A comparative laser absorption and gas chromatography study of low-temperature n-heptane oxidation intermediates

Abstract

A novel, multi-species, combined laser absorption/gas chromatography (GC) speciation diagnostic was used to quantify intermediate species present in the low-temperature oxidation of 1.0% n-heptane in 20.8% O2/Ar and 20.8% O2/0.21% CO2/Ar (equivalence ratio 0.53) at 760 K, 4.9 atm. Laser absorption techniques were used to measure initial fuel and time-resolved temperature, CO2, H2O, and C2H4. Sampled-gas GC analysis was used in conjunction with a variable-test-time shock tube facility to obtain quasi-time-resolved measurements of n-heptane, C2H4, CO, H2, C3H6, and CO2 in the same experiments. Measurements obtained using both techniques are compared to each other, and to initial results predicted by a detailed kinetic model using the experimentally measured pressure trace to constrain the model. Discrepancies between measured and predicted ignition delay times indicate the overestimation of three primary RO2 isomerization reaction rates. The three reaction rates were modified to improve agreement of modeled ignition delay times with the measurements. Final results produced using the modified mechanism are compared to the experimental results; the comparison shows close agreement between the two experimental measurement techniques, and measured species yields confirm the low-temperature reaction pathways that govern n-heptane decomposition and C2H4, CO, H2, and C3H6 production.