MICROWAVE PLASMA TORCH FOR ALUMINUM COMBUSTION

Open Access
Author:
Vamos, Michael Anthony
Graduate Program:
Mechanical Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
June 25, 2018
Committee Members:
  • Richard A Yetter, Thesis Advisor
  • Stefan Thynell, Committee Member
Keywords:
  • aluminum
  • combustion
  • plasma
  • torch
  • ignition
  • microwave
  • metal combustion
  • plasma assisted combustion
  • igniter
  • coaxial
  • spectroscopy
  • temperature fitting
  • spectrometer calibration
  • air
  • steam
  • carbon dioxide
Abstract:
Aluminum particles can be used as a fuel source in combustion systems. Breaching the protective oxide shell is critical in the initiation of the particle’s combustion, since the aluminum center cannot react until the shell is cracked or vaporized. Microwave plasma torches have been shown to be effective at igniting various fuels, including aluminum. This work investigates workable conditions of a coaxial microwave plasma torch for igniting aluminum powder. The plasma filament and aluminum particle interaction were also investigated. An argon plasma was formed in a coaxial torch and aluminum particles were passed through the filaments without any oxidizer. Through the use of spectroscopy, aluminum and aluminum oxide spectral peaks were observed. The post-plasma particles were collected and observed using a scanning electron microscope, showing that many particles were fused together. A plasma temperature fitting was performed with Specair showing an approximate temperature between 2500–3400 K. Combustion tests were performed using air, steam, and carbon dioxide as oxidizers. Combustion was achieved with all three oxidizers. The aluminum–air flame produced a stable and anchored flame. Aluminum–steam also produced a favorable anchored flame; however, it was not repeatable. Aluminum–carbon dioxide reacted with a small flame. Further tests with carbon dioxide still need to be performed. The aluminum–air flame was characterized over several equivalence ratios. The flame was anchored at the injector tip for lean and near stoichiometric conditions. Fuel-rich experiments still burned; however, the flame was thinner at the injector tip. For the lean and near stoichiometric conditions, the microwave power was able to be turned off after combustion began. iv The most stable configuration for the coaxial microwave plasma torch for igniting aluminum was: Equivalence ratio of 0.9 , annulus velocity of 8.8 m/s (10° swirl), core flow velocity of 1.0 m/s, and 200 W of microwave power with air in the outer flow and argon and aluminum powder in the core flow.