Combustion of Liquid Hydrocarbons in a High-speed Airstream

A theoretical formulation and experimental results of the high-speed mixing, ignition, and combustion characteristics of liquid fuels injected directly into a high-velocity airstream are presented. Experiments were performed in a direct connect constant area combustor supplied by a Mach 2 air stream at a static pressure level of 1 atmosphere and at total temperatures ranging from ambient (530°R) to approximately 3300°R. The fuel was liquid hexane and was injected laterally into the supersonic flow through piloted and nonpiloted injector configurations. It was found that autoignition and stable combustion occurs for air total temperatures above about 2600°R. Furthermore, the liquid fuel was effectively ignited and burned stably below this autoignition level by employing a small reacting pilot j et. Minimum pilot size and energy requirements were then established. It was found that the pilot mass flows needed for ignition and sustained combustion were small compared to the main fuel and air flow rates. Comparison with theory indicates combustion efficiencies up to 93% were obtained.