Autoignition of iso-octane at ultra-lean and lean conditions

Abstract

Ignition delay times (IDTs) of iso-octane/air mixture were measured in a high-pressure shock tube and a rapid compression machine at ultra-lean (Φ = 0.2) to lean (Φ = 0.4 – 0.6) equivalence ratios, pressures of 20 – 40 bar, and temperatures of 630 – 1250 K. Measured IDTs were longer at lower equivalence ratio, and the equivalence ratio effect was most prominent in the intermediate temperature range. IDTs were shorter at higher pressures and, likewise, the dependence on pressure was maximum at intermediate temperatures. Predictions of existing chemical kinetic models were compared with the experimental data. Notable differences were observed between the model predictions and the newly obtained IDT data at fuel-lean conditions. Sensitivity analyses were performed to identify key reactions affecting fuel reactivity at various temperature regimes. Rate coefficients of two sensitive reactions, IC4H8+IC4H9↔AC8H17 and AC8H17O2↔AC8H16OOH-C, were modified to improve model performance at intermediate and low temperatures for fuel-lean conditions.