Atmospheric-pressure shock-tube measurements of high-temperature propane laminar flame speed across multiple equivalence ratios

Abstract

Laminar flame speeds of premixed propane in 21%O2-79% Ar (so-called ”airgon”) were experimentally measured in a shock tube at atmospheric pressure (1 atm±2%) for a range of equivalence ratios (0.5, 0.75, 1, and 1.2) and unburned-gas temperatures (644–1,044 K). Simultaneous side-wall schlieren and end-wall CH* emission imaging was utilized to track the propagation of outwardly expanding laminar flames initiated by laser-induced spark ignition behind reflected shock waves. The linear curvature model with an area-averaged formulation was used to extrapolate laminar flame speeds to zero-stretch. The high-temperature laminar flame speed results were compared with 1D simulations performed using two detailed kinetic models, NUIG 1.3 and Aramco 3.0, and two skeletal models, USC Mech II and San Diego 2016. The experimental results agree with the NUIG 1.3 model within 3.5%, while the predictions of the models disagree by up to 16%. Sensitivity analyses conducted using the models revealed six chemical reactions that strongly impact the prediction of laminar flame speed. In order for the present data to be compatible with practical combustion systems using air as the oxidizer, the propane/airgon measurements were scaled to obtain laminar flame speeds of propane/air using ratios calculated from 1D simulations. The scaled experimental measurements showed good agreement with literature propane/air results at 650 K. Empirical correlations of laminar flame speed as a function of unburned-gas temperature are then reported for the studied equivalence ratios.