||In this study, the complete Navier-Stokes equations are used in the mathematical formulation and the flame combustion is modeled by a simplified single-step reaction for methane-air mixture to investigate the different parameters such as wall-temperature, inlet velocity, diverging angle, and distribution of flame behaviors.|
When wall-temperature is at 600K, the steady tulip-shaped flame exists in the low-velocity region, the oscillating flame in the mid-velocity region, and the slant-shaped flame, with length increasing with velocity, in the high-velocity region. The flame front will move toward the downstream when the velocity increases. When changing the wall-temperature from low to midrange, the steady flame shape is changes from mushroom to tulip and the only to oscillating flame in the high-temperature range. Due to the thermal coupling between the wall-temperature and flame, the location of flame front moves to the upstream when wall-temperature is increased. The diverging angle of the flow channel affects not only the mass flux but also the flow field. The oscillating flame behaviors are observed in small-angle channel and steady flame behaviors in the large angle (θ=5^°) channel.
In the research of oscillating flame, increasing inlet velocity makes the flame front moves to the downstream and makes the stretching flame longer. In the high-velocity region, the period of time becomes longer due to the flame extension. The increase of wall-temperature makes the flame front moves toward the upstream, makes the stretching flame shorter and the period of time becomes shorter with the increasing wall-temperature. For the angle effects of diverging channel, the stretching flame becomes shorter with the increase in angle with less effect on the location of flame front. In addition, the oscillating flame in the parallel channel is stronger and more irregular with a short period of time.