Sang Hee Won

Measurements of Extinction Limits of Methyl Decanoate Diffusion Flames and A Kinetic Study

In the present study, extinction strain rates of methyl decanoate/air diffusion flames have been measured as a function of fuel mole fraction in counterflow diffusion flames at an initial fuel temperature of 500 K and atmospheric pressure. A new high temperature detailed kinetic model is constructed for methyl decanoate oxidation based on the oxidation chemistries for methyl butanoate and n-heptane. The results show that the newly developed model reproduces experimental data from the literature, such as speciation profiles in a jetstirred reactor and diffusion flames. Model predictions also reproduce accurately the measured extinction strain rates of methyl decanoate diffusion flames. Analysis of these predictions shows that under diffusion flame conditions, the fuel is exclusively (>95%) consumed by metathesis reactions with H atoms. Formaldehyde, one of the major stable intermediates found in methyl ester oxidation, is produced via two different paths: one from the decomposition of methyl ester function group, and the other from small radicals in the core reaction zone. A comparative analysis of methyl butanoate and methyl decanoate extinction strain rate reveals that methyl decanoate exhibits a stronger resistance to extinction than methyl butanoate primarily as a result of its larger molar heating value. After accounting for the differences in the heating values and transport properties, both fuels exhibit the same extinction limit behavior, indicating the existence of an identical impact of ester kinetics present for both fuels.

Mechanisms of Kinetic Combustion Enhancement by O2(a1(delta)g)

The isolated enhancement effects of O2(a 1 Δg) on lifted flame propagation was investigated experimentally and numerically at reduced pressures. Through quantitative absorption measurements it was found that O2(a 1 Δg) was produced in excess of 5500 ppm and was isolated from all other plasma-produced species via NO injection before transport to the C2H4 lifted flame. Clear trends of increased flame propagation enhancement with increased O2(a 1 Δg) concentrations were found, with up to 3% enhancement observed. Numerical simulations with the current O2(a 1 Δg) kinetic mechanisms, containing only hydrogen species, showed significant trend deviations from the experimental results, indicating errors in the kinetics. The inclusion of new estimated temperature dependent rates of O2(a 1 Δg) collisional quenching by hydrocarbon species mitigated the deviation, but require validation. Flow reactor experiments with conditions mimicking the early stages of the flame showed that low temperature oxidation of C2H4 in the range of 583 K to 728 K mimicked the low temperature kinetic pathways of enhancement through NO sensitization with OH production. Therefore the inclusion of O2(a 1 Δg) quenching by hydrocarbon species, as well as low temperature chemistry is necessary for accurate modeling of the enhancement pathways by O2(a 1 Δg).