Quenching of Fuel-Rich Aluminum Powder-Air Mixtures in Microgravity Ignited by High-Energy Sparks Using an Electric Particulate Suspension (EPS)

摘要

The use of the Electric Particulate Suspension (EPS) method for evaluating quenching distance of fuel-rich aluminum-air powder mixtures has been tested in microgravity with high-energy sparks to 12.5 J (apparent energy). Experiments were conducted at NASA Glenn Research Center's (NGRC) 2.2 Second Drop Tower. The experimental design is reviewed. EPS in microgravity can generate high-powder concentrations (to 5 kg/m{sup}3 aluminum powder; equivalence ratio to 16) requiring less than one gram of powder per test cell. Criteria for achieving uniform cloud concentrations are discussed. The concept of "Excess Electric Field Strength" is introduced for microgravity. A specially designed 5-tier combustion rig provides 5 quenching data points during a drop. Test results (0g/1g) show scattered ignition data for fuel-rich powder mixtures while the lean flammability regime remains well defined. Anomalous (EPS) phenomena observed in microgravity are formations of "stringers" and "spider web-like" structures up to 2 cm in length that connect positive and negative electrodes. The formations are thought to be charged or polarized aluminum ash particles produced during the burnout stages of rich combustion.