Flame-wall interaction of a forced laminar premixed propane flame: Flame dynamics and exhaust CO emissions

Abstract

This paper presents a systematic experimental study of the relative contributions of various near-wall flame dynamics to exhaust CO emissions. Exhaust carbon monoxide (CO) emissions and quenching distance measurements are reported for a laminar forced premixed propane flame undergoing flame-wall interaction. A vehicle-certification grade emissions bench was used to measure exhaust CO emissions at two points in the exhaust, one close to the flame and one far downstream of the flame. Flame chemiluminescence images were analysed to determine the quenching distance at 16 points in the forcing cycle. Four frequencies (f=5,20,35 and 60 Hz), three amplitudes (|u′/u¯|=0.02,0.05 and 0.15), and two cooling rates (Q˙c≈160 and 240 W), are compared to the unforced case. Higher forcing frequencies are observed to significantly change the flame shape during the forcing cycle. Increasing frequency is found to have a non-monotonic effect on the quenching distance, while increasing amplitude is found to decrease the mean quenching distance. Increasing the cooling rate is found to further decrease the mean quenching distance, which is in agreement with the literature. Exhaust CO measurements close to the flame reveal a small decrease at the higher cooling rate, while amplitude and frequency both had an order of magnitude less impact. Far downstream of the flame, exhaust CO measurements show that all cases converge to low CO concentrations. It is shown that a simple reactor network simulation reasonably predicts the exhaust CO emissions, far downstream of the flame.