Hydrogen addition effect on cellularization and intrinsic instability of ethyl acetate spherical expanding flame

Abstract

The cellularization and intrinsic instability of ethyl acetate (EA) spherical expanding flame with different proportions of hydrogen (4%, 8%, 12%) were studied through experiments and theoretical analysis. The high-speed schlieren imaging technique combined with the image processing method was used in the constant volume combustion chamber to quantify the development of flame surface cracks and saturation time, crack length, number of cellular units, and average cellular area. The results show that the evolution of flame cracks can be mainly classified into two periods. In the first period, several initial cracks are generated on the flame surface. In the second period, cracks rapidly expand while forming a large number of small cellular units, and the surface areas also increase rapidly. The increase in the proportion of hydrogen led to an increase in minor cellular cracks and a more moderate structural evolution of flame cells during the second period. Afterwards, the involved thermodynamic parameters, including the thermal expansion ratio, flame thickness, effective Lewis number, critical Peclet number, and perturbation logarithmic growth rate of unstable flames, were quantitatively analyzed. The results show that an increase in initial pressure significantly reduces the flame thickness, leading to more unstable flame. In contrast, the proportion of hydrogen has less impact on the involved thermodynamic parameters, while the equivalence ratio is the primary factor influencing instability parameters. Additionally, the study examined the flame's self-acceleration characteristics and found that increasing the proportion of hydrogen reduces the tendency for ethyl acetate self-acceleration.