Premixed flame propagation of CH_4 and C_3 H_8 in a narrow-gap disk burner using constant-volume processes at elevated-pressure

摘要

Premixed flame propagation within a narrow combustion space has been an important issue in combustionstudies. Recently, it was found that flame-induced instabilities are very sensitive to the lengthscaleof the combustion space. However, experimental results obtained at higher pressures have not beensufficient. In this study, the propagation characteristics of methane and propane premixed flames wereinvestigated using a new narrow-gap disk burner, of which the disk gap and the initial pressure couldbe varied precisely while the volume was kept constant. Quenching distances were measured during increaseof the initial pressure to 4 bar. Flame propagation characteristics were compared with variationof the disk gap, the equivalence ratio, and the initial pressure. Significant changes were found in thetrends of the flame propagation velocity and flame shape. Cellular flame structures were observed whenthe disk gap was slightly larger than the quenching distance regardless of the Lewis number. In contrast,smooth flames could form when the disk gap was sufficiently larger than the quenching distance. Theelevated pressure enhanced flame oscillation and cellular structures (if they could be generated) regardlessof Lewis number of mixtures. The relationship between the pressure and the flame propagation wasevaluated, and a mechanism for the flame instability is discussed herein.