Investigation of the Structures of Attached and Lifted Flames with Various Ignition Positions over a Triple Concentric Burner in the Hysteresis Regime

Abstract

This study focuses on the turbulent nonpremixed flame characteristics in a triple Concentric burner with the ignition positions "on the burner" (upstream position) and "above the burner" (downstream position). The flames were attached and lifted when the ignition positions were upstream and downstream, respectively. Numerical simulations were performed for cold flow, attached, and lifted flames. The calculated lift-off height and velocity profiles were in good agreement with the experimental results. In both the attached and lifted flame cases, the flame was situated along the stoichiometric mixture fraction line and in the region where the Damkohler number (Da) was > 1. The stoichiometric mixture fraction curve below the lifted frame was on the same line as the stoichiometric equivalence ratio curve of the cold jet. Furthermore, it was found that the two flames exist at the crossover point of the triple curves, which are comprised of the stoichiometric mixture fraction curves of two flames, the Da = 1 curves of the two flames, and the stoichiometric equivalence ratio curve of the cold jet. It was inferred that cold jet fields may dominantly affect the characteristics of a turbulent nonpremixed flame. That is, the ignition position it, the cold jet determines the bifurcation of the attached and lifted flames.