Nitric oxide produced during combustion will be present in vitiated air used in many devices with exhaust gas recirculation. An experimental and modeling investigation of the effect of nitric oxide on the ignition of C1 to C3 hydrocarbon fuels, namely, CH4, C2H4, C2H6 and C3H6, is presented. These molecules are important intermediate species generated during the decomposition of long-chain hydrocarbon fuel components typically present in jet fuels. Moreover, CH4 and C2H6 are major components of natural gas fuels. Although the interaction between NOx and CH4 has been studied extensively, limited experimental work is reported on C2H4, C2H6 and C3H6. NOx, even in very low concentrations, has previously been shown to effectively enhance the ignition of CH4. As a continuation of previous work with C3H8, ignition delay time measurements were obtained using a flow reactor facility with the alkanes (CH4 and C2H6) and olefins (C2H4 and C3H6) at 900 K and 950 K temperatures with 15 mole% and 21 mole% O2. Based on the experimental data, the overall effectiveness of NO in promoting ignition is found to be: CH4 > C3H6 > C3H8 > C2H6 > C2H4.
CSE’s detailed kinetic mechanism, developed for natural gas fuel components, is used for model predictions as well as for sensitivity and species flux analyses. As expected, the reaction between HO2 and NO plays a critical role in promoting the ignition by generating the OH radical while converting NO into NO2. In addition, various important fuel-dependent reaction pathways that promote the ignition of these fuels are identified. H-atom abstraction by NO2 has significant contribution to the ignition of C2H4, and C2H6 whereas the reaction between NO2 and allyl radical (aC3H5) is an important route for the ignition of C3H6.