A kinetic investigation on low-temperature ignition of propane with ozone addition in an RCM

To extend the temperature for propane ignition to a lower region (< 680 K), ozone (O 3 ) was used as an ignition promoter to investigate the low-temperature chemistry of propane. Ignition delay times for propane containing varying concentrations of O 3 (0, 100, and 1000 ppm) were measured at 25 bar, 654–882 K, and equivalence ratios of 0.5 and 1.0 in a rapid compression machine (RCM). Species profiles during propane ignition with varying O 3 concentrations were recorded using a fast sampling system combined with a gas chromatograph (GC). A kinetic model for propane ignition with O 3 was developed. O 3 shortened ignition delay times of propane significantly, and the NTC behavior was weakened. O atoms released from O 3 reacted with propane through hydrogen abstraction reactions, which led to the fast production of OH radicals. The following oxidation of fuel radicals generated additional OH radicals. Consequently, the inhibition caused by the slow chemistry of hydrogen peroxide (H 2 O 2 ) in the NTC region was weakened in the presence of O 3 . Experimental results with O 3 addition can provide extra constraints on the low-temperature chemistry of propane. Species profiles during propane ignition at 730 K with 1000 ppm O 3 addition showed the production of propanal (C 2 H 5 CHO), acetone (CH 3 COCH 3 ), and acetaldehyde (CH 3 CHO) was promoted significantly. Model analyses indicated that O 3 shifted the oxidation temperature of propane to a lower region, in which reactions of ROO radicals (NC 3 H 7 O 2 and IC 3 H 7 O 2 ) tend to generate RO radicals (NC 3 H 7 O and IC 3 H 7 O). The promotion of RO radicals led to the fast production of C 2 H 5 CHO, CH 3 COCH 3 , and CH 3 CHO. The corresponding species profile highlighted the reaction relevant to ROO and RO radicals (NC 3 H 7 O + O 2 = C 2 H 5 CHO + HO 2 and 2 IC 3 H 7 O 2 = 2 IC 3 H 7 O + O 2 ). Rate constants of these reactions were updated, which can potentially improve the performance of the core mechanism under lower temperatures and provide references for model development of larger hydrocarbons.