Investigation of Air/Fuel Mixing Flow in Non-Premixed Burners

Abstract

Nowadays, combustion process is being used in different industries and human applications. Combustion quality and exiting pollutants level have been so important these days because of ever-increasing of environmental pollutants. One of the factors that affect the combustion quality of non-premixed burner is the way that fuel and air is being mixed. In order to achieve a flame with higher efficiency, the ratio between fuel and air must be kept in appropriate limit. Theoretically, the best mixture is the one that consist of efficient air that could burn fuel perfectly. This type of mixture is called stoichiometric mixture. Therefore, in order to increase combustion efficiency and take more energy from fuel, the fuel/air mixture must be close to stoichiometric conditions. In this research, first we simulated the fuel/air flow patterns and observed the way that they are being mixed together in a Strong Jet/Weak Jet burner. Different states of mixing and distribution of fuel/air in chamber has been reached by some changes in geometry and flow pattern of the initial case. Parameters such as fuel nozzle diameter, fuel injection angle and the number of fuel/air nozzles are being assumed to have effects on the ways of flows mixing. It could be said that whenever the mixture fraction was close to stoichiometric conditions, combustion with higher quality is achieved. On the Other hand, uniformity of mixture fraction in mixing field is more desirable. Finally, after the validation of combustion models, combustion flows is being simulated in two sample burner with different level of mixing. The results showed that the more uniform mixing was, the more uniform temperature has been reached. But, the level of CO emission has been increased. This was because of more local fuel in improved geometry. Increasing level of CO does not necessarily result in low quality combustion. Because of higher air/fuel ratio in the initial case, the combustion with low temperature has been formed and some parts of fuel go out from the outlet without any chemical reaction.