Effect of Adding Water Content in the Fuel on Soot Formation and Pollutant Emission in Methane Combustion by CFD Simulation

Owing to the major source of energy production, combustion technologies are commercially available throughout the world. However, combustions are responsible for too much atmospheric pollution which is detrimental to human health and environment. Thus concerted efforts are being made to reduce the particle emissions due to soot formation caused by incomplete combustion and acid precipitation originating mainly from Nitrogen Oxide (NOx) during combustion process at high temperature. However, with the emergence of new fuels and combustion modes, it is necessary to improve the computational models. Hence turbulent combustion needs to be optimized through better understanding to meet demands for lower emissions without sacrificing power and fuel consumption. In fact, emission reduction measures can possibly be developed by understanding the mechanism of pollutants formation during combustion process, which requires knowledge of trace species. These species are produced by finite rate chemical kinetic mechanisms that involve large numbers of elementary steps. For this purpose, the application of a 3D Computational Fluid Dynamics (CFD) model simulations are proven to be very effective to support the experimental investigations of turbulent combustion. In the present paper, CFD simulation of combustion has been reported in order to reduce the pollutant emission and soot formation. The Pollutant reduction is performed on well-validated comprehensive mechanism that was designed to simulate the combustion of natural gas (methane-air) constituents and production of NOx and sooth, and model is able to predict the NOx emission levels with all possible gas phase reaction mechanism such as thermal, prompt, and nitrous oxide taken into account. The reaction rates of pollutant formation in combustors are determined by both chemical kinetics and turbulence and modeled using eddy-dissipation mode. The combustion is simulated by steady-state governing equations solved using the SIMPLE algorithm and the effect of turbulence on the mean flow field was accounted for using the RNG k- turbulence model, this non-premixed type combustion is molded using ANSYS Fluent-species transport model, followed by single-step reaction mechanism and NOx model assuming conversion of the fuel to CO2, H2O, NO and NO2 etc. The reaction mechanism is validated for using constant-volume combustion chamber experiments. Further, the model is also validated for inlet diffusion and diffusion energy source. The flow parameters like velocity, temperature, and mass fraction are defined prior to the simulation. In the work presented in this thesis, the first part focused on the effect of numerical variation in mass fraction of different species during the process using line probes at different location of combustor has been studied and plotted CO2, H2O, CH4, N2, O2 and NOx emission and Soot formation accordingly. In the second part of the research, an attempt has been made by adding water content in the fuel by 5% to 30% by mole in order to predict its effects on the result for sooth and emission reduction using methane-air two steps as a mixture material followed by parametric study approach. Consequently, the optimal values were evaluated and model is able to predict the reduction in NOx emissions and sooth formations when natural gas (methane-air) is used.