Investigation of Solid Oxidizer and Gaseous Fuel Combustion Performance Using an Elevated Pressure Counterflow Experiment and Reverse Hybrid Rocket Engine

Open Access
- Author:
- Johansson, Reed Halden
- Graduate Program:
- Aerospace Engineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- July 12, 2012
- Committee Members:
- Richard A Yetter, Thesis Advisor/Co-Advisor
Grant Alexander Risha, Thesis Advisor/Co-Advisor - Keywords:
- reverse
inverse
hybrid
rocket
counterflow
ammonium perchlorate
solid oxidizer - Abstract:
- Pressurized counterflow and static-fired motor studies were conducted to explore the possibility of a reverse hybrid system, having a solid oxidizer and gaseous fuel. Theoretical performance analysis indicates such a system may yield specific impulse and density specific impulse similar to composite solid propellants, yet with the added capability to throttle, shut down, and restart firings. Pressurized counterflow studies conducted using pressed ammonium perchlorate pellets and gaseous ethylene show three pressure dependent combustion regimes. At pressures below 1 MPa, ammonium perchlorate decomposition is controlled by heat transfer from the resulting fuel/oxidizer diffusion flame, exhibiting a weak dependence on flame strain rate and burning rates between 0.01 to 0.05 cm/s. As pressure increases, the monopropellant flame moves closer to the oxidizer surface until the pressure reaches the self-decomposition limit near 3 MPa, indicating that the monopropellant flame dominates the diffusion flame. Further increasing the pressure yields burning rates between 0.4 to 0.7 cm/s, which are consistent with the literature, and exhibit little strain rate dependence for the range of flow conditions tested. Similar studies conducted with methane suggest independence of fuel type. The pressurized counterflow apparatus was also utilized to examine the regression rate of hydroxyl-terminated polybutadiene with gaseous oxygen at varied pressures. The diffusion-controlled burning rates exhibited no pressure dependence, as expected, and agreed well with published regression rate data. Lab-scale static reverse hybrid rocket motor firings focused on the mid- to high-pressure combustion regime, examining ignition and system operating parameters. Results indicate that combustion is highly dependent on the initial pressure of the motor, producing a fast burn with initial pressures of 4.45 and 2.20 MPa, while behaving like a gas generator at a lower initial pressure of 1.14 MPa. Analysis also suggests that there is a minimum fuel flow requirement, below which the motor would not operate in the high pressure and burning rate regime.