Characterization of ozone-enhanced propane cool flames at sub-atmospheric pressures

Abstract

A recently developed experimental setup for the study of cool flames was employed to investigate low temperature combustion of propane. Cool flames were stabilized though ozone activation using a laminar flat flame Hencken burner at sub-atmospheric pressures. Propane cool flame stability was observed to be highly sensitive to pressure, and a pressure stability map is presented for a range of equivalence ratios (ϕ) from 0.17 to 1.0 in 0.17 increments and a range of reactant flow rates. Based on the stability map, a propane cool flame of ϕ = 0.17 at 17.3 kPa was chosen for further study. Flame lift-off height above the burner surface was measured and two operating regimes of burner-stabilized and freely propagating flames were observed. The intersection of these two regimes was used to estimate the cool flame propagation speed. Temperature measurements of the cool flame were taken and used in fixed-temperature numerical flame simulations. Additionally, flame temperatures and propagation speeds are presented for all equivalence ratios and pressures where stable, freely propagating flames were observed in the stability map. In order to enable non-fixed temperature, freely propagating cool flame simulations to be performed, reduction of a chemical kinetics model using the Directed Relation Graph method (DRG) in conjunction with reaction rate sensitivity analysis was performed. Experimentally determined propagation speed, temperature and species concentrations at partial equilibrium were compared to numerical simulations with reasonable agreement and results are discussed.