On the Effects of Flow Swirl on Static Stability Limits and Flow/Flame Characteristics of Premixed Oxy-Methane Flames: An Experimental Study

ABSTRACTAn experimental study was performed to investigate the effects of flow swirl on flow/flame characteristics and stability of atmospheric premixed oxy-methane (CH4/O2/CO2) flames. The flames generated by two swirlers of 55° and 45° swirl angles were tested on a test stand for a dry low emission (DLE) model gas turbine combustor at constant inlet flow velocity of 5.2 m/s and over ranges of operating oxygen fraction (OF: 21% to 70% - by volume in the O2/CO2 mixture) and equivalence ratio (φ: 0.2 to 1.0). Combustor static stability limits (flashback and blow-out) were determined experimentally in the φ-OF domain to identify the operational ranges of the combustor while varying inlet flow swirl. To understand the mechanisms for flashback and blow-out, the lines representing the stability limits were displayed in the φ-OF domain against the contours of combustor power density (PD: MW/m3/atm), adiabatic flame temperature (AFT), and inlet flow Reynolds (Re). Comparison of flame macrostructure and measurements of local flame temperatures were performed for the two swirlers over ranges of φ, OF, and AFT to determine the effects of such operational parameters on flow/flame interactions and flame stability and to serve as a database for validating numerical models for such flames. The results show that, for both swirlers, the flames blow-out at a very similar AFT of ~1600 K indicating the dominant role of AFT in controlling premixed oxy-flame stability near the blow-out limit. Compared to the same combustor with a 55° swirler, the 45° swirler has a wider stable combustion zone. Comparing the flames of the same AFT, at fixed inlet flow velocity, shows almost identical flame macrostructure whatever the operating inlet flow swirl, OF and φ.KEYWORDS: Experimental combustionflow swirlflow/flame interactionsstatic stability limitsgas turbinesoxy-fuel combustion Nomenclature m˙=Mass flow rate [kg/s]FS=Flame speedLPM=lean premixedM=Molecular weight [kg/kmol]OF=Oxygen fraction (volumetric fraction of O2 in the O2/CO2 mixture)p=Combustor pressure [kPa]PD=Combustor power density [MW/m3/bar]Ru=Universal gas constant [kJ/kmol/K]Re=Throat Reynolds numberT=Gas absolute temperature [K]AFT=Adiabatic flame temperature [K]v=Bulk throat velocity [m/s]va=Axial component of bulk throat velocity [m/s]yi=Mole fraction of species iHC=Enthalpy of combustion [55.5 MJ/kg]Z=Axial distance above burner throat [cm]φ=Equivalence ratioρ=Density [kg/m3]μ=Dynamic viscosity [kg/m/s]mix=Reactant mixture (CH4+O2+CO2)i=Each mixture constituentAcknowledgementsThe authors like to acknowledge the backing received from King Fahd University of Petroleum and Minerals (KFUPM) through the KFUPM Consortium for Hydrogen Future on project No. H2FC2309.Disclosure statementNo potential conflict of interest was reported by the author(s).