Pilot Ignition of Cold Supersonic Flows

Abstract

An experimental and theoretical study is reported of the ignition of a cold, ducted supersonic flow of premixed ethylene and air by means of a coaxial pilot flame. The boundary between conditions leading to ignition and conditions leading to quenching of the flame has been investigated experimentally, and compared with predictions from a computer model of the turbulent combustion process. Comparison has also been made with a simple ignition analysis based on a ratio of characteristic chemical and mixing length scales. Satisfactory agreement has been found between the experimental data and results of both theoretical studies. Nomenclature C p -specific heat D = pilot diameter D crit = minimum D to obtain ignition E = activation energy F = pre-exponential factor [Eq.(2)] / -distance to initiate reaction l m = minimum value of / L = potential core length m ox = oxidizer mass fraction w fu = fuel mass fraction P = static pressure R = gas constant T = static temperature T 0 = total temperature U = velocity X = axial distance from nozzle exit (/) -stoichiometric ratio, fuel-to-air p = mole fraction of combustible T. = ignition delay time i h -heat release time T = characteristic reaction time Subscripts m -minimum value 1 = conditions in cold combustible flow 2 = conditions in hot jet