Measurements and a new correlation of methanol laminar flame speeds at temperatures up to 916 K and elevated pressures behind reflected shock waves

Abstract

A side-wall-imaging shock tube was utilized to measure the laminar flame speed of methanol in 21% O2/79% Ar (airgon) behind reflected shock waves. The flames, initiated via laser-induced spark ignition, were tracked through schlieren imaging, which allowed the extraction of unstretched methanol flame speeds using an area-averaged linear curvature model. Methanol/airgon flame speeds were measured at atmospheric pressure at four equivalence ratios (0.8, 1, 1.2, and 1.4) and at temperatures between 640 K and 916 K; elevated-pressure measurements at pressures up to 2.6 atm were performed at 750 K for three equivalence ratios (0.8, 1, and 1.2) and at pressures up to 2 atm at 820 K for the stoichiometric mixture. Four Kinetic models, NUIG 1.3, Aramco 3.0, FFCM-2, and Zhang 2017, were used to compare with the present measurements. The model-simulated flame speeds are observed to diverge at temperatures above 650 K, with the Zhang 2017 and NUIG 1.3 models showing the best agreement with experimental data. The Aramco 3.0 model is shown to consistently underpredict methanol laminar flame speeds at high temperatures and elevated pressures, whereas the FFCM-2 model shows overprediction at temperatures under 750 K, particularly at rich conditions. The methanol/airgon flame speed data were then mixture-scaled to obtain the equivalent methanol/air results, which trend closely with lower-temperature flame speed measurements reported in the literature. The first methanol/air laminar flame speed correlation validated at temperatures up to 916 K was constructed by fitting mixture-scaled methanol/air data and available literature values using a non-Arrhenius form.