Experiment on multiple fuel supplies to air breathing rocket combustors

An experimental study on multiple fuel supplies to cylindrical subsonic mode combustors of air breathing rockets was made for the purpose of reducing combustor length. The experiment consisted of two parts, one in which all the fuel was supplied through a rocket with multiple nozzles and the other in which a portion of the fuel was directly fed into a secondary combustor with the rest being supplied through a rocket with a single nozzle. The results are compared with each other and with those of a reference experiment in which a rocket with a single nozzle without fuel injection was used. In the case with multiple nozzles, mixing and combustion efficiencies were higher than those in the reference experiment for the same combustor length. They collapse to a single curve against the combustor length nondimensionalized by the rocket nozzle exit diameter, except for the combustion efficiencies for unstable combustion. Increase of the injection mass flow rate makes mixing and combustion efficiencies rise, but it soon becomes less effective beyond a certain limit. Combustion instability observed in the reference case for long combustors is suppressed in both cases.