Thermal pyrolysis and combustion of HTPB-based solid fuels for hybrid rocket motor applications

M. J. Chiaverini, N. Serin, D. K. Johnson, Y. C. Lu, K. K. Kuol, G. A. Risha

Research output: Contribution to conferencePaperpeer-review

3 Scopus citations


A high-pressure, windowed, slab geometry hybrid motor analog was designed and utilized for conducting an experimental investigation on the combustion and pyrolysis behavior of Hydroxyl-terminated polybutadiene (HTPB) solid fuels burning with GOX. The lab-scale motor has operating conditions similar to those of sub-scale and full scale motors with respect to GOX mass flux and pressure. A real-time X-ray radiography system and an ultrasonic pulse-echo system were both used to obtain instantanous solid fuel regression rates at various axial locations. Fuel temperature measurements were made using an array of 25 μm fine-wire embedded thermocouples. The solid fuel regression rate was found to behave differently in each of three different regions: entrance regime near the head-end, laminar flow regime, and turbulent flow regime. The regression rates displayed a very strong dependence on axial location in the entrance region. In addition, a location of minimum regression rate was found to exist on the fuel slab and to move downstream with time. Gas-phase radiation was found to influence the regression rate at lower mass fluxes levels. A 20 weight percentage addition of ultra-fine aluminum (UFAL) powder to the HTPB fuel was found to increase the fuel mass flux by 70% over that of pure HTPB. Correlations were developed to relate the regression rate to operating conditions and port geometry in the laminar and turbulent regimes for pure HTPB and in the laminar regime for HTPB loaded with certain fractions of UFAL. Pyrolyzing fuel surface temperatures for pure HTPB were found to be between 930 and 1190 K, depending on operating conditions. The deduced thermal wave profiles were steeper (thinner thermal waves) under high mass flux conditions, indicating higher heat flux to the solid fuel surface. The HTPB activation energy was estimated at 11.5 kcal/mol, suggesting that the overall pyrolysis process is governed by formation and desorption of high molecular weight fragments from the fuel surface. The deduced regression rates and surface temperatures were found to compare reasonably well with those estimated by other researchers.

Original languageEnglish (US)
StatePublished - 1996
Event32nd Joint Propulsion Conference and Exhibit, 1996 - Lake Buena Vista, United States
Duration: Jul 1 1996Jul 3 1996


Other32nd Joint Propulsion Conference and Exhibit, 1996
Country/TerritoryUnited States
CityLake Buena Vista

All Science Journal Classification (ASJC) codes

  • Energy Engineering and Power Technology
  • Electrical and Electronic Engineering
  • Mechanical Engineering
  • Control and Systems Engineering
  • Aerospace Engineering


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