Study of Utilizing Induction Heating to Modulate the Burning Rate of Solid Fuels and Propellants
Open Access
- Author:
- Walz, Kirstin
- Graduate Program:
- Mechanical Engineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- March 22, 2024
- Committee Members:
- Richard A Yetter, Thesis Advisor/Co-Advisor
Jacqueline Antonia O'Connor, Committee Member
Mary Frecker, Program Head/Chair - Keywords:
- Burning Rate
Induction Heating
Sold Fuel
Solid Propellant - Abstract:
- Solid rocket motors exhibit predetermined thrust profiles governed by propellant composition, burning surface geometry, and motor conditions. There is a desire to have throttleable solid rocket motors for trajectory optimization, multi-purpose capabilities, and improved energy management by controlling thrust and pressure. Currently employed methods modulate thrust output via mechanically operated pintle valves. However, these techniques are limited by control system accuracy and response time. Another means of modulating solid propellant burning rate is wired propellants, which offer custom or improved performance, but the mission profile's adaptability and heating uniformity could be improved. Some efforts have been made to investigate the application of an electric field to both gas phase flames and solid phase propellants/fuels to modulate burning rate. Results have found both increases and decreases, however, the mechanisms behind the changes in burning rate are not yet fully understood. Other active research initiatives investigate using microwave frequencies to enable burning rate modulation in propellant strands. However, microwave penetration depth is limited due to the high frequency and microwave coupling mechanism, thus limiting the heating uniformity at larger scales. This study investigates the use of induction heating (IH) to dynamically control solid propellant burning rate. Induction heaters utilize magnetic fields generated by a coil driven by a radio wave frequency (RF) alternating current. IH has two heating mechanisms relevant to this application: magnetic hysteresis heating and the Joule effect (eddy current heating). Both mechanisms are investigated by this study. Fuel and propellant samples with embedded magnetic nanoparticles (MNPs) were developed to observe the effects of magnetic hysteresis. Samples with embedded wires were used to look at eddy current heating. Thermal imaging was used to measure surface temperature of the fuel samples and raw MNP powders to characterize the relative magnetic hysteresis heating potential of a few select MNP susceptors. Results showed that the 30nm magnetite (Fe_3 O_4) particles provide the most relative heating via magnetic hysteresis , and 0.64mm diameter aluminum wires provide the most significant relative heating via the Joule effect. Further analysis of the magnetic hysteresis heating data shows that susceptor particle size can control the sample heating rate. The sample’s initially high heating rate slowed as temperature increased because the smaller particles reached a limit where their Néel relaxation time became less than the induction heater frequency, resulting in reduced heating efficiency. Propellant samples with embedded MNPs, heated via magnetic hysteresis, were found to exhibit a change in sample density due to the introduction of porosity thought to be caused by the dissociation of urethane bonds. Burning rate tests were performed on the propellant samples with embedded MNPs to observe dynamic changes in the burning rate when IH was applied. The results of burning rate testing found an average increase in burning rate of 131% through the heated section of the propellant sample. This result proves a significant change in burning rate can be achieved after ignition of a solid propellant grain has occurred. It is proposed that the large increase in burning rate is attributed to both the temperature sensitivity of the propellant and the increased burning surface area due to the induced porosity.