Convection Effects on the Endothermic Gasification and Piloted Ignition of a Radiatively Heated Combustible Solid

Abstract

A study is presented on the effect of convective conditions on the endothermic gasification and subsequent ignition of a slab of solid material heated by a radiant flux. A simple solid-phase thermal model is numerically integrated to approximately reproduce results of a previous experimental study of piloted ignition. The model is formulated in terms of the transient energy equation including endothermic Arrhenius-type pyrolysis and Beer-law in-depth absorption of the radiant flux. Temperature evolution curves are obtained for different values of the heat flux and convective coefficient, and are shown to accurately predict experimental surface temperature measurements prior to ignition. Material gasification rates are calculated and used in conjunction with the experimental ignition results to show that the piloted ignition delay closely corresponds to the time required by the solid to reach a critical value of the gasification rate. The critical gasification rate is nearly constant and independent of the heat flux for given convective conditions, and increases linearly with the convective coefficient. It is shown that the graphs of piloted ignition delay vs. heat flux may be accurately determined from this critical gasification criterion. Finally, a non-dimensional parameter that represents the relative amount of gasified fuel transported by the oxidizer stream is presented as a suitable measure of the flammability of the material.

Keywords:

• Solid Fuel Ignition
• Piloted Ignition
• Pyrolysis
• Flammability

Additional information

Notes on contributors

A.C. FERNANDEZ-PELLO

e-mail: [email protected]