Numerical Simulations of Nitric Oxide (NO) Formation in Methane, Methanol and Methyl Formate in different Flow Configurations

Abstract

Methane/air, methanol /air and methyl formate /air have been numerically simulated in three different flow configurations: homogeneous system; freely propagating flame; and diffusion flame. These simulations have been done with an aim of establishing the influence of fuel oxygenation on generation of pollutant. Various chemical kinetic mechanisms have been employed and extensively tested so as to ensure validity of the results. For each of the three configurations, a comparison of temperature, NO and its immediate dominant precursor species (CH and N) concentration profiles in the three fuels have been done. It has been established that, under the different flow configurations considered, CH4 has high amount of total NO present in the flame region as compared to the oxygenated fuels (CH3OH and CH3OCHO). The temperatures attained in freely propagating and diffusion flames are relatively low (approximately ≤ 2000 K). This temperature favours prompt-NO formation, and therefore, a significant difference of the amount of NO (one order of magnitude higher) is observed in CH4 as compared to oxygenated fuels due to low values of CH and N observed in these fuels (CH3OH and CH3OCHO). High flame temperatures (approximately 2900 K) due to high initial temperatures are observed in the homogeneous system. Therefore, in homogeneous system it was observed that the amount of NO produced by the three fuels is within the same order of magnitude due to availability of the O atoms and nitrogen molecules (important species in thermal NO mechanism (Zel'dovich mechanism)).