The Research On The Ignition Process Of Solid Fuel Ramjet

Based on related development work of the solid fuel ramjet extended-range projectile, the research on the ignition process of solid fuel ramjet was carried out by means of theoretical analysis, numerical simulation, and experiment investigation in this dissertation.The ignition processed of typical solid fuels (PMMA and aluminium-magnesium fuel-rich propellant) for solid fuel ramjet were examined in detail by use of a CO2laser ignition system. The results show that the ignition delay time of both fuels was decreased with the increase of ignition heat flux density. The effect of ignition heat flux density on ignition delay time decreased when the ignition heat flux density was high. In the ignition process of PMMA, which was typical gas-phase ignition process, PMMA thermal decomposition first, then the decomposition products combustion with air. For solid fuel ramjet use of PMMA as solid fuel, in order to ensure the reliability of ignition, based on a high heat flux density the ignition should extend it’s work time to complete the transition from the first ignition to the self-sustained combustion.Physical models and numerical calculation methods of the solid fuel ramjet ignition process were established according to flow, heat transfer, decomposition and combustion characteristics in the ignition process. On the basis of the CFD software FLUENT, the solid fuel decomposition plus transfer model was performed by using UDF. To verify the reliability of the calculation method, the numerical simulation of solid fuel auto-igniton in a sudden expansion combustor was carried out. The numerical results well conform to the experimental results.The numerical simulations of both solid fuel ramjet ring-ignition process and center-ignition process were carried out by using the calculation method which established previously. Influences on the ignition characteristics by parameters including the inlet air mass flow rate, the inlet air temperature, the ignition composition gas mass flow rate, the ignition composition gas temperature, and the solid fuel inner diameter were obtained. The research results show that the initial decomposition and fire of solid fuel was located near the igniter vent in the sudden expansion step recirculation zone in the ring-ignition process, followed by decomposition and combustion of the solid fuel gradually moving downstream. The initial decomposition and fire of solid fuel was located near the reflow attachment point in the center-ignition process, followed by decomposition and combustion of the solid fuel gradually moving both upsteam and downstream. In the ring-ignition process, the ignition delay time was decreased with the increase of the ignition composition gas mass flow rate and temperature or the decreased of the inlet air mass flow rate and temperature. In the center-ignition process, the ignition delay time was decreased with the decrease of the inlet air mass flow rate or the decreased of the solid fuel inner diameter. After the igniter work end, the air and MMA gas combustion supported the transition from the ignition state to the self-sustained combustion state in the solid fuel ramjet combustor.An experimental solid fuel ramjet which using central cone igniter and PMMA was designed, then the experimental study on the ignition and combustion characteristics of the solid ruel ramjet was carried out by using the direct connect experimental system. The experimental results provided the necessary basis for the numerical simulation of solid fuel ramjet center-ignition process. The research results show that the solid fuel mean regression rate was increased with the increase of the inlet air mass flow rate or the decrease of the solid fuel inner diameter. The experimental results of the pressure time curve well conform to the numerical results, therfore the established numerical method in this dissertation has high reliability. The numerical simulation results of the solid fuel mean regression rate variation with time and the solid fuel local regression variation with time well conform to the experimental results, however, there were some errors on specific values.The flow characteristics in the ignition process of solid fuel ramjet and the influences on the ignition characteristics by relational parameters were studied, as to provide a theoretical foundation and technical support for design and application of the solid fuel ramjet.