VALIDATION OF THE ASVDADD CONSTRAINT SELECTION ALGORITHM FOR EFFECTIVE RCCE MODELING OF NATURAL GAS IGNITION IN AIR

摘要

The Rate-Controlled Constrained-Equilibrium (RCCE) model reduction scheme for chemical kinetics provides acceptable accuracies in predicting hydrocarbon ignition delays by solving a smaller number of differential equations than the number of species in the underlying Detailed Kinetic Model (DKM). To yield good approximations, the method requires accurate identification of the rate controlling constraints. Until recently, a drawback of the RCCE scheme has been the absence of a fully automatable and systematic procedure capable of identifying the best constraints for a given range of thermodynamic conditions and a required level of approximation. A recent paper [1] has proposed a new methodology for such identification based on a simple algebraic analysis of the results of a preliminary simulation of the underlying DKM, focused on the behaviour of the degrees of disequilibrium (DoD) of the individual chemical reactions. The new methodology is based on computing an Approximate Singular Value Decomposition of the Actual Degrees of Disequilibrium (ASVDADD) obtained from the DKM simulation. The effectiveness and robustness of the method has been demonstrated in [1] for some cases of methane/oxygen ignition by considering a C1/H/O (29 species/133 reactions) sub-mechanism of the GRI-Mech 3.0 scheme and comparing the results of a DKM simulation with those of RCCE simulations based on increasing numbers of ASVDADD constraints. The RCCE results are in excellent agreement with DKM predictions for relatively small numbers of RCCE constraints. Here we provide a demonstration of the new method for some cases of shock-tube ignition of a natural gas/air mixture, with higher hydrocarbons approximately represented by propane according to the full (53 species/325 reactions) GRI-Mech 3.0 scheme.