[Digestion] Sucessful small engine Conversion experience?

[Jim and Amy Rankin]

Hi Mike,
The biogas conversion would be easier on an engine that is already setup for 
propane vapor or Natural gas use.  then it's a matter of opening the gas 
adjustment on the vapor mixer/carburetor to account for the %CO2 that's 
mixed with the biogas compared to pure LPG vapor or natural gas.

If you are likely to need more power than your biogas can supply, you might 
want to supplement a diesel engine (maybe like one of the Lister or 
"listeroid" generators) with biogas.  These engines are very long lived and 
reliable running on diesel, biodiesel or vegetable oil and many are used 
around the world for the only source of power as opposed to the common small 
portable backup/emergency set which probably will not ever run more than 
10's of hours before neglect and age result in it being junked if it doesn't 
fail on it's own while under load.

Supplementing a diesel engine can be pretty simple if the load is stable, 
you adjust the flow of biogas into the air intake of the diesel engine after 
it is started, running at the desired speed and the load applied.   As the 
biogas comes in, the diesel governor will cut back to keep RPM from rising. 
If the biogas runs low or load increases, the governor will feed more diesel 
fuel and attempt to meet the demand.  If the demand for power is greater 
than the engine can supply,  it may overheat since it's essentially being 
overfueled even though the diesel injection system may not have reached it's 
set fuel limit.

This works well on a fairly constant load maybe like a battery charging 
setup but would not work where load varied down.  If load is allowed to 
decrease, there has to be some way to cut back on the biogas so the diesel 
doesn't overspeed.  I expect it could be done with a separate governor that 
just metered the biogas into the diesel intake as opposed to the normal 
spark engine governor that controls the throttle plate.

You would have the expense of the diesel essentially running at idle speed 
just to ignite the biogas, but you get a heavy duty/continuous duty engine, 
backup fuel capability and the ability to burn very low % methane biogas if 
that were to be an issue.   If you use a spark engine, you probably should 
oversize it by about 100% compared to one that is rated on gasoline or LPG.

You don't mention what size generator you are considering.

Jim


> I am considering an environmental proposal in a few months that could give 
> our property more power through a hybrid arrangement in tandem with an 
> existing solar energy system.
>
> Can anyone tell me of their experiences converting a small generator to 
> run on biogas, and maybe of the modification experience on a standard "off 
> the shelf" genset?
> I would appreciate any papers, documents and other info on "real life" 
> exercises.
>