good, they are suppose to keep fuel away from the cylinder walls, where they both cool and wash down the walls of lubricant.

The best gain in efficiency may be lower RPM, as pumping losses (big) rises exponentially with speed.

Can you gear it to something between 1,200 to 1,500 rpm running with your load?

 

[BrianPetersen]

The only gain by reducing cooling, is reducing the parasitic loss associated with driving the cooling fan. If the engine is running at less than full load and *never* runs at full load, it doesn't need the full air flow rate. Yes, it will only make a very small difference.

 

[patprimmer]

Running the cooling system at considerably reduced speed on an air cooled engine can make a significant difference to power, so it should also make a considerable difference to fuel efficiency for 2 reasons.

1) The mechanical efficiency is increased by the power not used to drive the fan so hard.

2) The thermal efficiency is increased by reduced cooling of the gas that is driving the piston down.

Regards
Pat
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[Gearloose1]

The issue of power lost via Fan can be addressed with a electrically operated (or thermal / mechanical viscous coupling) fan.

I can see the gain from the electrical at moderate cost.. but is it really worth it?

 

[patprimmer]

If it's running at constant speed and constant load you just cut the fan blades down at no cost, or change pulleys to drive it slower at minimal cost.

You run it so it cools adequately on the hottest day. If it has a thermostat you use that to stop over cooling on cold days.

Regards
Pat
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[jmw]

To hear the Bolinder engine in operation:

http://www.youtube.com/watch?v=fZ4ORUZ41K0

I've heard one running in a barge where it would fire a couple of times, run on under the influence of its flywheel fire again, quite again.... more like this one working hard....

http://www.youtube.com/watch?v=nw4fw_pkioM

or this 9hp which goes ffrom low load to load to low load again:

http://www.youtube.com/watch?v=cdMxgI2ywYo&feature=related

JMW

http://www.ViscoAnalyser.com