Experimental and numerical study on combustion characteristics of super lean H2–O2 premixed laminar flame in argon atmosphere

Abstract

This paper presents an experimental and numerical research on super lean premixed H2–O2 flames under argon atmosphere in a combustion bomb with constant volume, and applied CHEMKIN to perform simulation for the flames. The high-speed schlieren photography is employed to record the development process of expanding spherical flame, and laminar burning velocities of super lean premixed H2–O2–Ar flames with different back pressures under argon atmosphere are calculated, and the influence of equivalence ratio and initial pressure on flame instability is analyzed, and the mass burning fluxes are calculated by simulation and flame structure and rate of elementary reactions is analyzed. The results show that, with equivalence ratio decrease, laminar flame velocity and mass burning flux will decline; with initial pressure increase, laminar flame speed will decline and mass burning flux will increase. For flame stability, when initial pressure rises, the hydrodynamic instability on hydrogen flame surface is enhanced, more easily resulting in cellular instability. As pressure rises, Lewis number and density ratio under each pressure will approximate to constant values, therefore, flame thickness is the main factor influencing flame instability when initial pressure rises. When equivalence ratio decreases, unequal diffusion instability often occurs easily under leaner conditions during flame development. According to simulation results, the laminar flame velocity is the result of interaction between the chain branching reaction and the chain termination reaction and the changes of equivalence ratio will affect above two reactions. For flame structure, the results show that when equivalence ratio is small, chemical reaction velocity of hydrogen gas burning will decline and reaction zone will enlarge, besides, H and OH concentration will also decline. As equivalence ratio decreases, the maximum H mole fraction constantly declines, which is consistent with the changing trend of laminar flame velocity with equivalence ratio.