Ignition and combustion of aluminum particles in shocked H2O/O2/Ar and CO2/O2/Ar mixtures

Small aluminum particles (5-10 microns) are ignited in atmospheres consisting of Ar and varying amounts of H2O, CO2, and O2 at the endwall of a shock tube to study the burning characteristics in various combinations of these oxidizers. A reflected shock is used to obtain pressures of about 8.5 atm and temperatures of about 2600 K. Visible wavelength emission spectra are recorded by using a spectrometer coupled to a streak camera, and two photodetectors record intensity vs. time at AlO emission wavelengths of 486 and 514 nm. The streak camera allows recording of multiple time-resolved spectra at rates of 100 micro-s per spectrum. Aluminum particles ignited in mixtures of CO2/O2/Ar exhibited a burn time of about one half that of an atmosphere containing only a mixture of O2/Ar, holding the argon constant at 40 percent. In addition, as CO2 was substituted for O2 in successive experiments, a nonlinear relationship, as a function of the gas composition, was observed for ignition delay time and burn time. Within mixtures of HeO/O2/Ar, two distinct burning stages are visible for the combusting aluminum particles. (Author)