Parameters Analysis of Non-linear Combustion Instability Based on the Pulsed Trigger T-burner Technique

Abstract

High-amplitude pressure oscillation in solid propellant rocket motors shows nonlinear effects including the mean chamber pressure shift, limiting amplitudes of the acoustic oscillation, and energy transfer among acoustic modes. Along with the obvious undesirable vibrations, these features lead to the most damaging impact of combustion instability on system reliability and structural integrity. However, the physical mechanisms behind these phenomena and their effect on the propellant combustion and the acoustic oscillation behavior have never been successfully established. Therefore, fully understanding of the nonlinear combustion instability is crucial in the design process. In this paper, the nonlinear combustion instability parameters are obtained based on the pulse trigger T-burner technique and the relationship between the propellant combustion and the nonlinear acoustic oscillation is analyzed. Some different formulas of the composite propellants are adopted during the 30 pulsed T-burner firings. The operating pressures of tests are set at 7MPa and 10.5MPa, and the acoustic 1st mode frequencies are set at about 170Hz and 255Hz. The results show that: the propellant combustion has significant influences on the mean pressure shift (DC Shift) and the initial limit amplitude. Under the same trigger pressure, the mean pressure shift and the initial limit amplitude are significantly higher than those without propellant combustions. The DC Shift increases about 13.7~39.3%, and the initial limit amplitude increases about 23.6~47.4% under the same trigger pressure. The propellants with different formulas lead to different combustion response characteristics, and subsequently the initial limit oscillation. The higher Rp of the propellant is, the higher oscillation amplitude will be in the T-burner. Furthermore, the mean pressure shift is proportional to the combustion response value of the propellant and the square of the acoustic pressure oscillation amplitude.