Influence of injection scheme on flame characteristics in partially premixed combustion Zhao Shilong a , Fan Yuxin a, * , Tiantai Deng b , Danny Crookes b a College of Energy and Power, Nanjing University of Aeronautics and Astronautics, Nanjing, 210016, China b School of Electrical and Electronic Engineering and Computer Science, Queen’s University Belfast, Belfast, BT7 1NN, UK article info Article history: Received 25 January 2019 Received in revised form 13 May 2020 Accepted 3 June 2020 Available online 9 June 2020 Keywords: Injection scheme Integrated stabilizer Partial premixed combustion Enhanced image processing method Fuel distribution Flame expansion abstract A remodelled flame holding device was integrated with injection, which could meet the demand of compact design and better resisting thermal ablation. Simplified model was applied to simulate flow field using CFD and was well verified, and the deviation was within 3%. The optimized stabilizer with close-coupled injection was put forward, its fuel distribution and flame expansion were improved with the growth of velocity. And the greater turbulent intensity was beneficial for droplets breakup and fuel/ air mixing. Additionally, the growth of temperature enlarged flame expansion due to its bigger reaction rates. To more specifically illustrate combustion characteristics, an enhanced image processing method through removing flame radiation was developed to detect real flame boundary. Quantitative analysis of flame expansion was investigated to reveal the working mechanism of integrated scheme. Moreover, the influences of injection locations including prepositive and postpositive injection on flame expansion were investigated and the prepositive injection achieve up to 10% larger flame expansion. Integrated scheme was extremely important for next generation of propulsion and power system. © 2020 Elsevier Ltd. All rights reserved. 1. Introduction A high-performance combustor is needed to meet the re- quirements of flame stabilization and propagation in a wide oper- ation range, flame-holding systems including flame-holding device, and injection scheme are commonly used to ignite and maintain stable and reliable combustion process[1 ,2]. A large number of re- searches on flame-holding devices have been investigated, such as steps[3], cavities[4,5], struts[6], and pylons[7], etc. The working mechanism of flame-holding devices is same to form low-speed recirculation zone, steps and cavities are as pilot burner to ach- ieve successful ignition, and struts and pylons are as radial stabi- lizer to conduce to flame propagation and expansion. In addition, various injection strategies are essential to achieve high-efficiency combustion process. For example, two-phase jets injected from orifice ejector[8] were experimentally investigated, and it pre- sented that this injection scheme enhanced fluid mixing, reaction and mass transfer rates. Injection strategies determine various combustion modes, namely, premixed combustion, non-premixed combustion and partially premixed combustion. In premixed combustion, fuel is well atomized and mixed before ignition, which is beneficial for improving combustion efficiency. For example, injectors are mounted forwardly in sequential combustor, with fuel injection into vitiated hot gas[9]. With the current trends towards higher turbine discharge temperature and requirement for satisfactory operation over extended fuel/air ratios, flame-holding device in- tegrated with injection is expectative to operate under severe conditions of temperature and pressure to meet the requirements of next generation gas turbine engines[10]. The integration of injection scheme and flame-holding device has various combinations and works differently, due to its inherent mechanism. Fuel injection via port holes or ramps locates at combustor walls, often with additional cavities to ensure flame stabilization and favourable ignition conditions[11]. Also, bluff body is a typical configuration with a central fuel jet passing through its centre. Its flow structures, reaction zone, and dynamics of unstable flames are analysed[12, 13]. Moreover, both gaseous and liquid fuel are injected into crossflow, the droplets breakup and combustion characteristics have been studied primarily. High- speed images of the flame were recorded for each operating con- dition and fuel injection configuration in which time-averaged chemiluminescence imaging was performed. This was done in * Corresponding author. E-mail address: fanyuxin@nuaa.edu.cn (F. Yuxin). Contents lists available at ScienceDirect Energy journal homepage: www.elsevier.com/locate/energy https://doi.org/10.1016/j.energy.2020.118058 0360-5442/© 2020 Elsevier Ltd. All rights reserved. Energy 205 (2020) 118058