Experimental and Modeling Study of C1-C3 Hydrocarbon Ignition in the Presence of Nitric Oxide

Abstract

Nitric oxide (NO) produced during combustion will be present in vitiated air used in many devices. An experimental and modeling investigation of the effect of NO on the ignition of C1-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. As a continuation of previous work with C3H8, ignition delay time (IDT) 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. A detailed kinetic mechanism is used for model predictions as well as for reaction path analysis. The reaction between HO2 and NO plays a critical role in promoting the ignition by generating the OH radical. In addition, various important fuel-dependent reaction pathways also promote the ignition. 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.