Non-monotonic behavior of flame instability of 1,3-butadiene/O2/He mixture up to 1.5 MPa

Non-monotonic behavior of Markstein lengths of 1,3-butadiene/O-2/He mixtures was studied in a constant pressure combustion chamber at initial temperature of 298 K, initial pressure of 0.5-1.5 MPa and equivalence ratios of 0.8-1.5. Markstein lengths of 1,3-butadiene/air mixtures were also measured at initial temperature of 298 K, initial pressure of 0.1-0.5 MPa for comparison. Non-monotonic behavior was also observed in both theoretical Markstein lengths and Markstein numbers of 1,3-butadiene/O-2/He mixtures, but was not observed in those of 1,3-butadiene/air mixtures. The effects of factors on non-monotonic behavior were studied. It is concluded that the rapid increase of Zel'dovich number in rich condition leads to the non-monotonic behavior of Markstein numbers of 1,3-butadiene/O-2/He mixtures, and further leads to the rapid increase of Markstein length. Both experimental and theoretical critical flame radius and Peclet number were obtained and showed similar non-monotonic phenomenon to Markstein lengths and Markstein numbers, respectively. It is indicated that the cellular structure will first appear near stoichiometric ratio, thus the laminar burning velocities of helium diluted mixtures under elevated pressure are easier to measure under both rich and lean conditions.