Research Article The Effects of Air Preheating and Fuel/Air Inlet Diameter on the Characteristics of Vortex Flame Mostafa Khaleghi, 1 S. E. Hosseini, 1 M. A. Wahid, 1 and H. A. Mohammed 2 1 High-Speed Reacting Flow Laboratory, Faculty of Mechanical Engineering, Universiti Teknologi Malaysia (UTM), 81310 Skudai, Johor, Malaysia 2 Department of Environmental Engineering, College of Engineering, Komar University of Science and Technology (KUST), King Mahmud Circle, Sulaymaniyah, Kurdistan, Iraq Correspondence should be addressed to Mostafa Khaleghi; mostafa26 k@yahoo.com Received 28 September 2014; Revised 8 April 2015; Accepted 26 April 2015 Academic Editor: David Kubiˇ cka Copyright © 2015 Mostafa Khaleghi et al. his is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. he efects of fuel/air inlet diameter as well as air preheating on the lame stability, temperature distribution, pollutant formation, and combustion characteristics of a lab-scaled asymmetric vortex lame have been investigated. A three-dimensional steady-state inite volume solver has been used to solve the governing and energy equations. he solver uses a irst-order upwind scheme to discretize the governing equations in the space. he semi-implicit method for pressure linked equations has been applied to couple the pressure to the velocity terms. Several turbulence models were applied to predict the lame temperature and it was found that K- RNG has given the best results in accordance with the experimental results. he results reveal that the inlet air diameter can enhance the thermal properties and reduce the NO  emission while the inlet fuel diameter has less signiicant impact. Increasing diameters are accompanied with a pressure drop. It was found that preheating the air and fuel would signiicantly afect the lame temperature and NO  emission with constant mass low rate. 1. Introduction Emissions of nitrogen oxides (NO  ) are allied with a range of environmental anxieties that include increasing ground level ozone, acidiication of aquatic systems, forest damage, and formation of ine particles in the atmosphere [1–3]. hese anxieties have resulted in a need to reduce emissions in various combustion systems. Vortex combustion has been known for its ability to improve lame stability and decrease NO  formation [4, 5]. Vortex combustion is widely employed in furnaces and gas turbine combustors. Due to the wide industrial applications of vortex combustion, there has been a considerable amount of research on such lames, both pre- mixed and nonpremixed. he irst discussion of vortex lames was reported in 1998 by Gabler [6]. he turbulent vortex lame was described for the irst time in such work by both exper- imental and computational methods. he major objective of Gabler’s work was to identify the possible reduction in pollu- tant formation from vortex lames. A concise description of the lame anatomy was presented, and some of the basic fea- tures of vortex lames were reported. hese features include the enhanced stability near the lean lammability limit of the fuel and some primary temperature proiling. In previous studies, a description of the lame anatomy was presented, and some of the basic features of vortex lames were reported. hese features include the enhanced stability near the lean lammability limit of the fuel and some primary temperature proiling [7, 8]. Recent issues in the vortex combustion could be found in modern gas turbines, which rely on premixed combustion to reduce NO  emissions but are more sensitive to resonant coupling, leading to instability [9–11]. Gas turbine combustion dynamics have been considered in a series of articles edited by Lieuwen and Yang [12]. Efect of the oxygen concentration, preheating, pressure, and equivalence ratio Hindawi Publishing Corporation Journal of Energy Volume 2015, Article ID 397219, 10 pages http://dx.doi.org/10.1155/2015/397219