Kinetic Mechanism and Experimental Study of Initial Temperature and Blended Gas Addition on Combustion Characteristics of Coal Bed Methane-Air

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ABSTRACT Coal bed methane (CBM) is a clean energy resource, CH4 and various blends of C2H6, C2H4, CO, and H2 in different proportions were chosen to formulate a surrogate fuel for coal bed methane. The objective was to study the explosion characteristics of coal bed methane while alleviating the computational complexity associated with intricate reaction mechanisms. The explosion properties (peak explosion pressure (P max) and the maximum pressure rise rate (dp/dt) max) of the mixtures were tested. The unstretched laminar burning velocity (U l ) of the surrogate components was determined under a range of initial temperatures (T u ) (298–373 K) and blended fuel concentrations (0.4–2.0%). Two simplified kinetics models for the surrogate fuel were developed using the GRI Mech 3.0 and USC Mech II mechanisms. These models were constructed through the application of a direct relation graph with error propagation (DRGEP) and full species sensitivity analysis (FSSA). To assess the accuracy of the models, simulations based on these simplified mechanisms were compared with both the detailed mechanism and experimental data. Additionally, sensitivity analyses, utilizing the simplified mechanism, were conducted in order to identify precisely the reactions that govern the interaction dynamics between blended fuel and methane. Within the range of the experimental conditions, the results indicated that P max decreased linearly and with increasing initial temperature. (dp/dt) max was only slightly sensitive to the variation in the initial temperature. However, U l increased with increasing initial temperature, as expected. When blended fuel was added to a 7% CH4-air mixture, P max, (dp/dt)max, and unstretched U l exhibited increasing trends. An equation was derived using the experimental data, to forecast changes in U l across elevated temperatures and blended gas concentrations. The simplified mechanism model successfully replicated the results of the detailed mechanism model and demonstrated good agreement with experimental data concerning species concentrations, ignition delay times, and the U l of the coal bed methane surrogate fuel. Compared to sample 2, the chemistry of sample 1 exhibits greater sensitivity toward intermediate temperature reactions, particularly at higher temperatures.