1. Definition of fuel efficiency:
Fuel Efficiency is the proportion of energy released in the process of a fuel combustion, which is finally converted into useful work. It is usually used as a parameter to value the performance of a car or other vehicles.
2. Two ways to express fuel efficiency:
One is units of fuel per fixed distance, such as gallons/100 kilometers (gal/100 km) and miles/gallon[US] (MPG).
The other is units of distance per fixed fuel unit, such as kilometers/gallon (km/gal), kilometers/litre (km/L), miles/litre (mi/L).
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