The Rate-Controlled Constrained-Equilibrium Combustion Modeling of n-Pentane/Oxygen/Diluent Mixtures

Rate-controlled constrained equilibrium (RCCE) is a reduction technique used to describe the time evolution of complex chemical reacting systems. This method is based on the assumption that a nonequilibrium system can reach its final equilibrium state by a series of RCCE states determined by maximizing entropy or minimizing relevant free energy. Those constraints are imposed by some small number of slow reactions. Much research has been done on this method and many RCCE models of $C1−C4$ hydrocarbon fuel combustion have been established by the previous researchers. Those models show good performance compared with the result of detailed kinetic model (DKM). In this study, RCCE method is further developed to model normal pentane (n-$C5H12$⁠) combustion with least number of constraints. The chemical mechanism for DKM contains 133 species and 922 reactions. Two sets of constraints were found during the study: (1) 16 constraints for the normal pentane and pure oxygen mixture and (2) 14 constraints for the mixture of normal pentane and oxygen with argon as diluent. Results of the first constraint set were compared with result of DKM and results of the second constraint set were compared with those of DKM and experimental data by calculating their ignition delay times. Comparisons showed that the first set of constraints had relatively good accuracy and the second set of constraints agreed very well with the experimental data.