Burning Velocity and Temperature Field Measurements of Aluminum-Air Flames at Elevated Pressure
Open Access
- Author:
- Foster, Garett
- Graduate Program:
- Mechanical Engineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- June 10, 2020
- Committee Members:
- Richard A Yetter, Thesis Advisor/Co-Advisor
Jacqueline Antonia O'Connor, Committee Member
Karen Ann Thole, Program Head/Chair - Keywords:
- Metal combustion
Aluminum combustion
Aluminum particles
Burning velocity
Pressurized combustion
Aluminum flame
Dust flame - Abstract:
- Aluminum is an energy-dense metal that reacts exothermically with oxygen, in addition to a range of other oxidizers, making it a potentially useful fuel for thermal propulsion and power applications. Fine aluminum dusts, with particle diameters on the order of micrometers, can be aerosolized and mixed with a gaseous oxidizer to produce dust flames from which heat can be extracted. The reactive properties of aluminum, combined with its natural abundance and long-term stability, make it a prospective replacement for fossil fuels in some energy or power systems. In order for the potential utility of aluminum-air dust flames to be assessed, understanding of the fundamental combustion behavior, such as the burning velocity and temperature, is necessary. Laminar aluminum-air dust flames have been previously studied at atmospheric pressure to measure the burning velocity and flame temperature. Typically, the effects of varying stoichiometry and particle size are reported. However, limited information exists on the effects of pressure and turbulence, which are often present in practical systems. This thesis will investigate aluminum-air dust flames with a focus on the effect of polydisperse particle size distributions, pressure, and turbulence intensity on the resulting burning velocity. Temperature fields of aluminum-air dust flames will also be investigated and reported for the first time. An experimental system was developed that allows metal dust flames to be observed within an optically-accessible high-pressure chamber. Using a high-speed camera, aluminum-air flames were imaged through two narrowband interference filters (700 nm and 900 nm). The images were used to calculate burning velocity along with a two-dimensional temperature field of the flame. All experiments were performed with fuel-rich aluminum-air mixtures. Three micron-scale aluminum powders with different size distributions of particles were tested at atmospheric pressure. The laminar burning velocity was found to increase with decreasing average particle size. A single size distribution of particles was tested at pressures ranging from atmospheric to ~105 psi. Laminar burning velocity was found to decrease with increasing pressure (P), with an approximate proportionality to P^-0.6 over the range of pressures tested. This was potentially due to the decrease in interparticle spacing and enhanced particle-particle interactions as pressure increased. A single particle size distribution was also tested at four different turbulence levels. The turbulence intensity at each level was measured using particle image velocimetry in a representative non-reacting flow. Burning velocity was found to increase with increasing turbulence intensity (TI), with an approximate proportionality to TI^1.0 over the range of conditions tested. Two-dimensional temperature fields were measured for two size distributions of particles and at elevated pressures up to ~105 psi using two-color ratio pyrometry. However, due to spectrally-dependent scattering/absorption and unknown emissive properties of the collected incandescent signal, only relative comparisons between the temperature measurements could be made.