Experimental and kinetic study on the laminar premixed cyclopentene/air flames

Laminar flame speeds of cyclopentene at different conditions (T = 450 K, p = 0.1 and 0.3 MPa and phi = 0.6-1.6) were measured in a constant volume combustion bomb. To better understand the effect of cyclic structure on combustion characteristics, laminar flame speeds of cyclopentene were compared with the other two C-5 alkenes (1-pentene and 2-methyl-2-butene, which are straight-chain molecule and branched-chain molecule, respectively). Results show that the laminar flame speed of cyclopentene is close to that of 2-methyl-2-butene, but lower than that of 1-pentene. Both hydrodynamic instability and thermal-diffusive instability were used to analyze the flame instability. Results show that 1-pentene flame suffers the strongest hydrodynamic instability, while cyclopentene flame suffers the strongest thermal-diffusive instability. A unified chemical kinetic model of C-5 alkenes was developed, which can well predict the ignition and combustion characteristics of three C-5 alkenes (1-pentene, 2-methyl-2-butene and cyclopentene) in different conditions. In addition, chemical kinetic analysis using the updated model shows that cyclopentene has a higher adiabatic combustion temperature than 1-pentene and 2-methyl-2-butene, which can increase the reactivity. However, cyclopentene has a strong ability to consume H and OH radicals and generate stabilized radicals, which in turn reduces the global reaction rate, thereby reducing the laminar flame speeds.