Gas-Phase Ignition of Premixed Fuel by Catalytic Bodies in Stagnation Flow

Abstract

Abstract-In this paper the gas-phase ignition of a premixed fuel by catalytic surfaces of finite sizes is studied, using asymptotic methods. The flow selected for this analysis was the planar stagnation flow. The ignition is generated by a finite thickness plate, the lower surface of which is at a uniform high temperature. This study considers two principal cases: the slightly catalytic and the strong catalytic surfaces. In the first case, there are three important regimes: (1) Regime A-for a plate temperature much lower than the adiabatic flame temperature, the reactant consumption is not severe. In this regime it is much easier to ignite the gas-phase mixture than in the strong catalytic case for the same flow and plate parameters. (2) Regime B-here the reactant consumption is very important for plate temperatures close to the adiabatic flame temperature. The Damkohler number for ignition in the gas phase is of the same order of magnitude as for the strong catalytic case. (3) Regime C-here the reactant consumption in the gas-phase consumes all the fuel before it reaches the plate. Therefore, the type of the surface has no more influence on the gas-phase ignition. For the strong catalytic case there exists only regime B and regime C. The advantage of ctaalytic combustion, from a thermal point of view, is that for regime B the catalytic surface can efficiently stabilize flames generated in extremely lean mixtures, but does not alter the flammability limits of this mixture. The flammability limits cannot be altered by the type of surface used. In all cases analyzed, the influence of the thickness of the plate is studied.