An engine can run without petroleum on three locally made fuels, and each needs its own preparation and its own delivery to the cylinder: wood gas from a gasifier, ethanol from fermentation and distillation, and biodiesel from oil or fat. The fuel sets the power: gas and air carry about 65% of the energy of petrol and air in the cylinder, and an ethanol engine burns roughly 1.5 litres for each litre of petrol it replaces.
Part of Internal Combustion
The fuel options for a rebuilt engine, what each costs in power and effort, and the parts that deliver each to the cylinder.
Three Fuels, Three Preparations, Three Deliveries
The carrier ranks the realistic options by ease. Gasoline degrades within one to two years and diesel within five to ten with stabiliser, so stored fuel is a stopgap, not a plan.
| Fuel | Made by | Suits | What the carrier reports |
|---|---|---|---|
| Wood gas | Partial burning of dry wood in a gasifier | Spark-ignition engines | 40-60% of gasoline power; about 1 kg of dry wood per horsepower-hour |
| Ethanol | Fermenting and distilling sugar or starch | Spark-ignition engines | About two-thirds the energy per litre; 70-80% of gasoline power with tuning |
| Biodiesel | Oil or fat with methanol and lye | Diesel engines | Energy nearly equal to petroleum diesel |
The 1 kg per horsepower-hour is 1.4 kg per kWh, as the carrier works out. Detail on each fuel is in its own page: Wood Gas Generation, Alcohol Distillation, and for biodiesel the corpus article Biodiesel Production. Diesel Cycle covers the engine side of biodiesel.
Delivery Differs By Fuel
- Liquid fuel for a spark-ignition engine goes tank, filter, line and carburetor, which meters it into the air stream; see Carburetor Design. Ethanol attacks natural rubber and some plastics, so lines and seals must suit it, as Fuel Line Material Compatibility sets out.
- Gas has no tank in the usual sense. It flows from the gasifier through a cooler and filters to a mixing valve that sets the gas-to-air ratio, and the engine takes it straight in; see Mixing Valve & Air-Fuel Ratio.
- Diesel-type fuel goes through filters to an injection pump and injector, not a carburetor.
The delivery system matters as much as the fuel. A good fuel through a poor system gives a rough, weak engine, and any restriction or dirt shows up as lost power.
Worked Example: Why Each Fuel Costs Power Or Volume
Producer gas. The corpus compares the charge in the cylinder, not the fuel in the tank, in Power Output Derating: gas and air carry about 2.46 MJ/m³ against 3.80 for petrol and air.
- Ratio: 2.46 ÷ 3.80 = 0.647, which is about 65%.
- That ratio is the cap on the power of a converted engine before real losses reduce it to the carrier’s 40-60%.
Ethanol. The carrier gives about two-thirds the energy per litre of petrol.
- To get the same energy: 1 ÷ (2/3) = 1.5 litres of ethanol per litre of petrol replaced.
The settlement has to grow or collect that extra volume, and the tank and carburetor have to pass 1.5 times the liquid. The jet-size arithmetic is in Carburetor & Injection Modifications.
Common Mistakes
- Relying on stored fuel. It spoils; plan the new supply before the old runs out.
- Leaving rubber lines in an ethanol system. They swell, crack and leak.
- Feeding gas without cooling and filtering. Tar and ash destroy rings and valves.
- Expecting full power. Each of these fuels gives less than petrol, and the engine must be matched to it.
Safety
Fuel is the most flammable thing in the engine shed
Ethanol vapour ignites between 3.3 and 19% in air from a flash point of about 13 °C and burns with an almost invisible flame, according to the corpus article Fire Safety; keep it away from flames and sparks and store it outdoors. Wood gas is about a fifth carbon monoxide and kills without warning; see Wood Gas Generation. Methanol, used in making biodiesel, is toxic through skin and lungs. Never smoke or light a flame while fuelling or looking for a leak.
What’s Next
- Learn next: Alcohol Distillation — making ethanol fuel
- Combine with: Carburetor Design — metering it into the engine