Flame emission spectroscopy measurement and comprehensive characterization of various spray flames in a turbulent swirl burner

Abstract

In this study, a spray swirling combustion system focusing on five liquid fuels: methanol, ethanol, heptane, aviation kerosene, and sustainable aviation kerosene is built, and the combustion characteristics of spray swirling flames based on OH*, CH*, and C2* chemiluminescence characterization are further investigated. Subsequently, a quantitative model relating the chemiluminescence intensities of OH*, CH*, and C2* to the flame parameters is established, providing essential data for studying spray swirling flames. Results showed that the combustion efficiencies of the spray swirling flame for five liquid fuels positively correlate with the equivalence ratio and the airflow exit velocity. Yet the linearity between the chemiluminescence intensities of OH*, CH*, and C2* and the equivalence ratio is relatively low, and the efficacy of the intensity ratios OH*/CH*, OH*/C2*, and CH*/C2* in characterizing the equivalence ratio is limited. The correlation coefficients of the quadratic polynomial fitting between the chemiluminescence intensity ratio of OH*·C2*/CH* and the equivalence ratio exceed 0.98 under any airflow exit velocity condition, making it the optimal indicator for characterizing equivalence ratio in spray swirling flames. For the heat release rate, a power-law model based on the chemiluminescence intensity is proposed, demonstrating significantly higher effectiveness compared to the traditional linear models. The three-species power-law model utilizing the OH*, CH*, and C2* chemiluminescence intensities achieves the fitting accuracy exceeding 98% across the five fuels, providing a robust quantitative characterization for heat release rate in spray swirling flames. However, employing the chemiluminescence of single or two of the three radical species to determine heat release rates in liquid fuels lacks universality.