Accelerating laminar flame speed solvers for large kinetic mechanisms*

A fast solver is proposed for the simulation of one-dimensional laminar flames with large kinetic mechanisms. An approximately factorized Jacobian is used as preconditioner to greatly reduce the computational cost associated with matrix operations. The constant, non-unity Lewis number assumption is introduced to reduce the computational cost and improve the convergence of the solver. The solver is applied to laminar flame speed calculations with kinetic mechanisms of varying sizes (up to thousands of species). Laminar flame speeds and species profiles are found to be in very good agreement with other codes. The computation times increase only linearly with the number of species. This is a significant improvement over traditional steady-state solvers for which the computational cost scales quadratically with the number of species. For the largest mechanism tested, the present solver is two orders of magnitude faster than commonly-used codes. The use of an approximate Jacobian does not significantly affect the domain of convergence, making the solver well suited for laminar flame speed sweeps with large kinetic mechanisms.