Fuel Efficiency

Fuel efficiency is a form of thermal efficiency, meaning the efficiency of a process that converts chemical potential energy contained in a carrier fuel into kinetic energy or work. Overall fuel efficiency may vary per device, which in turn may vary per application, and this spectrum of variance is often illustrated as a continuous energy profile. Non-transportation applications, such as industry, benefit from increased fuel efficiency, especially fossil fuel power plants or industries dealing with combustion, such as ammonia production during the Haber process.

In the context of transport, fuel economy is the energy efficiency of a particular vehicle, and is given as a ratio of distance travelled per unit of fuel consumed. Fuel economy is expressed in miles per gallon (mpg) (prevalent in the USA and UK, using their respective definitions of a gallon) or kilometres per litre (km/L) (prevalent in the Netherlands, Denmark and in several Latin American or Asian countries such as India, Japan, South Korea). The reciprocal ratio, "fuel consumption", is usually expressed in liters per 100 kilometers (L/100 km) (common in Europe, Canada, New Zealand and Australia) or litres per mil (Norway/Sweden).

Variations on a vehicle's fuel efficiency include weight-specific efficiency for freight, and passenger-specific efficiency (vehicle efficiency / number of passengers).