Ethanol can replace gasoline in a spark-ignition engine, but a litre holds only about two-thirds the energy (21.1 MJ against about 32), so the engine burns roughly 1.5 litres of ethanol for each litre of gasoline it replaces. A diesel engine cannot run on ethanol; use biodiesel there. Mixed into gasoline at 10-20%, ethanol needs no engine changes, while neat ethanol needs bigger jets, more spark advance and ethanol-proof fuel lines.
Part of Ethanol Fuel Production
Engine use of ethanol covers running petrol engines on blends or neat ethanol, the changes that need, and what a kilometre costs in feedstock.
Three Ways To Use It
| Way | What it is | What it needs |
|---|---|---|
| Blend (E10-E20) | 10-20% ethanol in gasoline | no engine changes, per the parent; dry ethanol only (Ethanol in Gasoline Engines) |
| Neat ethanol (E100, or E85) | ethanol alone, or 85% with gasoline | bigger jets or longer injection pulses, earlier timing, new seals (Carburetor & Injection Modifications, Fuel Line Material Compatibility) |
| Diesel engine | cannot burn ethanol | use biodiesel instead (Biodiesel Production) |
Ethanol suits spark-ignition engines because it resists knock (octane 108-110 RON). It starts poorly in the cold. The corpus’s overview of alcohol as a fuel is Fuel Applications.
What A Kilometre Costs, In Food
Energy: 21.1 ÷ 32 = 0.66, so for the same energy you need 32 ÷ 21.1 = 1.52 times the volume, about 1.5 litres of ethanol per litre of gasoline. The parent says ethanol is “roughly 70% of gasoline’s energy” and then “30% higher fuel consumption”; 70% energy needs 1 ÷ 0.7 = 1.43 times the fuel, which is 43% more, not 30%. Higher compression and better knock resistance can win back some of this in a modified engine.
Example for a vehicle that uses 10 litres of gasoline per 100 km (an assumed figure; use your own):
- Ethanol: 10 × 1.52 = 15.2 litres per 100 km.
- Corn: at 2.5-2.7 kg per litre (Feedstocks), 15.2 × 2.5 = 38 kg to 15.2 × 2.7 = 41 kg per 100 km.
- Food energy: 15.2 litres × 9,100-9,800 kcal = 138,000-149,000 kcal, which is 49-53 person-days at 2,800 kcal a day.
A 100 km car trip on grain ethanol uses about as much food energy as feeds one person for seven weeks. Run vehicles on ethanol made from waste or surplus, not from the grain store.
Common Mistakes
- Starting a diesel engine on ethanol. It will not ignite properly and can damage the engine.
- Planning fuel stocks at 30% extra. Plan on 43-52% more by volume.
- Putting wet ethanol in a gasoline tank. It separates from the fuel (Dehydration to Fuel Grade).
Engines and fuel
Run engines outdoors or in a space with a clear exhaust path: exhaust carbon monoxide kills silently. Ethanol burns with a pale, hard-to-see flame and its vapour is explosive at 3.3-19% in air; a leaking fuel line on a hot engine is a fire (Fire Safety). The corpus’s guides to using engines as power sources are Converting a Vehicle Engine to Stationary Use and Internal Combustion.
What’s Next
- Learn next: Ethanol in Gasoline Engines, for blends and the lean shift
- Combine with: Wood Gas Vehicles, the other petroleum-free vehicle fuel