Effect of pressure on the transfer functions of premixed methane and propane swirl flames
AuthorsDi Sabatino, Francesco
Guiberti, Thibault F.
Roberts, William L.
Moeck, Jonas P.
KAUST DepartmentPhysical Sciences and Engineering (PSE) Division
Mechanical Engineering Program
Clean Combustion Research Center
KAUST Grant Number1975
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AbstractThis paper reports on the effect of pressure on the response of methane–air and propane–air swirl flames to acoustic excitation of the flow. These effects are analyzed on the basis of the flame transfer function (FTF) formalism, experimentally determined from velocity and global OH* chemiluminescence measurements at pressures up to 5 bar. In parallel, phase-locked images of OH* chemiluminescence are collected and analyzed in order to determine the associated flame dynamics. Flame transfer functions and visual flame dynamics at atmospheric pressure are found to be similar to previous studies with comparable experimental conditions. Regardless of pressure, propane flames exhibit a much larger FTF gain than methane flames. For both fuels, the effect of pressure primarily is to modify the gain response at the local maximum of the FTF, at a Strouhal number around 0.5 (176 Hz). For methane flames, this gain maximum increases monotonically with pressure, while for propane flames it increases from 1 to 3 bar and decreases from 3 to 5 bar. At this frequency and regardless of pressure, the flame motion is driven by flame vortex roll-up, suggesting that pressure affects the FTF by modifying the interaction of the flame with the vortex detached from the injector rim during a forcing period. The complex heat transfer, fluid dynamics, and combustion coupling in this configuration does not allow keeping the vortex properties constant when pressure is increased. However, the different trends of the FTF gain observed for methane and propane fuels with increasing pressure imply that intrinsic flame properties and fuel chemistry, and their variation with pressure, play an important role in controlling the response of these flames to acoustic forcing.
CitationDi Sabatino F, Guiberti TF, Boyette WR, Roberts WL, Moeck JP, et al. (2018) Effect of pressure on the transfer functions of premixed methane and propane swirl flames. Combustion and Flame 193: 272–282. Available: http://dx.doi.org/10.1016/j.combustflame.2018.03.011.
SponsorsThis work is funded by the Center of Competitive Funding from King Abdullah University of Science and Technology (Grant No. 1975).
JournalCombustion and Flame