A Study of Laser and Pressure-Driven Response Measurements for Solid Propellants at Low Pressure
Open Access
- Author:
- Kudva, Gautam Narendra
- Graduate Program:
- Mechanical Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- December 15, 2000
- Committee Members:
- Stefan Thynell, Committee Member
Thomas Litzinger, Committee Chair/Co-Chair
Vigor Yang, Committee Member
Michael Matthew Micci, Committee Member - Keywords:
- laser-driven
response measurements
solid propellants
pressure-driven - Abstract:
- This work was part of a larger program aimed at understanding and modeling propellant combustion and its interaction with changes in pressure and velocity in a typical rocket motor. A pressure driven combustion facility was developed and used to measure pressure-coupled amplitude and phase response during combustion of propellant samples at low pressure. Laser-driven experiments were also performed in a different chamber to measure propellant response at atmospheric pressure. A CO2 laser was used to ignite and sustain combustion during laser and pressure-driven combustion and also served as a source of oscillatory laser flux during laser-driven combustion. The laser did not play a direct role in the pressure-driven response measurements. The primary objective behind these laser-driven experiments was verification of the hypothesis in the literature that suggests the laser and pressure-driven propellant responses are analogous to each other. Advanced homogeneous propellants like HMX and heterogeneous AP composite propellants were tested under laser and pressure-driven experiments at pressures of 1, 2 and 3 atmosphere. Erikson at BYU has developed a model that predicts the behavior of HMX propellants under oscillatory combustion conditions and efforts also focused on comparisons between the experimental and numerical data. One-dimensional energy balance analyses in addition to steady-state temperature measurements were used to evaluate the effects of condensed-phase heat release and gas-phase heat feedback on the propellant response amplitudes. Steady-state species measurements were used to validate gas-phase chemical mechanisms for HMX and the AP/HTPB propellants. These validated mechanisms were then used in a one-dimensional premixed flame code to obtain the steady and unsteady components of the gas-phase heat feedback. An analytical model developed by Culick was used to perform parametric studies to evaluate the effects of gas-phase heat feedback and condensed-phase heat release on the magnitude of the response functions. An analytical model based on the work of Iribicu and Williams, and Roh, Apte and Yang was also used to obtain the response function as a function of gas-phase heat feedback and condensed-phase heat release and was compared to the experimentally measured response functions. Laser-driven response experiments on HMX showed that the response amplitude decreased with an increase in pressure. The unsteady component of the laser flux induces an unsteady component of the gas-phase heat feedback that is out of phase with the laser flux. The laser-driven experiments measured the response of the propellant to this net unsteady flux that is incident on the propellant surface. The increase in pressure increased the unsteady gas-phase heat feedback and hence decreased the net unsteady flux on the propellant surface and resulted in the lower response amplitudes. The pressure-driven response amplitudes increased with the increase in pressure because these experiments measured the propellant response to the unsteady gas-phase heat feedback that increased with pressure. Hence the laser and pressure-driven response experiments cannot be considered to be analogous for HMX. Comparisons with the numerical data of Erikson showed that the numerical model predicted a laser-driven response that is three times lower than the measured laser-driven response and predicts a pressure-driven response that is 50-70% lower than the measured pressure-driven response. Erikson believes this is due to poorly resolved condensed-phase kinetics and poor temperature sensitivity data. The analytical model of Culick also under-predicted the measured pressure-driven response profiles for HMX. Hence the analytical model of Iribicu and Williams was derived and provides reasonable agreement with the experimental values for pressure-driven response amplitude. This expression of Iribicu and Williams allowed for experimental inputs for the condensed-phase heat release and the gas-phase heat feedback. Clearly the difficulties in such experimental measurements reinforced the need for rigorous models that capture the appropriate physics. Comparison of the pressure and laser-driven response data with the theoretical transfer function of Son et al. showed that the transfer function severely under-predicted the experimental data at two and three atmospheres and slightly under-predicted the experimental data at one atmosphere. The simplifying assumptions to the ZN approach result in only limited use to this transfer function and hence it is ill advised to use this transfer function to predict pressure-driven response based on laser-driven response data. Laser and pressure-driven response amplitudes for the MURI 4 and 5 propellants decreased with an increase in pressure and laser flux due to the increase in the condensed-phase exothermicity and the decrease in the unsteady components of the net flux and gas-phase heat feedback incident on the propellant surface. The increase in pressure resulted in lower pressure-driven response amplitudes because the pressure change did not affect the gas-phase heat feedback but increased the exothermic heat release in the condensed-phase. The analytical model of Culick showed qualitative agreement in trends for the pressure-driven response function but continued to under-predict the experimentally measured values for the pressure-driven response function. The transfer function of Son et al. under-predicted the experimental data at both laser fluxes for the MURI 4 and 5 propellants. Clearly the limitations of the ZN approach results in limited use of this transfer function. The data clearly shows that the transfer function should not be used to obtain pressure-driven response data based on laser-driven experiments. Laser-driven response amplitudes for the AP/energetic propellants showed no change with the increase in laser flux, while the pressure-driven response amplitudes decreased with the increase in laser flux. The changes in mean laser flux had different effects on the laser and pressure-driven response amplitudes and suggest different driving mechanisms. Hence the laser and pressure-driven response functions should not be considered as analogous experiments. Laser-driven response amplitudes for the HTPE propellants increased with the increase in laser flux, while the pressure-driven response amplitudes decreased with the increase in laser flux. Once again the different effects of laser flux on the laser and pressure-driven response functions suggests different driving mechanisms and hence disproves the hypothesis that the two experiments are analogous to each other. Hence pressure-driven experiments coupled with detailed numerical models are essential towards obtaining predictive response functions for the advanced propellants.