Thermal performance characteristics of a microcombustor for heating and propulsion

Abstract

Abstract Wall heat losses are a major impediment to ignition and flame stabilization in microcombustion. In this context, reactant preheating may improve flame stability in a microcombustor. This work is aimed at studying the flame response to changes in inlet temperature of an annular microcombustor burning hydrogen–air stoichiometric mixture. The proposed configuration uses a hollow inner tube filled with nitrogen to facilitate flame stabilization. A detailed axi-symmetric computational model for reactive flow was developed and tested for this purpose. The model predictions were used to evaluate suitability of the proposed design for gas turbine and other applications in terms of different indicators of thermal performance. The baseline data showed the operational feasibility of the proposed configuration. Reduction in the preheating zone length and improved ignition at the cross-stream sites combined to give an increasingly compact flame as inlet temperatures increased. However, the increased wall heat losses at higher inlet temperatures reduced the overall efficiency of microcombustor. This drawback offsets the gain obtained in the form of improved function of the inner tube due to higher inlet temperatures. As a result, the proposed configuration is suitable for gas turbine applications at low to medium values of the investigated temperature range subject to a critical assessment of increased heat losses and reduced heat reflux. The thermophotovoltaic and thermoelectric applications should be feasible at medium to high inlet temperatures.