Effect of Boundary Thermal Constraint on Planar Premixed-Flame/Wall Interaction

Abstract

The unsteady one-dimensional laminar isobaric propagation of a flame toward a wall, through a homogeneous fuel-lean premixture, characterized by large activation temperature, is examined under a Shvab-Zeldovich-type formulation, via numerical integration by the method of lines with spline interpolation. In particular, the effect of the boundary thermal constraint and of the Lewis-Semenov number, on the propagation in the immediate vicinity of a noncatalytic impervious planar wall parallel to the flame, is examined. Both an isothermal-wall constraint, for a series of values ranging from the initial cold temperature of the unburned premixture to the bulk-burned-gas temperature, and also an adiabatic-wall constraint, are considered. Persistence of unburned residual fuel, and occurrence of either large wall temperature or large wall heat transfer, are insights of interest in the context of current and proposed internal-combustion automotive engines. It is found that the largest gas-phase temperatures tend to be achieved at intermediate wall temperatures, for thermal diffusivity greater than mass diffusivity. In such cases, the release of chemical exothermicity, to enhance a “base enthalpy” of the premixture already augmented by significant heat transfer from the wall, leads to gas temperatures appreciably in excess of the bulk-gas adiabatic flame temperature. Inferences are drawn from the gas-phase aerothermochemistry concerning trade-offs in design requirements for ceramic-type, low-heat-transfer cylinder components.