One of the main goals in developing more advanced technical combustion technologies is the cost-efficient use of fuels of different quality, in addition to improve their efficiency and besides reducing their pollutant emissions. Depending on the design concept of a specific combustion process, in a gas turbine or in an engine, the composition of any fuel mixture must fulfill certain specifications. This ensures that combustion proceeds in an optimal, safe and reliable way so that the combustion chamber is not damaged which would impose enormous costs on manufacturer and operator.
Natural gas - considered as a “simple” fuel - illustrates the importance of fuel quality for present-day power generation. The composition of a natural gas mixture varies strongly depending on its source. The suppliers purify the natural gas and usually mix natural gases of different sources, mainly with regard to the calorific value, before delivering the “final” natural gas to the customer (private households or power generation industry). Therefore, the exact composition of a natural gas mixture is location-specific. This raises the question for gas turbine manufacturers which specifications the local natural gas at the site of operation must fulfill. What is, e.g., the minimum fraction of methane or the maximum fractions of ethane and higher hydrocarbons possible? This is important because the higher the fraction of ethane and higher hydrocarbons, the higher the risk of flashback or self-ignition of the premixed natural gas / air blend, with a potential of severe damage.
Nowadays, to define the operational parameters, detailed chemical kinetic reaction mechanisms can be used as an essential step in the design of a combustion chamber concept. By using reliable and validated reaction models, it can be assessed how the combustion properties of the fuel mixture are influenced by its specific composition, at basic given conditions (e.g. preheat temperature, pressure, and fuel-air ratio). This strategy helps to identify critical operating points for a predetermined fuel composition, even at this early stage of development. Thus, the number of expensive component tests which are ultimately necessary in order to specify the fuel quality can be reduced.
Providing validated chemical reaction mechanisms for natural gas is therefore one of the main tasks of the chemical kinetics group. By using these reaction mechanisms, it is possible to obtain an improved CFD design and to optimize technical combustion processes with regard to the fuel quality of conventional and alternative fuels or of additives.