Theoretical and experimental studies have shown that spark-ignition engine fuel composition can have an influence on performance and exhaust emissions. Studies have been made on gasoline, alcohol, hydrogen and ammonia fuels. Energy content and carbon to hydrogen ratio both are influential in determining engine performance and exhaust content of potential air pollutants exhausted into the atmosphere. Neither hydrogen nor ammonia can produce carbon monoxide or unburned hydrocarbon and theoretically should also give less nitric oxide, at most conditions than do octane and alcohols fuels.

Some possible measurements are made using gasoline, methanol and ethanol fuels. These measurements show that there is an increase in engine thermal efficiency and less nitric oxide and carbon monoxide when using methanol and ethanol fuels than that of gasoline. These experiments confirm the theoretical results obtained.