gas-fired turbines, the more common terms are percent excess combustion air and percent stoichiometric air. For example, excess combustion air of 15 percent means that 15 percent more than the required stoichiometric air (or 115 percent of stoichiometric air) is being used. A combustion control point can be defined by specifying the percent excess air (or oxygen) in the oxidant, or by specifying the percent oxygen in the combustion product. An air–fuel ratio meter may be used to measure the percent oxygen in the combustion gas, from which the percent excess oxygen can be calculated from stoichiometry and a mass balance for fuel combustion. For example, for propane () combustion between stoichiometric and 30 percent excess air (AFRmass between 15.58 and 20.3), the relationship between percent excess air and percent oxygen is: See also Adiabatic flame temperature AFR sensor Air–fuel ratio meter Mass flow sensor Combustion Stoichiometric air-to-fuel ratio of common fuels References External links HowStuffWorks: fuel injection, catalytic converter University of Plymouth: Engine Combustion primer Chemical reactions Engineering ratios Engine fuel system technology Engines