T. Kravchik et E. Sher, NUMERICAL MODELING OF SPARK-IGNITION AND FLAME INITIATION IN A QUIESCENT METHANE-AIR MIXTURE, Combustion and flame, 99(3-4), 1994, pp. 635-643
The initiation of a spark kernel and the subsequent propagation of a s
elf-sustained flame in an internal combustion engine have been investi
gated numerically. A theoretical model which employs a two-dimensional
cylindrical coordinate system and assumes axial symmetry has been dev
eloped. It considers the various physical and chemical phenomena assoc
iated with the ignition process and employs a detailed chemical reacti
on scheme for a methane-air mixture which contains 29 chemical species
and 97 reaction steps. The thermodynamics and transport properties of
the plasma at high temperatures are evaluated by a statistical thermo
dynamics approach, while assuming local thermodynamic equilibrium. Usi
ng the PHOENICS and the CHEMKIN codes, the appropriate conservation eq
uations are solved in the domain of solution. It was concluded that th
e kernel growth can be described as a two-step process. In the early s
hort stage (1-5 mu s) the mass and energy transfer processes are very
much dominated by the pressure wave and the violently expanding plasma
kernel, while the contribution of the chemical reactions is negligibl
e. This stage is followed by a much longer period in which diffusion a
nd thermal conduction control mass and energy transfer as the flame be
comes gradually self-sustained. Owing to the heat release by chemical
reactions, the expansion of the combustible mixture is accelerated at
the beginning of the diffusive stage.