Extinction of fuel and air stream diluted partially premixed flames for fire safety

This thesis presents an experimental and numerical investigation on the liftoff and extinction of fuel and air stream diluted partially premixed flames under normal and micro-gravity conditions. The results have applications to fire safety. Normal gravity experiments were conducted for laminar methane-air, ethylene-air, and acetylene-air coflow axisymmetric jet flames while microgravity experiments were conducted for methane-air coflow jet flames. The experiments were supplemented by detailed simulations of both coflow and counterflow flames. The effect of fuel and air stream dilution on flame liftoff height and extinction was determined to be a function of the equivalence ratio. Partially premixed flames were found to be more susceptible to fuel stream dilution while nonpremixed flames are more susceptible to air stream dilution. In a relative sense, C 2H4 and C2H2 flames are sequentially more difficult to extinguish than the corresponding CH4 flames. The fuel stream dilution of flames becomes progressively more effective than air stream dilution sequentially for CH4, C2H4 , and C2H2. Fuel and air stream diluted methane flames are more difficult to extinguish in mu-g than at 1-g; however, air stream diluted C2H4 and C2H2 flames are more difficult to extinguish in 1-g. Finally, a comparison of the relative effectiveness of the inert diluent CO2 is conducted with the chemically active halon-1301, CF3Br.