On the redox reactions between allyl radicals and NOx

NOx mitigation is a central focus of combustion technologies with increasingly stringent emission reg-ulations. 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 C3H5I 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 measured rate coefficients are close to the high-pressure limit. The measured values of the rate coefficients resulted in the following Arrhenius expressions (in unit of cm(3) /molecule/s): k(1) ( C3H5 + NO ) = 1 . 49 x 10(-10) exp (-6083. 6 K/T )( 1017 - 1252 K ) k(2)( C3H5 + N O-2) = 1 . 71 x 10(-10) exp (-3675. 7 K/T) ( 1062 - 1250 K ) To our knowledge, these are the first high-temperature measurements of allyl + NO x reactions. The re-ported 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. (c) 2020 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Automated summary

The study focused on measuring the absolute rate coefficients for the redox reaction between allyl radical (C3H5) and NOx, showing strong positive temperature dependence but no pressure dependence. This high-temperature measurement of allyl + NOx reactions provides valuable insights into the interaction of NOx with resonantly stabilized radicals and its effect on hydrocarbon fuels.