Combustion of 5-micron Aluminum Particles in High Temperature, High Pressure, Water-Vapor Environments

Abstract

An experimental investigation of the combustion times for nominally 5-µm aluminum particles in water vapor at high temperatures and p ressures is presented. The University of Illinois at Urbana-Champaign heterogeneous shock tube facility was used to independently vary the ambient temperature (>2300K), pressure (4-20atm) and composition of water vapor in argon diluent (20-100%) and to observe the combustion of Al particles behind a reflected shock. Burn times were calculated based upon light emission from bands of AlO, an aluminum combustion intermediate. Because the light signals with H 2O as an oxidizer showed longer burn times and more irregular peaks than those found when using O 2 or CO 2 as an oxidizer, different schemes for calculating b urn time based upon intensity cutoff and cumulative intensity thresholds were attempted. The 10-90% area threshold method of burn time was selected and used to report data. A parametric study of the conditions shows that burn time decreases with composition at a faster ra te than predicted by diffusion limited theory or the Beckstead correlation. The temperature dependence on burn time is negligible beyond 2500K. A burn time that increased with pressure was an unanticipated result. A correlation is presented for the burn time as a fun ction of these parameters.