Tackling Combustion Instability in Low-Emission Energy Systems: Mathematical Modelling, Numerical Simulations and Control Algorithms

Lead Research Organisation: University College London
Department Name: Mechanical Engineering

Abstract

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Description The project has studied the effects of acoustic waves on panar and curved premixed turbulent flames. Both single-frequency and wideband acoustic excitation have been deployed. Different wave amplitudes have been considered. A direct numerical simulation (DNS) method has been developed, incorporating realistic chemistry and detailed transport model. The DNS and theoretical analysis reveal that strong flame front oscillations when curved flames are excited by acoustic waves of both a single and wideband frequencies. The same setup but with a planar flame shows no such a flame instability. The difference is attributed to the presence of strong Taylor instability or baroclinic torque in the curved flame, which arises from the misalignment between the pressure gradient and the density gradient at the flame fronts. The resulting vortice generation leads to periodic change in the shape of the flame fronts, such an instability is likely to be coupled with the Rayleigh-Taylor instability and Kelvin-Holmholtz instability to augment the effect. Consequently, the reaction rate fluctuation in a curved flame is much stronger than in a planar flame subjected to an acoustic wave, causing the curved premixed flame front to oscillate back and forth in the axial direction. In a curved flame, the acoustic energy is increased by about 40% from the fresh gas to the burnt gas sides, compared to less than 9% for the same conditions for a planar flame. When exciting the curved flame with a single frequency, a dynamic equilibrium or limit cycle oscillation establishes after a few cycles, but the equilibrium time depends on the relevant parameters such as the frequency. The amplitude of the total fuel consumption increases at first linearly with increasing amplitude of the acoustic wave. Fuel consumption rate is increased most for a certain single-frequency excitation, with a lower increase for both higher and lower frequencies. The wideband excitation leads to more pronounced oscillation in the fuel consumption rate compared with any single frequency. A slight enhancement in flame instability has been observed when an oblique acoustic wave interacts with the curved flame compared with a normal acoustic wave, again due to baroclinic torque effects. The curved flame - acoustic interaction has been found to be also affected by the Lewis number effect. The study considers not only non-unity Lewis numbers for various species but also spatial variations of the Lewis numbers. The latter change rapidly across the flame front. The flame front distortion is more severe in the case of constant, unity Lewis number as compared with the case with non-uniform, non-unity Lewis numbers, where the non-coordinated diffusion of species inhibits the flame front movement. Interestingly, the Lewis numbers also have an influence on the amplitude of the limit cycle oscillations. The numerical results have been validated whenever there are experimental data. The theoretical analysis has been conducted in collaboration with project partners at Imperial College London.
Exploitation Route Due to the importance of gas turbines in the energy and defence sectors, the economic, environmental and social impact of the proposed research is enormous. The stake is particularly high for the UK as gas turbines are some of the most important UK exports to the outside world. The plan is to exploit the research results with our project partners Rolls-Royce and Siemens Industrial Gas Turbines. There may be a need for further research on low-cost predictive tools, based on findings from the present research, to facilitate industrial research and design.
Sectors Aerospace, Defence and Marine,Energy,Environment,Manufacturing, including Industrial Biotechology,Transport
 
Description The findings from the project have been disseminated through a large number of invited lectures at international conferences, public lectures and seminars in the UK and abroad. 1. "Multiscale Simulation of Multi-Physics Processes in Combustion," 22nd International Congress on Mechanical Engineering (COBEM2013), Ribeirão Preto, Brazil, November 3-7, 2013. (Keynote Lecture). 2. "Multiscale Simulation of Multi-Physics Processes in Combustion," UNESP, Brazil, 1 November, 2013. (Invited Seminar). 3. "Computational Combustion: Past, Present and Future," Beijing Institute of Technology, Beijing, China, 5 June, 2014. (Invited Seminar). 4. "Towards Understanding Sub-Grid Scale Phenomena in Simulation of Multiphase Combustion," Sandia National Laboratories, USA, 11 August, 2014. (Invited Seminar). 5. "Flow and Combustion Simulation Across the Scales," Institute of Applied Physics and Computational Mathematics, Beijing, China, 21 January, 2016. (Invited Seminar). 6. "Seeing Is Believing: The Interplay of Flow, Flame and Heat Transfer Across Scales," Shanghai Jiao Tong University, Shanghai, China, 7 July, 2016 (Invited Seminar). 7. "Aeroengine-oriented numerical simulation of fluid mechanics, aeroacoustics and combustion," AECC Commercial Aircraft Engine Co. Ltd, Shanghai, China, 29-30 November, 2016. (Invited talk). 8. "Unlocking Mysteries of Flow and Combustion through High-Fidelity Numerical Simulations," South China University of Science and Technology, Shenzhen, China, 7 March, 2017. (Invited Seminar). The audiences were from various industrial sectors, policy makers and the general public who were concerned about the impact of emissions on health, the environment and the climate.
First Year Of Impact 2013
Sector Aerospace, Defence and Marine,Chemicals,Communities and Social Services/Policy,Education,Energy,Environment,Healthcare,Transport
Impact Types Societal,Policy & public services
 
Description EPSRC Standard Grant
Amount £580,960 (GBP)
Funding ID EP/J020184/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 01/2014 
End 09/2015
 
Description Enhancement and Control of Turbulent Reactive Flows via Electrical Fields - A Mesoscopic Perspective
Amount £357,032 (GBP)
Funding ID EP/S012559/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 02/2019 
End 01/2022
 
Description Mechanisms and Synthesis of Materials for Next-Generation Lithium Batteries Using Flame Spray Pyrolysis
Amount £387,989 (GBP)
Funding ID EP/T015233/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 03/2020 
End 03/2023
 
Description The Royal Academy of Engineering Research Exchanges with China and India Scheme
Amount £12,000 (GBP)
Organisation Royal Academy of Engineering 
Sector Charity/Non Profit
Country United Kingdom
Start 04/2012 
End 09/2013