Fuel and Equivalence Ratio Effects on Transfer Functions of Premixed Swirl Flames

Abstract

This paper reports on the effects of fuel and equivalence ratio on the response of lean premixed swirl flames to acoustic perturbations of the flow, at atmospheric pressure. The response is analyzed using flame transfer functions, which relate the relative heat release rate fluctuations from the flame to the relative velocity fluctuations of the incoming flow. Two fuels, propane and methane, and five equivalence ratios are considered. The ten flames investigated are selected to exhibit the local maximum of the transfer function gain around the same frequency, 176 Hz. The results show that changing fuel and equivalence ratio influences both

Influence of the Laminar Burning Velocity on the Transfer Functions of Premixed Methane and Propane Swirl Flames

“…Next, the dynamics of the flames and the unforced velocity fields are analyzed for different values of S L . At last, the parameters controlling the gain response at 336 Hz are discussed and compared with an analysis of the flame response at 176 Hz, which is detailed in another paper [31].…”

“…Since the propane flames feature a Lewis number different from unity (Le = 1.89), the unstretched laminar burning velocity, presented in Table 1, could be affected by the local curvature of the flame. However, it has been shown in [30,31] that for the range of forcing frequencies considered in this work, the non-unity Lewis number effects on the laminar burning velocity are negligible. Therefore, differential-diffusion effects are ignored for the remaining analysis and the local burning velocity will be considered as equal to the unstretched laminar burning velocity S L , presented in Table 1.…”

“…At this frequency, the gain of the FTF shows a nonmonotonic trend with increasing S L . A detailed description and discussion of the results obtained at 176 Hz can be found in [31]. In the present study, a brief summary of the main findings is given, in order to broaden the discussion conducted for 336 Hz.…”