Cleaned producer gas runs a spark-ignition engine through a mixing valve where the gas pipe meets the air intake, and the engine is started on petrol and switched over once the gas is good. The engine will make only 40-60% of its rated power, needs about 10-15° more ignition advance because the gas burns slowly, and a diesel engine needs a small pilot injection of diesel to ignite the gas at all.
Part of Biomass Gasification
The engine connection is the mixer, the changes made to an engine’s ignition and compression, and the power it can then deliver on producer gas.
The Engine Is Fed Gas And Air Instead Of Petrol Vapour
A petrol engine takes in air plus fuel from a carburettor. For producer gas the engine takes in air plus gas, and a mixing valve where the gas line meets the air intake sets the proportions. The gas is about half of the mixture by volume (43-53% from the composition range worked out in Mixing Valve & Air-Fuel Ratio), so the engine’s air supply is displaced by gas, and that is part of why power falls.
Three things differ from running on petrol:
- A mixer that controls gas and air (Mixing Valve & Air-Fuel Ratio).
- Engine adjustments for a slower-burning fuel: ignition advance of 10-15° and, if possible, a higher compression ratio (Engine Modifications).
- Lower power, 40-60% of rated, which sizes the whole job (Power Output Derating).
Method: The Switch-Over
- Start the gasifier and run it with the start-up blower until it makes good gas (Startup Sequence (20-30 Minutes)). Flare the gas outdoors to check it.
- Start the engine on petrol and let it warm.
- Open the gas valve gradually and close the petrol supply as the engine settles on gas.
- Adjust the mixer for the smoothest running. Too much gas gives misfires, and too much air gives overheating and a weak, slow burn.
- Before stopping, switch back to petrol for the last 2 minutes, as the second carrier does, so the engine is not left holding gas.
Diesel Engines Are Dual-Fuel
A diesel engine does not spark-ignite, and producer gas does not compression-ignite reliably, so the engine keeps injecting a little diesel to light the gas. The parent says a pilot of 5-15% of normal diesel consumption; I could not source that fraction and it is likely to be the optimistic end, because the amount of pilot needed does not fall in proportion at light load. Treat the diesel saving as unverified until measured.
Common Mistakes
- Connecting an engine before checking the gas. Tarry gas fouls an engine in one session.
- Leaving the mixer at the first setting. The right setting changes with load and temperature.
- Piping the exhaust into a shed. Engine exhaust on producer gas still carries carbon monoxide.
Safety
The engine bay joins the gas line, and the exhaust is poison too
Producer gas is about 18-22% carbon monoxide by volume. Never run the engine on gas indoors, in a garage, in a shed or in any enclosed yard, not even for a minute “to warm up”, and keep the exhaust pointing away from people and buildings. A backfire through a gas-filled intake can ignite gas in the line, which is a vessel with a flammable mixture in it. Start-up gas is the worst: cool, rich and nearly all carbon monoxide. See Carbon Monoxide Risks.
What’s Next
- Learn next: Mixing Valve & Air-Fuel Ratio — setting the mixture
- Combine with: Converting a Vehicle Engine to Stationary Use — mounting a salvaged engine for generator duty