Solid-fuel regression during ignition transient in a ramjet

Abstract

The transient regression and ignition of a solid fueld in a hot-oxidizing flow in a simulated combustor of a solid-fuel ramjet (SFRJ) were experimentally investigated. The local regression of solid fuel was measured at various intervals before ignition, and the controlled variables of the experiments were the inlet flow velocity, gas temperature, oxygen content, and step height. The maximum regression was located at 5.0–5.5 step heights from the entrance. The results of regression tests indicate that the influence of heat transfer was more important than the flow structure of the separated-reattaching flow. The regression rate increased with increasing the flow temperature and mass flow rate but decreased with increasing step height. The oxygen content had no significant influence on the regression before ignition. The transport phenomena in the combustor before ignition were closely related to the ignition mechanisms, which were diffusion control and chemical kinetics control. Diffusion control applied in the region of oxygen concentration greater than 20%, and the ignition delay decreased as pyrolyzed fuel vapor increased during the preignition period. Chemical kinetics control applied in the region of oxygen concentration less than, 15%, and the flow feature of flame stabilization was more important than pyrolysis for decreasing the ignition delay.