Numerical and Chemical Kinetic Analyses on the Formation of CO and CO2 for C1-C4 Hydrocarbon Alkanes in a Hot Co-Flow under MILD Combustion

In this present study, computational fluid dynamics and chemical kinetic analysis are conducted to explore the formation of CO and CO2 for a fuel jet comprising C1-C4 hydrocarbon alkanes in a hot co-flow burner under a moderate or intense low-oxygen dilution (MILD) combustion environment. The fuel jet comprises three cases of fuel mixture (case 1: CH4 + H2, case 2: C3H8 + H2, and case 3: C4H10 + H2) having constant mixture density and operating under a fixed jet Reynolds number. The combustion and emission characteristics are analyzed in terms of radial profiles of temperature and mass fraction of OH, CH2O, HCO, CO, CO2, and C2H2 in the MILD combustion region. The formations of CO and CO2 are examined with the help of reacting flow analysis using the computational fluid dynamics (CFD) tool. The formation of CO is reported as maximum for case 3 and minimum for case 1. However, the reverse trend is observed in the case of CO2 formation. The reacting flow analysis from the CFD work suggests that the reaction C2H2 + O = CH2 + CO strongly influences CO formation in all three fuel mixtures cases. In the current study, acetylene is found to be the primary species that affects the CO formation in the adopted fuel mixtures and is mainly responsible for the increased CO concentration in case 3. Likewise, the formation of CO2 is majorly influenced by the reaction CO + OH = CO2 + H. The reacting flow analysis is assisted with the help of a zero-dimensional perfectly stirred reactor (PSR) model to elucidate the underlying chemistry and explore the significant reaction pathways influencing the formation of CO and CO2. The ethylene route in the reaction pathway substantially plays a vital role in the CO formation in all three fuel mixtures.