Running an IC engine on compressed propane/butane

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xander janssen

Well-Known Member
Jan 5, 2012
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Hi there,

I was wondering if I can run my IC engine 25 mm (1 inch) bore on propane or butane (or mixture) to avoid having the need for a carburetor. Just running idle is sufficient, no need for various RPMs as it will only be used to run the engine for demonstration only.

My idea is as follows (which works at real size engines):

- Use liquified propane/butane (or mix) in a camping stove type cartridge
- Reduce the pressure using a commercial available (tested, certified etc) pressure reducing device to ~30 mbar (0.4 psi)
- Make a cam operated valve that releases the gas only during (part of) the intake stroke into the intake manifold

This should avoid any flooding of the engine and for my 2VD5 engine allow to run without a carburetor which spoils the "Diesel" engine look of the engine.

Anyone ever tried this who can help me with the design/principle of the valve? This is to my opinion the most challenging part as it should not leak during operation nor during the closed phase to avoid dangerous situation of leaking flammable gas.


Some people have a demand regulator in the gas line that uses a small diaphram that opens the valve when the vacuum in the cylinder draws in.
I have done a couple where the inlet valve seat be it angled or flat has several holes for air as well as a small one for the gas so as the valve opens you get a small amount of gas mixing with the air that is closed off again as the valve closes.

the main thing is to regulate the amount of gas not so much the pressure I use a regular 2-4bar regulator but a very fine needle valve to adjust teh amount of gas



Wow, great idea to have it combined in one valve and the straight air inlet channels.

What is roughly the diameter of the valve? Just an indication is enough to get a feeling for the other dimensions.

Do these combined valves directly replace the intake valves or is there another intake valve between this combined valve and the the combustion chamber?
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You can use a screw-on gas pressure regulator/shutoff valve found on small portable gas cooking grills. This keeps pressure low at about 4" of water column which is adequate. You will need, or you can make a demand regulator which allows fuel to flow only on the engine intake (suction) stroke. See link. It also keeps fuel from flowing when the engine stops. The needle valve in the carb needs to be opened a few more turns to make up for the reduction in BTU's of the gaseous fuel.

This simple system is best used on constant speed engines and also works on H&M engines.
Use a small inexpensive Garretson demand regulator to prevent flooding the engine or having fuel gas escape into your shop.
If you build a non-mixing cam-operated fuel valve, design it such that the fuel gas supply is above the valve head so that leakage past the valve stem is eliminated. That's how it was done "back in the day".

You'll find that model engines perform very well on propane.
Most of marine diesel engines are now dual fuel engines. Running on both oil or natural gas.

The cast iron one with the flat valve has 7 x 1/8" air holes and one 1/32" hole for the gas. The brass one has six 3/32" air holes and one 1/32" gas hole

Both are the only actual valve there is no other inlet valve. The iron one is for a hot tube ignition engine of 1.5" bore x 1.5" stroke and the brass one for ayet to be finished spark ignition 1.5" bore x 2" stroke engiene

Iron one in action, at about 50sec in you can see the atmospheric inlet valve opening.

This is another way to do it and works much like a Lunkenheimer carb where there is a valve that is lifted off it's seat by the intake stroke allowing gas in via a small hole 0.5mm in the seat. Gas from the left, air from the right. You can see the valve opening about 1min into the video