A ONE-DIMENSIONAL MODEL OF PILOTED IGNITION

In this article a model of piloted ignition is analyzed. The two-dimensional coupled solid and gas phase problem is simplified by assuming that the mass evolution rate from the combustible solid is a known function of time and by employing a plane rather than a point ignition source. Thus only a transient one-dimensional analysis of the gas phase is necessary. The equations are solved numerically using a fast scheme especially suitable for combustion problems. The pilot flame is modeled as a thin slab of gas that is periodically raised to the adiabatic flame temperature of the stoichiometric mixture. The effects of (1) ignition source location, (2) fuel mass evolution rate from the surface, and (3) surface temperature of the solid are investigated. An explanation is offered for the preignition flashes often observed experimentally. A rational criterion for positioning of the pilot flame is proposed. The minimum fuel flow rate, by itself, is found insufficient for predicting the onset of piloted ignition; heat losses to the surface play an important role. Also, the conditions at extinction of a steady diffusion flame are found to be very similar to those for piloted ignition. © 1990.