Numerical analyses of diluent effect on combustion characteristics under colorless distributed combustion conditions

In this study, colorless distributed combustion conditions (CDC) which is a novel combustion method have been examined as numerical by using methane and hydrogen enriched methane mixtures fuels. In order to achive CDC conditions, oxidizer has been diluted with N2 / CO2 under different oxygen concentrations, 21% to 13%. Moreover, to be able to observe oxidizer pre-heating effect, numerical analyses have been conducted with 300K and 600K oxidizer temperatures. Selected combustion chamber created swirl flows through symmetrically located two fuel inlet and two oxidizer inlet sections. Fuel flow rates have been arranged based on thermal power of 2 kW. Oxidizer flow rates have been calculated by taking into account various equivalence ratio and dilution ratios. In addition that, fuel and oxidizer inlet structures on combustion have been investigated by comparing as both parallel and cross flows. All these analyses have been implemented by using Ansys Fluent computational fluid dynamics commercial codes. In order to make more accurate turbulence flow predictions, Reynold Stress Model has been used. In summary, CDC conditions have been provided with broadened flame structure throughout cumbustion chamber, flame stability, uniformly temperature distribution, ultra low NOX and low CO emissions levels. Especially, predicted flame instabilities along with hydrogen addition have been eliminated with CDC.