Investigation of Laminar Burning Velocities and Cellular Instability for Dimethyl Carbonate at Elevated Pressures

A spherical propagating flame experiment was performed to study the laminar burning velocities (LBVs), Markstein lengths, and onset of instability of flame fronts for dimethyl carbonate (DMC) at 373 K and initial pressures up to 8 atm, over the equivalence ratios of 0.7-1.5. An investigation of replacing synthetic air (21% O-2/79% N-2) with a mixture of 85.7% helium and 14.3% O-2 was carried out to present an in-depth analysis of instability for DMC spherical flames. The LBVs of both DMC/O-2/N-2 and DMC/O-2/He mixtures are observed to exhibit a downward trend with increasing pressures and reach their peak values in a slightly fuel-rich region near an equivalence ratio of 1.1. Measurements were subsequently compared to the simulations using three kinetic models available in the literature, revealing that the Alexandrino model yields better consistency with experimental LBVs. Sensitivity analysis was adopted to study the effect of pressure on DMC oxidation, in which sensitivity variation coefficients and normalized sensitivity variation coefficients were calculated to recognize the impressionable reactions to varying pressures. The results reveal that the increase in the initial pressure greatly facilitates some chain termination reactions, consequently causing competition to the dominated chain-branching reaction O-2 + H = O + OH, hence leading to the reduction in LBVs. Flame instability analysis indicates that the elevated initial pressures expand the instability of flame fronts and promote the formation of cellular structures. With the increase of the equivalence ratio, the flames would suffer stronger instability. While oxidizers with a diluent gas of helium can effectively suppress the cellular instability, it can be attributed to the higher diffusivity and lower specific heat of helium.

Automated summary

This study experimentally investigated the laminar burning velocities, Markstein lengths, and flame instability of DMC under different pressures. It was found that LBVs decrease with increasing pressure and reach peak values at an equivalence ratio of approximately 1.1. Sensitivity analysis revealed that increased pressure facilitates certain chain termination reactions, leading to a reduction in LBVs.