On flameless combustion modeling of fuel oil in ansys fluent
Fuel costs and emission standards for industrial burner applications are becoming increasingly important. The emissions of NOx and CO2 are more stringently regulated and clean fuels are costly. A relative new combustion technique to increase the efficiency and lower the toxic emissions simultaneously is flameless combustion. It has some distinct advantageous characteristics compared to conventional combustion and is increasingly researched in the last two decades. The emphasis in early research was primarily on gaseous fuels, but considering price and availability, lower grade fuels like Heavy Fuel Oil (HFO) are gaining attention.
Computational Fluid Dynamics (CFD) modeling is a cost effective way to research and develop combustion appliances. The objective of this thesis is to investigate and develop a method to model flameless combustion in combination with heavier liquid fuels in the commercial available software package ANSYS Fluent. This is done by validating a set of numerical models against semi-industrial flameless combustion experiments with fuel oil.
The numerical model is built around the Eddy Dissipation Concept (EDC) model in combination with a Light Fuel Oil (LFO) surrogate fuel n-heptane. This fuel is implemented by a chemical reaction mechanism. The validation case is succeeded by investigating the model behavior due to oxygen dilution. The model shows the expected phenomena due to dilution, but at the same time, the solution becomes unreliable with a view to element conservation. In order to research the model behavior in conditions which correspond more to boilers instead of furnaces, the inlet gas and wall temperatures are lowered to more practical levels. The model shows reduced combustion intensity at lower temperatures, but it also results in unexpected end results. This requires more attention and investigation if this model should be applied in similar cold or diluted conditions.