How is air-to-fuel ratio generally expressed?

The air-to-fuel ratio is typically expressed as a mass ratio of air to fuel. This method provides a more accurate representation of the combustion process because the mass of the reactants is what fundamentally governs the stoichiometry of the reaction.

When calculating combustion and efficiency, understanding the relationship between the mass of air and fuel is critical. This metric allows for more precise control of the engine or burner operation and optimization of combustion efficiency, reduction of emissions, and performance optimization.

Furthermore, mass ratios account for the differences in densities between air and fuel, which can vary significantly. This is particularly important in applications where fluctuations in temperature and pressure can affect the density of the air involved. Expressing the air-to-fuel ratio in terms of mass ensures consistent and reliable performance across varying operating conditions.

The other choices, while they represent different relationships, do not convey the most pertinent information needed for operational efficiency and combustion calculations in mechanical and gas systems.