AN EXPERIMENTAL STUDY ON UNSTEADINESS EFFECTS ON STRAINED NON-PREMIXED LAMINAR FLAMES

摘要

An experimental study was conducted on the effect of unsteadiness on strained, non-premixed, laminar flames in a counterflow configuration. Sinusoidal oscillations of the burner exit velocities were imposed by independently controlling the amplitudes and frequencies. The flame response was recorded by monitoring the oscillation amplitude of the luminous zone position at various amplitudes, frequencies, strain rates and fuel concentrations in the fuel stream. Experimental results showed that the flame responds to the external oscillations in different manners at different frequencies. By scaling the flame amplitude response with the Stokes' parameter that has been proposed in previous theoretical studies, all data were found to collapse into a single curve which validated the argument regarding analogy to Stokes' second problem. The extinction behavior under the presence of unsteadiness was also assessed. It was found that extinction response of flames in presence of external oscillations strongly depends on the frequency and the fuel concentration in the fuel stream. Flames at higher frequencies were experimentally found to resistant to higher strain rate amplitudes. These experimental findings do support past theoretical predictions.