Comparative analysis of the stability and structure of premixed C3H8/O2/CO2 and C3H8/O2/N2 flames for clean flexible energy production

Abstract

The study compares the macrostructure and stabilization parameters of premixed oxy-propane (C3H8/O2/CO2) and oxygen-enriched air-propane (C3H8/O2/N2) flames at fixed inlet velocity of 5.2 m/s and under similar conditions of oxygen fraction (OF= 21%–70%) and equivalence ratio (ϕ=0.1−1.0) in a model dry-low-emissions (DLE) gas turbine combustor. The combustor stability maps were plotted within the ϕ-OF domain against background contours of constant adiabatic flame temperature (AFT), to quantify the blowout and flashback limits. It was found for both CO2- and N2-diluted flames that the blowout and flashback limits followed constant AFT contours on the stability maps. The blowout limit of both types of flames roughly followed the same AFT contour of about ∼1580 K, while the flashback limits followed the constant AFT contour of 2350 K. This implies that C3H8/O2/N2 flames blow out at leaner conditions compared to C3H8/O2/CO2 flames. The effect of diluent type on blowout limit diminishes at higher OF; above 55% both flames blow out at ϕ∼0.2. All flames of the same AFT exhibited considerably identical shapes despite having different OF and ϕ. Based on that, the design and operation of future oxy-fuel turbines is recommended to be AFT-based rather than OF or ϕ.