Shock tube ignition delay time measurements for methyl propanoate and methyl acrylate: Influence of saturation on small methyl ester high-temperature reactivity

We report ignition delay time measurements for methyl propanoate (MP) and methyl acrylate (MA), carried out in a high-pressure shock tube. Experiments were performed behind reflected shock waves across a temperature range of 989-1 367 K, for fuel-air mixtures at equivalence ratios of phi = 0.5, 1.0, and 2.0, and nominal pressures of 1 and 4 MPa. Ignition delay times were found to decrease with increasing temperature, equivalence ratio, and pressure, and are well described with correlations involving Arrhenius temperature dependence and power-law dependence on equivalence ratio and pressure. Ignition delay times are compared with model predictions from literature kinetic models, with the models of Zhang et al (Energy & Fuels2014; 28(11): 7194-7202) and Bennadji et al (International Journal of Chemical Kinetics2011; 43(4): 204-218.) in good agreement with measured ignition delay times for MP and MA, respectively. Kinetic sensitivity analysis shows that the reactions most important for modeling ignition fall into two categories: initiation reactions (ie, decomposition and H-atom abstraction) and C-0-C(1)chemistry controlling the pool of small radicals. The unsaturated MA was observed to have lower reactivity than MP, due to its greater bond strengths for C & x2500;C and C & x2500;H bonds, resulting in slower rates for initiation reactions.