Numerical Analysis of the Combustion in Micro Gas Turbine with Methane/Biogas Fuels

Replacing natural gas with the environmentally sustainable biogas is a promising way to reduce the usage of fossil fuels and promote organic waste utilization. Micro gas turbine (MGT), as a common power supply machine, is capable of adopting biogas as the fuel. Given the different intrinsic components between natural gas and biogas, combustion performance of biogas in MGT was studied in this work. The effects of fuel composition and excess air coefficient on combustion performance were analyzed through three-dimensional numerical simulation of the MGT combustor. RNG k-e turbulent model, eddy-dissipation/finite rate model, and eight-step reaction mechanism were adopted in the simulation. The results showed that when the CO2 percentage in biogas increases, the NO and CO emissions decreases. However, the fuel rate and pressure drop of combustion chamber increases to maintain constant thermal input. The overall high velocity also increases the requirement for materials of combustion chamber. Furthermore, the average temperature of whole combustor decreases when the excess air coefficient increases. Accordingly, the CO2 mole fraction in biogas should be controlled below 30% and the optimal range of the excess air coefficient is 2–2.5 for the MGT.