Contents lists available at ScienceDirect Thermal Science and Engineering Progress journal homepage: www.elsevier.com/locate/tsep Investigation of a reverse-cross flow combustor with varying fuel injection momentum Shreshtha Kumar Gupta, Vaibhav Kumar Arghode ⁎ Department of Aerospace Engineering, Indian Institute of Technology, Kanpur 208016, India ARTICLE INFO Keywords: Gas turbine combustors Reverse-cross flow Fuel injection momentum Recirculation ratio Residence time distribution Emissions (CO & NO x ) ABSTRACT The primary objective of this work is to aid the design of a gaseous fuelled reverse-cross flow combustor based on critical factors such as flow field, temperature field, residence time distribution and recirculation ratio of the product gases inside the combustor. In the present work, the effect of fuel injection momentum on these critical factors is investigated by using different fuel injection diameters at same equivalence ratio. The effect of var- iation of equivalence ratio for the highest fuel injection momentum case (smallest fuel injection diameter) is also studied. A lab scale combustor with full optical access having reverse-cross flow geometry is employed for experimental analysis. Three-dimensional computations were performed on a geometrical model of this com- bustor under reacting flow conditions using a commercial software ANSYS-Fluent. Methane is used as the fuel. The numerically calculated flow field inside the combustor is observed to be very sensitive to the fuel injection momentum. As the fuel injection momentum increases, the air jet gets deflected and this significantly affects the flow field inside the combustor such that the recirculation ratio profile changes and the residence time dis- tribution becomes unfavourable. Experimentally obtained OH * chemiluminescence images suggest that the re- action zone moves upward with increase in fuel injection momentum and its intensity increases with increase in equivalence ratio. The measured CO and NO x emissions at exhaust suggest that CO increases and NO x decreases with increase in fuel injection momentum. It is found that the effect of fuel injection momentum is pronounced when the fuel injection momentum is higher than a critical value, above which, the flow field, thermal field, and the reaction zone location are affected significantly. 1. Introduction The scientific research and industrial applications have indicated that the distributed combustion, also called as colorless [1], flameless [2–5] or MILD [6–10] combustion, is one of the most promising com- bustion technologies to facilitate low pollutant emissions and stable combustion. To achieve distributed combustion, product gases are re- circulated such that the oxidizer (mixture of air and product gases) temperature is above the fuel autoignition threshold [11]. Under these conditions, combustion is spontaneous and flame appears to have lower visible and audible intensity. In order to investigate the performance of combustors operating in distributed combustion regime, several geo- metries with varying thermal intensities and different combinations of air and fuel injection locations have been investigated [12–16]. It is found that the reverse-cross flow geometry shows favourable combus- tion characteristics [17]. In reverse-cross flow combustor, air is injected from the exit end, resulting in overall reverse flow pattern of gases inside the combustor, and the fuel is injected perpendicular to the air jet, resulting in cross- flow injection of fuel with respect to the air jet. Recirculation of hot product gases and the residence time distribution of gases inside the combustor are important design parameters for such combustors [18]. Combustion is stabilized due to recirculation of a substantial portion of hot product gases which mixes with fresh inlet reactants to form hot and diluted reactant mixture prior to combustion [19]. Due to this, combustion occurs in distributed and kinetically controlled regime. The amount of recirculation of product gases can be quantified by a para- meter called recirculation ratio, which is defined as the ratio of the entrained mass flow rate of product gases to the fresh incoming air plus fuel mass flow rate. The residence time of gases inside the combustor play an important role for the CO emissions. High thermal intensity (heat release rate per unit volume of the combustor) results in lower residence time of gases inside the combustor which results in high CO emissions [20]. Un- favourable residence time distribution, in which there is a large fraction of gases having low residence time, can also lead to higher CO https://doi.org/10.1016/j.tsep.2019.02.006 Received 23 October 2018; Received in revised form 12 January 2019; Accepted 20 February 2019 ⁎ Corresponding author. E-mail address: varghode@iitk.ac.in (V.K. Arghode). Thermal Science and Engineering Progress 10 (2019) 232–244 2451-9049/ © 2019 Elsevier Ltd. All rights reserved. T