Dynamic characteristics of flame fronts in a turbulent premixed flame zone

Abstract

Instantaneous local flame front movements in the flame zone of a turbulent premixed burner flame have been examined using a micro-electrostatic probe with three sensors. Based on the measured values of the instantaneous inclined angle and velocity of the local flame front, frequency distributions at representative locations in the flame zone were derived. The results are shown to be consistent with those of the most probable direction and velocity measurements. Each frequency distribution is found to flatten as the measuring point moves from the unburned side of the flame zone to the burned side. A large number of velocity vectors of instantaneous, local flame front movements at representative locations are shown in vector distribution maps. Each vector was determined by using the values of the direction and velocity of the local flame front evaluated by analyzing three simultaneously recorded ion-current peaks. Local flame front movement is shown to change considerably from one instant to another. The scatter of the vector directions and magnitudes increases as the measuring point moves from the unburned side of the flame zone to the burned side. At the outermost point of the flame zone, the flame front moves downward at a certain instant, while at another instant the flame front velocity occasionally attains a value 3 times as large as the average value in the direction close to the average direction. The flame front movements at the top and side of the flame zone are shown to be almost the same, although the mean ion current and the flame zone width are different at these two locations.