Diesel generator conversion to wood gas

I have purchased a Onan MDJC 10KW (@50 HZ) generator, it is a 4 cylinder 1.9 litre indirect injection Diesel. At present I have a 4 KW Genrac made generator with a 4 cylinder Nissan engine, this works well but is not big enough. I run through a inverter charger that draws nearly 2 KW for battery charging this does not leave sufficient power for running the house.

My Plan is to machine out the precombustion chambers and make spark plug holders to go in place of the injectors. The engine is 19 to 1 compression from my research it seems 17 to 1 is good for wood gas. Also this high ratio will give higher efficiency, I know some on this forum say efficiency does not matter but why spend more time preparing fuel than is necessary. If needed I will add a copper spacer to reduce the compression ratio as I want to get the spark plug tip as far into the main combustion area as possible.

For ignition I plan to scrap one fuel injection pump that is leaking Diesel anyway (I have a spare engine) and make a electronic trigger for a 4 coil pack. Other than that all should need is to do is add a wood gas carby and change the crankcase ventilation. As at present it draws directly in to the intake port in the head, here it would be under vacuum after fitting the carby.

Has anyone tried doing this with a Diesel?


Hey GaryH.
Sound like a workable plan man. I’ll be interestied to see your results.

Look here:
for description and pictures of JohanL sparkconverting his 65 year old David Brown 3 cyclinder diesel tractor. Sure to have been IDI. He used a Volvo 6 cylinder distributor using every other terminal post.

Another three pages of references with pictures is in Vesa Mikkonens book. I’l paraprase a few supportive sentances.
IDI, pre-chamber he says to machine open the prechamber to the main combustion chamber. DI, direct injection to open up the in piston top combustion chamber. Use these changes for compression ratio modifing. Says 17/1 as max before detonation. Says woodgas with higher percentages of carbon dioxide are more detonation proof. Woodgas with increasing proprtions of hydrocarbons cut the octane number down requiring a lower compression. He is speaking from direct expereinces.
He also favors diesel engine spark converting versus pilot diesel ignition and recommends electronically triggered coil pacs for the sparks.
Neither state any ignition timing ranges recommendations.
I figure you will need at least 30 degrees total range from cranking starting up for a 3000 RPM engine range of operation.

Do you think your woodgas generator/hearth will supply enough woodgas volumn for this larger engine??

Ha! Ha! SeanF for vehicle use VesaM is recommending looking into the old 80’s diesel converted Olds engines converted back to spark ignition as common GM chassis compatible.

Steve Unruh

Re $$$$$$$$ all I can say to that is LOL, Will cost me very little, I need to buy a coil pack, electronics components, spark plugs and not much else. As I have a free access to lathe and being a Fitter and Turner in my past I doubt I will spend more than $200.

Steve that link says "Not Found

The requested URL /dagbok/mera/19e.shml was not found on this server.’

Could confirm that is the correct address.

The genset runs at 1500 RPM and will have infinite timing adjustment available. Plan is to advance it a little then just watch the governor while adjusting to get the least throttle opening.

My gasifier is a GEK with TOTTI additions, it has a 75 MM restriction which APL say will run 10 KW. I won’t be running it that hard most of the time will be around the 3 to 7 KW range.

Vedbil Works, don’t know why this link failed.

Good Morning GaryH.
Direct search “Woodgas David Brown Diesel Johan” for a direct useable link.

Then you have to dig down three-four layers to get past the vehicle projects: Home Page in Sweedish -> L.H upper corner Flag icon for English -> R.H. side halfway down for the “Carbon Nuetral Farming” -> L.H sidebar on that page for the oldest dated tracor link. Rest assured the converted diesel tractor tractor info and pictures are there. Cylinder head picture with the spark plug shows that this may have been a direct injection engine.

For this application your will find you will be much happier with a 100mm restiction in your GEK. Direct expereinces here.

Steve Unruh

I have started on the cylinder heads, I need to gain some volume in the combustion chamber to compensate for what is lost in the precombustion. Over the next few days I will be making inserts to go in where the injectors used to go. These will completely fill the precombustion chamber and just the tip of the spark plug will protrude through the hole you can see.

Steve could elaborate on what difference the larger restriction will make.

Hello GaryH.
Nice picture set. Really shows commitment with no turning back.

Restrictions have a primary purpose to be sure and have all upper system superheated gasses channeled into the center and forced through the piled up bed of glowing hot charcoal for Reduction to the fuel gases of H, CO and CH4. Outer edge, or char pile internal “channeled” bypassed upper gases remain UnReduced noncombustable watervapor and carbondioxide. Waste of good system heat and motor fuel potential.
2nd primary use of the restiction is to support the upper system weight of woodfuel in process pyrolization and oxidization process so this weight is not all supported by the heat softened metal grate and grate supports.
The problem that the restiction introduces is that in addition to flowing the upper system gases (the cold gas calculated opening) it has to also flow the oxidization zone produced now nearly white hot heated cooked out wood char chunks and any burnt freed up mineral ash.
Very easy to have a gases/solids flow clog at the restiction and not realize it until the whole system balances of gases, solids and heats crashes.
Much easier in an active grate system like a GEK based to build the grate heavier with slotted openings to restrain the char chunks above and be able to take more of the upper system fuels material weight.
And then control things with sensed pressures/temperatures by variable active grate activation.
Direct expereince here with active grates.
Passive grating works with but in my expereinces requires strict fuel type/sizing and system flow rate restictions to be able keep things moving along. Passive grating you have to to willing to do a lot of slipped char with ash removal to keep things marching through the whole system.
No grate/no restictions systems also work like the Mukunda’s and I believe Greg Manning’s by augering out a percent of the lower end mix of char-ash with new upper system fuel reloads. Then they cool, wash out the char from this removed mix for higher value use or use this char/ash mix for direct soil amendment.

You will find even the change from an ash clearing pulsating single cylinder engine to evened out vacumn sucking multi-cylinders will change your grate ash clearing operating neededs. I did.

You cannot calulate at these levels of developement. Do lots of operating hours runs to set up empirical results driven ranges for your systems, your fuels and your specific useages. Change any one thing will introduce a different range of possibilities - favorable and unfavorable.
Steve Unruh

Hi Steve,

I have a 2nd engine with a failed oil pump for parts so I have spare heads etc. The engine has 2 heads and at this stage I have only worked on one and have 3 that I have not touched as yet.Until I have one head finished I won’t be touching the others. I plan to sell the injectors and fuel pump so it will never go back to running on Diesel anyway.

At present I have a 4KW 4 cylinder generator running off the GEK. It has been performing very well with the 75mm restriction while running at full load for many hours at a time. When I get the bigger Onan operating I will try it as it is and modify it as needed. As per your advice i will be changing one thing at a time. Previously I had some auger issues that resulted in a larger clinker at the nozzles and down into the restriction. But since getting the auger sorted out and using sorted wood chips I have had no further issues in the grate or restriction.

More power to you Gary, hopefully wood power. You are doing more than I could ever hope to try, but I really appreciate the R & D that’s going on there. Good luck.

Hi Carl,

I am going mostly off of research I have done with Google. APL and Ken Boak has given me the most information with their efforts documented on the APL website.

After looking at how to control triggering ignition I have decided use a Toyota ignition coil for simplicity and reliability.