On the Redox Reactions between Allyl Radicals and NOx
NOx mitigation is a central focus of combustion technologies with increasingly stringent emission regulations. NOx can also enhance the autoignition of hydrocarbon fuels and can promote soot oxidation. The reaction between allyl radical (C3H5) and NOx plays an important role in the oxidation kinetics of propene. In this work, we measured the absolute rate coefficients for the redox reaction between C3H5 and NOx over the temperature range of 1000 – 1252 K and pressure range of 1.5 – 5.0 bar using a shock tube and UV laser absorption technique. We produced C3H5 by shock heating of C3H3I behind reflected shock waves. Using a Ti:Sapphire laser system with frequency quadrupling, we monitored the kinetics of C3H5 at 220 nm. Unlike low-temperature chemistry, the two target reactions, C3H5 + NO products (R1) and C3H5 + NO2 products (R2), exhibited a strong positive temperature dependence for this radical-radical type reaction. However, these reactions did not show any pressure dependence over the pressure range of 1.5 – 5.0 bar, indicating that the measure rate coefficients are close to the high-pressure limit. To our knowledge, these are the first high-temperature measurements of allyl + NOx reactions and our reported data will be highly useful in understanding the interaction of NOx with resonantly stabilized radicals as well as the mutual sensitization effect of NOx on hydrocarbon fuels.
Dapeng Liu is a Ph.D. candidate in the mechanical engineering program at KAUST. He is supervised by Professor Aamir Farooq. Before joining KAUST, he received his bachelor’s degree from Xi’an JiaoTong University (XJTU), China. His background in laser diagnostics, fuel kinetics, and shock tubes fuels his passion for revealing the kinetics of combustion such as soot formation and fuel oxidation. His PhD thesis work is focused on studying the rate constants of elementary reactions.