Investigation of the kinetics of OH∗ and CH∗ chemiluminescence in hydrocarbon oxidation behind reflected shock waves
The temporal variation of chemiluminescence emission from OH∗(A2Σ+) and CH∗(A2Δ) in reacting Ar-diluted H2/O2/CH4, C2H2/O2 and C2H2/N2O mixtures was studied in a shock tube for a wide temperature range at atmospheric pressures and various equivalence ratios. Time-resolved emission measurements were used to evaluate the relative importance of different reaction pathways. The main formation channel for OH∗ in hydrocarbon combustion was studied with CH4 as benchmark fuel. Three reaction pathways leading to CH∗ were studied with C2H2 as fuel. Based on well-validated groundstate chemistry models from literature, sub-mechanisms for OH∗ and CH∗ were developed. For the main OH∗-forming reaction CH + O2 = OH∗ + CO, a rate coefficient of k2 = (8.0 ± 2.6) × 1010 cm3 mol−1 s−1 was determined. For CH∗ formation, best agreement was achieved when incorporating reactions C2 + OH = CH∗ + CO (k5 = 2.0 × 1014 cm3 mol−1 s−1) and C2H + O = CH∗ + CO (k6 = 3.6 × 1012 exp(−10.9 kJmol−1/RT) cm3 mol−1 s−1) and neglecting the C2H + O2 = CH∗ + CO2 reaction.
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