Development of Well-Validated Global Kinetic Mechanisms for Predicting CO in Partially Premixed and Non-premixed Methane–Air Flames

The world-wide use of natural gas and biogas has increased tremendously for harvesting energy for power production, transportation, domestic, and industrial sectors. The main component in biogas and natural gas is methane (CH4), whose combustion in gas burners is vital in research purposes and in many practical applications. A well-validated global kinetic mechanism is necessary to numerically simulate its combustion with less computational cost. However, these global mechanisms generally do not predict carbon monoxide (CO) well. In this study, two widely used mechanisms, namely 2-step mechanism of Westbrook and Dryer and 4-step mechanism of Jones and Lindstedt are considered for predicting the atmospheric partially premixed and non-premixed methane–air flames. The discrepancies in the predictions of CO, CO2, and CH4 by these two global mechanisms are identified and improved for all flame configurations by opting for systematic rate revision of important reactions. The rates of methane consumption (R1) and CO2 dissociation (R2) reactions in the 2-step mechanism are increased by a factor of 2 and 1.5, respectively, in order to get better predictions of CH4, CO, and CO2 amounts. Similarly, the rates of two methane consumption reactions (R1 and R2) to produce CO in the 4-step mechanism are decreased and increased by a factor of 50 and 1.5, respectively. The proper choice of reactions and its associated rate modifications in the both 2-step and 4-step mechanisms resulted in the improved predictions of temperature and major species amounts in partially premixed and non-premixed flame configurations. A multidimensional reactive flow simulation can be done at low computational cost using the developed 2-step modified mechanism if the fuel component has only methane and CO in it, whereas the 4-step mechanism is used when the fuel components (such as syngas) also contain hydrogen along with methane and CO.