Numerical and Kinetics Study of CH4 + H2+ O2 + CO2 LaminarPremixed Flame Speed with Directed Relation Graph Method

In direct numerical simulation of reactive flows, detailed chemical kinetic mechanisms when coupled with transport process models require tremendous computational resources. These kinetics mechanisms consist of large numbers of species and elementary reactions. In order to lessen the computational cost in numerical simulations, skeletal mechanisms are used instead of detailed mechanism. The algorithm of Directed Relation Graph (DRG) is used for detailed mechanism reduction of (CH4 + H2) + (O2 + CO2) combustion in overall linear time operation. In this study the algorithm of DRG is applied to a laminar premixed flame to determine unimportant species. Those elementary reactions that consist of unimportant species are eliminated from kinetics mechanism. Skeletal mechanisms were generated with DRG under various equivalence ratios. The governing equations of laminar premixed flame were solved by PREMIX solver. The selected values of equivalence ratios were varied from 0.6 to 1.6. Temperature was 1000 Kelvin and pressure was 1 atm. The hydrogen content in the fuel was varied from 0% to 35% and the oxygen content in the oxidizer was 31.55%. These mixtures could be formed when oxy-fuel combustion technology is combined with hydrogen enrichment. Values of laminar premixed flame speed calculated under these conditions for detailed and skeletal mechanisms. The results of skeletal mechanisms were validated by experimental values and detailed chemical kinetics result. It was observed that the accuracy of skeletal mechanisms could be bounded by user-specified error threshold values. DRG method proved to be computationally more efficient, because it directly eliminates unimportant species instead of elementary reactions from the full mechanism.

Keywords:

Reactive flow , Directed relation graph (DRG) , Skeletal mechanism , Premixed laminar flame