Burning Rate Numerical Simulation Of High-Energy Solid Propellant

To achieve the aims of long range and accurate attack of rocket/missile, energy improvement is always one of the main goals of weapon development. The energy of solid propellant is realeases by combustion, so there is a closed relationship between combustion characteristics of solid propellant, such as burning rate, pressure exponent, and performance of solid rocket motor. Continual improvement of combustion characteristics of solid propellant is the urgent need of rocket/missile weapons. However, the development of series new kind of propellant or improvement of propellant properties still mainly accord to the following steps: firstly, the determination of basic composition by energy calculation; secondly, selecting a certain or several compounds as combustion catalysts by experience to adjust the combustion characteristics; lastly, approaching the predetermined performance index by repeated correcting composition and changing combustion catalysts or that of combination. This practice will often cause the wasting of time, human, material resources and financial resources, and not always finally achieve the predetermined performance index. To change present situation, it should strengthen the research on the basic theory and combustion mechanism of solid propellant and grasp the relationship between the basic composition, combustion catalysts, and other components. If the combustion model of solid propellant can be successfully realized, it can be have more profound understanding of combustion phenomena and combustion regularity. Then, further optimizing the composition design, adjusting and controlling the combustion characteristics, and finally achieve the purpose of improvement of weapon performance. This research intends to study the combustion characteristics and combustion mechanism of the high-energy solid propellant, and proposes its combustion model based on the free radical theory to apply some technical support for the combustion characteristics adjustment.Firstly, by analyzing the combustion characteristics of nitramine/azide propellant, proposing the combustion model of RDX/AMMO-BAMO (80:20) based on the elementary chemical reactions of the gas phase. The model is a steady state, one-dimensional model. The calculated the burning rate, pressure exponent, the gas-phase heat feedback and the temperature are in reasonable agreement with experiment. The calculated results show that the inert gas N₂ decomposed from the copolymer AMMO-BAMO dilutes the concentration of reactants, which decrease the reaction rate of the elementary chemical reactions near the burning surface and the gas-phase heat feedback. So the addition of 20% copolymer AMMO-BAMO decreases the burning rate of RDX by 42%. Secondly, comparing the similarities and differences between the NEPE (Nitrate Ester Plasticized Polyether) propellant and composite modified double base (CMDB) propellant, such as the composition features, the flame structure, the combustion wave distribution and quenched surface, and proposing the combustion model of NEPE propellant based on the early free radical theory. The hypothesis of the thermal decomposition behavior of PEG, PET and GAP near the burning surface is proposed. Their chemical structure parameters are put forwarded, which broaden the original database content. The burning rate and pressure exponent formula of NEPE propellant are derived by introducing the correction factors to reflect the effect of content and particle size of AP, RDX, HMX and Al.Thirdly, the calculation program is compiled using the derived burning rate formula of NEPE propellant. The burning rates of PEG, PET and GAP system propellant are calculated by this program. The calculated results are in reasonable agreement with experiment, and most relative error are in 10% and all relative error are in 20%, which shows that the model and program are reasonable. At the same time, the calculated results show that AP can significantly improve the combustion characteristics: the content of AP increases, the burning rate increases and the pressure exponent decreases; the particle size of AP decreases, the burning rate increases and pressure exponent decreases. The effect of RDX content and particle size has a little effect on combustion characteristics of NEPE propellant comparing to AP. On the whole, when the particle size of RDX decreases, the burning rate decreases. For spherical aluminum, the particle size of aluminum decreases, the burning rate has the tendency of a saddle shaped change. When the particle size is less than 2μm, the pressure exponent significantly decreases. The burning rate increases with the increase of the content -ONO2 groups in nitrate esters.Lastly, the design ideal about combustion characteristics is proposed, that is, when the burning rate of binder system is equal to that of practical propellant, the erosive burning can greatly decreased and the combustion stability can be enhanced. At the same, the expressure exponent is discussed. The numerical simulation for catalytic combustion can be realized by improving the free radical function and introducing the catalyst characteristic parameters.