Research of Combustion Control in Dual-Mode Ramjet Combustor with Staged Fuel Injection

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Supersonic flow with heat addition and combustion in rectangular ducts with diverging section, which are realistic configuration for the combustor of dual-mode ramjet engines, was investigated experimentally and numerically. Laser measurement methods of velocity and concentration were introduced for non-intrusive diagnostics of the flowfields with large separated regions.In the experimental study, one or two H2/N2 plasma torches were attached to the duct for heat addition to the supersonic airstream by electrical discharge and combustion of hydrogen in the feedstock of the torch, and formation of pseudo-shock wave and transition of combustion mode were observed. It was found that the divergence of the duct considerably suppress the formation of pseudo-shock waves and the transition of combustion mode. Results of experiments with various diverging angles indicated that the additional heat required to produce the pseudo-shock wave in the diverging duct could be estimated by the quasi-one … More dimensional theory. When the pseudo-shock wave was produced by the plasma torch in the constant area duct, another plasma torch in the diverging duct connected to the straight duct required certain amount of heat addition to affect the upstream section. From this result, it was shown that the staged fuel injection in the straight and diverging ducts could deliver more thrust than the single injection of the same total amount of fuel.In the numerical study, detailed features of the flowfield, such as the upstream propagation of the pseudo-shock wave front led by separation of thick boundary layer at the corner of the rectangular duct, and significant asymmetric separation in the diverging duct, were obtained. Numerical results validated the quasi-one dimensional theoretical evaluation of the heat addition required to compensate the influence of duct diverging.Using the particle image velocimetry, we obtained averaged three-dimensional velocity distributions in the flow up to 550m/s with shock waves and vortices. By the acetone planar laser induced fluorescence method, qualitative distribution of injectant in the whole flow field as well as the Mach number distribution near the injection port were obtained. These measurement techniques are applicable to the flow with the pseudo-shock wave and fuel injection. Less