A study of the effect of thermal radiation on laminar flame propagation and ignition, 1981-1987

The effect of radiative heat transfer on the ignition and propagation of the laminar diffusion flame is considered analytically. The energy equation is generated based on a set of assumptions similar to those utilized by Spalding in his analysis of one-dimensional unsteady-state laminar flame propagation. The radiative absorption and emission terms are formulated in integral form based on the exact solution to the one-dimensional radiative transfer equation. The differential-integral equation is solved approximately based on the integral method.;Since the radiative heat transfer to and from the combustion zone depends strongly on the optical distance between the combustion zone and the hot and cold boundaries of a physical system, flame propagation in a radiative participating medium is intrinsically unsteady except in the optically thick and thin limits. From the numerical results, the initial optical thickness of the burnt and unburnt mixture are shown to have important effect on the flame propagation and ignition characters immediately after the two mixtures are brought into contact. The flame thickness is always increased due to the enhanced diffusion effect caused by radiation. Depending on the initial optical thickness, however, radiation can lead to either flame acceleration or flame extinction. The fuel consumption rate is shown to be an effective parameter correlating the importance of radiation effect.;The required minimum energy for a successful ignition is larger if radiative heat transfer is considered in the premixed combustion system. The amount of excess energy required is influenced primarily by the optical thickness of the initial pilot flame. This minimum energy for a successful ignition will be increased if radiative heat transfer is important in the premixed combustion system. The increment is dominant by the optical thickness of the pilot flame.