Numerical study on the effect of pressure on transient micro-combustion and heat release characteristics of AP/HTPB/Al composite propellant fuel

The effect of pressure on transient micro-combustion and heat release characteristics of AP/HTPB/Al composite propellant is investigated in the present study. Detailed combustion mechanism with 42 species and 136 reactions and segmented regression rate model are established and validated for the propellant fuel. The results show that temporal evolution of regression rate is not synchronous with temperature due to the heterogeneous properties of the burning surface. With combustion time increasing from t = 0.6 ms to t = 6.0 ms, the standard deviation of temperature of the burning surface increases by 65.08% while the standard deviation of regression rate decreases by 18.80%. Although raising pressure increases both the temperature and regression rate of the burning surface, the distribution uniformity of temperature and regression rate exhibits distinct response characteristics to pressure. With pressure increasing from 2 MPa to 10 MPa, the standard deviation of temperature of burning surface decreases by as much as 36.50% due to enhanced heat transfer to the burning surface. However, the standard deviation of regression rate increases by as much as 66.68% with pressure. Both the gas-phase temperature and solid-phase temperature increase and become more uniform with pressure. With progress of combustion, total heat transfer coefficient decreases slightly due to the reduced combustion heat release rate. Although the contribution of heat radiation increases significantly during the combustion process, heat convection is dominant heat transfer. With the increase of pressure, the combustion heat release rate increases significantly due to the enhanced oxidation reactions in diffusion flame. With consumption of the propellant, the combustion heat release rate decreases and squeezes to a smaller region. The experimental results of extinguished burnt surface show that AP particles become higher than the surface of HTPB binder as pressure increases. The non-uniformity of morphology of the burning surface of the AP/HTPB/Al composite propellant increases with pressure.