The development of model fuels requires detailed chemical reaction models of all fuel molecules involved as well as all their intermediate and final products. Simplified models, which are necessary for use in numerical methods, must be developed on the basis of the detailed mechanisms which cover the entire parameter range of technical combustion systems.
The present research focus is the development of a detailed chemical kinetic reaction database that accurately describes heat release and pollutant formation modeling in gas-turbine combustors. The structure of this database, with which the oxidation of various gaseous and liquid fuels can be described, is pictorially represented in Fig.1. The development principle of this database is based on continuous adaptation, validation, and optimization of the descriptions of the various hydrocarbons’ kinetic reactions (see Fig.2). The current reaction database DLR includes an inherently consistent body reaction model with submodels for H2, CO, CH4, CH3OH, C2H4, C2H5OH, C2H6, C3H8, n-C4H10, C7H8, cy-C6H12, cy-C9H18, n-C7H16, i-C8H18, n-C10H22, i- C10H22, i-C11H24, n-C12H26 und n-C16H34. Additional sub-models describe the formation of NOx and PAH. This model describes the heat release, ignition delay, flame speed, PAH formation (see Pollution Formation) for each of the above-mentioned hydrocarbons as well as technical fuels (represented by model fuels containing mixtures of the individual hydrocarbons).
The requirement for efficient reduction of detailed reaction mechanisms, which is imperative for CFD modeling in combustor design, necessitates the development of appropriate mathematical methods. The development strategy for these reduced reaction mechanisms is shown in Figure 3.
The developed programs RedMaster and QSSGlob automatically reduce the detailed reaction schemes to skeletal mechanisms (RedMaster) and then further to global reduced mechanisms (QSSGlob) without significantly reducing their predictive ability. The RedMaster program determines and eliminates unimportant reactions and species using information obtained during select times of interest for all chosen modeling conditions. The QSSGlob program produces globally reduced reactions by analyzing the time scales of combustion processes. With these tools, complex chemical-kinetic processes, which occur during fuel oxidation and fuel pyrolysis, are made available to, and enhance, the predictive ability of numerical simulations.