This position paper describes how gas engines are influenced by the quality of the gaseous fuel provided. This topic is becoming increasingly important as highly fluctuating renewable energy resources call for quick reacting and reliable back-up power often provided by gas engines.
Important aspects of the quality of a gas, in addition to the heating value and the Wobbe Index, are: the composition of the combustibles which influences the combustion behaviour and knocking characteristics, the rate of change of the gas composition with time, and the concentration of impurities, for example sulphur. The knock characteristics of a gaseous fuel can be calculated for a given composition and the calculated Methane Number (MN) indicates the resistance of the given fuel to end gas knock. The Methane Number is comparable to the octane number for liquid fuels, which is typically used with gasoline fuels for passenger cars.