Secondary air injection in miniature liquid fuel film combustors

Previous investigations on fuel film combustors have shown the capability to burn liquid fuel in a minitaurized system, but challenges remain with respect to reaching a higher miniaturization level coupled with fully burning the fuel inside the combustion chamber. In order to achieve higher performance, this paper explores the idea of secondary air injection applied to a one centimeter diameter fuel film burner operating at ambient pressure oil liquid heptane. Ail investigation of operating limits was performed to map the stability and instability regions in the operating plane of air flow-fuel flow. The combustion and flame confinement was studied by varying the overall equivalence ratio, the length of the chamber and the distribution of the air flow into tangential air injectors. Visualization of the flow in cold and hot conditions were accomplished respectively with laser sheet and schlieren techniques accompanied by relative pressure measurements inside the combustion chamber in cold flow and by a comparison with CFD using a three-dimensional turbulent nonreacting model. An external wall temperature analysis provided an estimate of the heat loss and predicted the vaporization point of the fuel film. These properties affect the burning efficiency through the available residence time and the fuel/air mixing behavior. (C) 2009 The Combustion Institute. Published by Elsevier Inc. All rights reserved.