Experimental and numerical study of a full-size direct-connect dual-inlet DRE with a fuel-rich metalized solid propellant
Ducted Rocket Engine (DRE) is an important air-breathing propulsion technology. Its characteristic configuration includes air inlets and afterburning chamber for higher combustion efficiency and better working performance. In this paper, experiments were performed using a fuel-rich metalized solid propellant with an on-ground direct-connect facility. Various sensors were adopted inside the dual-inlet DRE for measuring temperature, pressure and thrust at the air-fuel ratio of 15. Meanwhile, Coupled Multiphase Reacting Phenomena Simulator (CMRPS), an in-house computational solver was developed and validated using two-way coupled Computational Fluid Dynamics and Discrete Element Method (CFD-DEM). The multiphase reacting flow inside DRE was successfully simulated at the same experimental working condition. Numerical results of the temperature, pressure fields and thrusts have good agreements with the measured experimental data. Temperature contours inside DRE indicate strong coupling effects because of the motion and combustion of metal additives. The highest temperature exists symmetrically near the downwind areas of dual inlets because of the induced high oxygen concentration and the enhanced secondary combustion. Mass fraction contours of main reacting components reveal the chemical pathways. Initially, propellant decomposes and then various components are injected into the fluid domain. Ammonium Perchlorate (AP) and magnesium react the fastest near the burning surface, which leads to a steep temperature increase there from 1050 K to over 2200 K. Then C-H components react gradually with the left oxygen in the primary combustor, while aluminum particles need to absorb heat and have difficult ignition characteristics because of oxidation cap. Air is induced into DRE through dual inlets, which contributes to the secondary combustion of C-H components and aluminum particles in the afterburning chamber. Besides influencing the temperature field, metal particles have great effects on the velocity field because of inter-phase drag force. Therefore, the central velocity characteristics on nozzle exit have obvious decrease, while thrust is increased comparing to the primary single-phase result. Average combustion efficiency can be statistically calculated with numerous exhausted metal particles. Moreover, thermal protection is important for the use of fuel-rich metalized solid propellant. Much attention was paid to the ablation characteristics inside DRE, which is closely related with the distribution of burning particles. CMRPS is meaning to the understanding and designing of multiphase combustor for higher combustion efficiency, meanwhile novel materials and thermal protection strategies can be pertinently improved for better working performance.
Keywords: Experiment, CFD-DEM, Particle trajectory, Combustion efficiency, Working performance, Thermal protection,