Droplet entrainment and its role in the combustion of HTPB/paraffin fuels

Abstract

Droplet entrainment offers high regression rate of HTPB/paraffin fuels, but also leads to more complicated mass and heat transfer mechanisms during combustion. The droplet entrainment of the fuels in a windowed two-dimensional (2D) slab burner were investigated by using a high-speed camera, and the convective heat transfer coefficient was modified. The results indicated that the entrained droplets could be easily generated below 1.29 MPa of combustion pressure (pc), which was dominant in the regression of fuels, whereas the regression rate decreased by approximately 0.9 mm when pc increased from 0.32 MPa to 1.29 MPa due to the negative correlation of droplet entrainment rate with pc. However, the regression at higher pc mainly depended on weak evaporation and thermal decomposition rather than droplet entrainment, which was insensitive to pc and decreased by only about 0.05 mm s−1 with the increase in pc from 1.85 MPa to 2.52 MPa. The carbonized layer could be easily formed on the burning surface at higher pc, which hindered the droplet entrainment. Additionally, the improvement of convective heat transfer coefficient with the presence of droplet entrainment was evaluated, and the blocking effect was weakened, especially under high oxidizer mass flux.