Accelerating confined premixed flames using a transverse slot jet
Richter, Joseph P.
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An experimental study of the transient interaction of a premixed laminar methane-air flame propagating into a transverse fluidic obstacle is considered. The de agration-to-detonation transition (DDT) mechanism for use in pulse detonation engines (PDE) is the main but not only motivation for this study. When DDT is initiated through the use of solid obstacles, the system incurs a drag penalty and subsequent total pressure losses due to the physical obstacle impeding on the flow. This study utilizes a fluidic obstacle to generate flame acceleration without the subsequent penalties associated with form drag of a solid obstacle. The experimental setup was designed specifically for non-intrusive optical measurement techniques such as schlieren, CH* chemiluminescence and digital particle image velocimetry (DPIV). The channel utilizes a length to width aspect ratio of L/W = 6, and was chosen along with the fuel ( CH 4 ) to guarantee the impossibility of excessive overpressures associated with unanticipated detonations. The mixture is ignited in the center of the closed end of the channel, and the flame propagates towards the obstacle located at 3.1H. The medium emitted from the slot-jet orifice is the same methane-air mixture used to fill the channel and is released post ignition to allow an interaction with the laminar propagating flame. A comparison of this transverse fluidic slot jet obstacle is made to four different solid obstacle geometries at various blockage ratios (BR) and at stoichiometric and lean (&phis; = 0:88) equivalence ratios. The results of this study show that a transverse slot jet is capable of increasing heat release, flame surface area and subsequently flame speed compared to that of any tested solid obstacle with similar maximum flame deflection over an obstacle.