Ignition Probability of Turbulent Non-Premixed Swirling Flames in a Double-Swirl Burner

In this paper, the effect of swirl number on mixing structure and ignition probability in turbulent non-premixed natural gas/air flame has been investigated. The flames are visualized by a digital camera and inverted by Abel's transformation. Maps of ignition probability are generated by changing the spark position axially and radially while the flow field and mixing topology are established using numerical simulation. Three zones were defined based on the probability of successful ignition. The first one was the ineffective zone where the probability of a successful ignition was less than 20%. The second one was called the transition zone where the probability of a successful ignition was between 20% and 80%, and a successful ignition was highly dependent on the spark location. The third one was called the high-probability zone where the probability of a successful ignition was more than 80%. It was found that although the increment in swirl number improves the rate of mixing, it does not result in a better distribution of successful ignition probability. In high swirl numbers, the high-probability region is very small but at lower swirl numbers, the high-probability region is distributed at the burner exit, resulting IN better ignition characteristics.