Study On Ignition And Combustion Characteristics Of Solid Fuel-rich Propellant Under Laser Irradiation

Solid fuel ramjet(SFRJ)has the characteristics of high specific impulse,long running time of engines,simple structure,high reliability,high safety and good economic performance,so it has broad application prospects The effects of oxygen content in the environment gas and pressure on ignition and combustion characteristics of aluminum-magnesium fuel-rich propellant were studied by experiment and numerical simulation in this paper.(1)Laser ignition experimental device was designed and built,and the ignition characteristics of aluminum-magnesium fuel-rich propellant under different pressure and oxygen content in environment gas were studied by that experimental device,the results show:the ignition gas phase reaction of solid propellant occurs in the dispersion region of the propellant pyrolysis product,the first flame is close to the propellant surface and the changing of oxygen content in environment gas has no effect on the propellant ignition delay time when the oxygen content in environment gas is less than that of the oxidizing gas of the propellant pyrolysis products;The ignition gas phase reaction of solid propellant occurs in the diffusion zone of the propellant pyrolysis products and the environment gas,the first flame is away from the propellant surface and the ignition delay time of solid propellant decreases when the oxygen content in environment gas is larger than that of the oxidizing gas in the propellant pyrolysis products,according to that,the physical diffusion model of propellant pyrolysis and environmental gas is proposed.(2)By using the pressure regulator valve,the combustion characteristics of aluminum-magnesium fuel-rich propellant under different pressure and oxygen content in environment gas were studied experimentally,the results show:the flame temperature of aluminum-magnesium fuel-rich propellant will decrease at the end of laser irradiation but the propellant can still continue to burn when pressure higher than 0.25MPa,the flame temperature gradually increased after 70ms;The flame temperature is in linearly positive proportion to the oxygen content and pressure.The burning rate of aluminum-magnesium fuel-rich propellant increases with the increase of pressure and oxygen content and the effect of them on burning rate is accord with B-number theory.By calculating the burning rate sensitivity coefficient ratio of pressure and oxygen content,it is found that the pressure is the main factor to affect the burning rate,however,as the pressure increases,the weakening effect of pressure on the flame "blow off effect" is no more sharp.This leads the influence of pressure on the burning rate to be reduced,relatively.The burning rate sensitivity coefficient ratio of pressure and oxygen content is decreased from?200 to?40 when pressure is increased from 0.1MPa to 1.5MPa.(3)The ignition and combustion process of propellant under different pressure and oxygen content in environment gas were simulated by the software Fluent with user defined function(UDF),the results show:the phenomena that the initial flame position of propellant ignited in different oxygen content is different can be reasonably explained by the physical diffusion model of propellant pyrolysis and environmental gas.The airflow of pyrolysis products deflect above the propellant during the process of moving forward,the maximum thickness of the diffusion zone appeared on the side of the airflow when press is 0.1 MPa;There is no obvious deflection of airflow and the maximum thickness of the diffusion zone appears above the propellant when press is 1MPa.The diffusion distance of the pyrolysis products decreases ass the pressure increases.The flame temperature distribution of computational domain axis shapes into saddle because the C4H6 in the center of flame can't burn out when the oxygen content in environment gas is 21%.