A comparative numerical study of premixed and non-premixed ethylene flames

Detailed numerical simulations of premixed and non-premixed C2H4/air flames were conducted, using six available kinetic mechanisms. The results help a ssess differences between these mechanisms and are of interest to proposed hydrocarbon-fueled SCRAMJET concepts, in which C2H4 Can be expected to be a major component of the thermally cracked fuel. For premixed flames, lamina r flame speeds were calculated and compared with available experimental dat a. For non-premixed flames, ignition/extinction Z-curves were calculated fo r conditions of relevance to proposed SCRAMJET concepts. Results revealed a large variance in predictions of the kinetic mechanisms examined. Differen ces in laminar flame speeds as high as factors of 2.5 were found. For the c onditions investigated, computed ignition and extinction strain rates for n on-premixed flames differed by factors as high as 300 and 3, respectively. This indicates that while there are differences in high-temperature kinetic s that control flame propagation and extinction, discrepancies in low-tempe rature kinetics that control ignition can be even more significant. Sensiti vity- and species-consumption analyses indicate uncertainties in fuel kinet ics and, most importantly, on the oxidation Of C2H3 and the production of C H2CHO, whose kinetics are not well known and can crucially affect productio n of the important H radicals. These findings stress the need for experimen tal data in premixed and non-premixed configurations that can be used to as sess these phenomena and provide the basis for a comprehensive validation.