What does the term "combustion efficiency" refer to?

The concept of "combustion efficiency" is primarily related to how effectively a fuel burns to produce energy. It measures the ratio of useful energy output (in the form of heat, for instance) to the energy input from the fuel consumed. This means that it assesses how much of the energy contained in the fuel is converted into usable energy versus how much is wasted.

Taking this into context, the completeness of fuel combustion refers to how well the fuel reacts with oxygen, which is a related but separate concept. The speed at which fuel burns pertains to the rate of combustion, not its efficiency. Finally, the total amount of gas used provides a measurement of consumption but does not directly correlate to the efficiency of energy conversion. Thus, the correct understanding of combustion efficiency focuses on the relationship between energy input and output, which is encapsulated in the ratio mentioned in the chosen answer.