Combustion dynamics of turbulent swirl flames with hydrogen addition

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

Abstract

Combustion instabilities represent one of the most serious problems hindering the development of low-emission aero- and industrial- gas turbine combustors. In order to achieve efficient, low-emissions performance fuel-lean and preferably premixed operating conditions are necessary. However, these lean combustors have the drawback of being particularly susceptible to thermo-acoustic instability. These instabilities are characterised by strong pressure oscillations in the combustion chamber due to a complex interaction between thermo-acoustic and fluid-dynamic processes. When the pressure or velocity oscillations couple favourably with the unsteady heat release, large-amplitude self-sustained oscillation may result. These high amplitude oscillations can have a detrimental effect on combustor performance and may cause catastrophic failure of the system. Lean premix concept is increasingly adopted by gas turbine engine manufacturers to reduce emissions and increase fuel economy. Although fuel lean conditions reduce NOx emissions by decreasing the flame temperature, lean flames are particularly susceptible to combustion oscillations and blow-off. Hydrogen enrichment is one of the promising methods that can be used to improve the stable operation of the combustor under extremely lean conditions. Hydrogen enrichment also improves the ignitability and the response of the flame to strain and curvature. These benefits suggest a promising role for hydrogen enrichment in the development of low-emission gas turbine combustion technology. However, the response of the hydrogen enriched flames in the context of combustion instability is not fully understood. Thus, the primary motivation of this study is to understand and underpin the mechanisms of heat release modulation with hydrogen addition in the context of combustion oscillations. There are several well known mechanisms that can promote fluctuations in the heat release in lean flames; namely, variations in mixture ratio, sensitivity of the flames to pressure/velocity oscillations, and the formation and shedding of vortices. Any of these mechanisms can cause combustion oscillations to grow in amplitude through positive feedback until a self-sustaining limit-cycle amplitude is reached. However, there is often a clear distinction between the mechanisms driving linear growth of instability and those which cause the heat release oscillations to saturate to limit-cycle conditions. In order to predict and control combustion instabilities effectively the transition from linear growth to non-linear saturation and the mechanisms governing this transition has to be better understood, especially in industrial type non-/partially premixed flames with hydrogen addition. This proposal aims: a) to study and compare mechanisms of heat release oscillations in bluff-body and swirl stabilised turbulent flames, b) to investigate the effect of flame anchoring and that of spatial and temporal mixture variation, which are relevant to limit-cycle oscillation in practical combustors, and c) to assess and understand the role of hydrogen addition in improving the dynamic stability of the combustor, using simultaneous measurements of flow and heat release via advanced laser diagnostic techniques. The expected outcome of this project is to underpin the mechanisms of combustion oscillations in turbulent flames relevant to practical combustors. In particular, the proposed experiments will highlight the role of flame stabilisation, equivalence ratio variation and hydrogen addition on the non-linear flame response, which is of significant importance for improving the fundamental understanding and prediction of the limit-cycle oscillations in practical combustion systems. This research will lead to development of non-linear flame models for acoustic analysis and also aid the development of new control strategies for elimination of combustion oscillations in industrial combustors.

Publications

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Dowlut A (2012) 19th International Congress on Sound & Vibration in Experimental investigation of dynamic response of acoustically forced turbulent premixed CH4/CO2/air flames.

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Hussain T (2010) Fifth European Combustion Meeting. Cardiff, Great Britain in Experimental Investigation of Response of Hydrogen Enriched Methane Flames to Acoustic Oscillations

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Hussain T (2012) 19th International Congress on Sound & Vibration. Vilnius, Lithuania in Investigation in to the effect of hydrogen enrichment on the response of turbulent premixed flames subjected to acoustic excitation

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Hussain T (2011) 18th International Congress on Sound & Vibration. Rio de Janeiro, Brazil in Investigation of the effect of fuel stratification on response of turbulent premixed flames to acoustic excitation

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Kariuki J (2016) Heat Release Imaging in Turbulent Premixed Ethylene-Air Flames Near Blow-off in Flow, Turbulence and Combustion

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Kariuki J (2015) Heat release imaging in turbulent premixed methane-air flames close to blow-off in Proceedings of the Combustion Institute

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Yuan R (2015) Reaction zone visualisation in swirling spray n -heptane flames in Proceedings of the Combustion Institute

 
Description Detailed experimental investatigation was carried out to understand, from a fundamental viewpoint, the nonlinear combustion dynamics of turbulent bluff-body/swirl stabilised flames, with equivalence ratio non-uniformities and the effect of hydrogen enrichment. The results showed that hydrogen addition is an effective way of reducing flame response and the amplitude of self-excitation in ethylene flames. On the other hand, the effectiveness of flame reponse reduction in methane flames was dependent on flow and acoustic forcing conditions.
Exploitation Route It is envisaged that the high resolution time-space resolved flame and flow data recorded under acousting forcing conditions of turbulent ethylene and methane flames, could be used for validating various industrially relevant computational models. The high resolution time and space resolved flame response data, together with detailed boundary conditions obtained during this project could be used as a validation case of computational and theoretical flame models.
Sectors Energy

 
Description The research enabled detailed understanding nonlinear acoustic flame response of hydrocarbon flames with hydrogen addition. As a part of this project, a new experimental approach in determining local heat release rate was developed. It is envisaged at this technique is applicable for many practical fuel flexible combustion systems.
First Year Of Impact 2011
Sector Aerospace, Defence and Marine,Energy
 
Description EPSRC responsive mode
Amount £416,330 (GBP)
Funding ID EP/P003036/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Academic/University
Country United Kingdom of Great Britain & Northern Ireland (UK)
Start 01/2017 
End 12/2019
 
Title Heat release rate imaging using H atom 
Description A new measurement method was developed. This method will allow imaging/measuring local heat release - a key parameter for combustion analysis - applicable to future low emission systems. 
Type Of Material Improvements to research infrastructure 
Year Produced 2014 
Provided To Others? Yes  
Impact It is envisaged that this method will be adopted by combustion community for fundamental and applied research. 
 
Description Combustor thermoacoustics for multi-burner low emissions gas turbines (CHAMBER) 
Organisation Imperial College London
Country United Kingdom of Great Britain & Northern Ireland (UK) 
Sector Academic/University 
PI Contribution At UCL, I will undertaking experimental research that will provide further input into theoretical/modelling efforts of Dr Aimee Morgans at Imperial.
Collaborator Contribution Dr Aimee Morgans' open source acoustic analysis tool will be employed to model the experimental work at UCL. The joint effort is likely to underpin nonlinear flame, acoustic interaction in multi-burner combustion systems relevant to gas turbine engines.
Impact The work is expected to generate flame transfer (describing) functions relevant to practical combustion devices.
Start Year 2017
 
Description Multi-university partnership on heat release imaging 
Organisation Indian Institute of Technology Madras
Country India, Republic of 
Sector Academic/University 
PI Contribution The measurement method developed in this project, local heat release imaging, was applied to new problems in collaboration with University of Cambridge and Indian Institute of Technology Madras, India (IITM).
Collaborator Contribution University of Cambridge team shared simulation data and their expertise on lean extinction was provided (also helped conduct experiments) IITM research spent time at UCL conducting experiments and undergoing training.
Impact Three publications - DOIs: 10.1007/s10494-016-9720-y 10.1016/j.combustflame.2015.12.023 10.1016/j.combustflame.2015.11.029
Start Year 2014
 
Description Multi-university partnership on heat release imaging 
Organisation University of Cambridge
Country United Kingdom of Great Britain & Northern Ireland (UK) 
Sector Academic/University 
PI Contribution The measurement method developed in this project, local heat release imaging, was applied to new problems in collaboration with University of Cambridge and Indian Institute of Technology Madras, India (IITM).
Collaborator Contribution University of Cambridge team shared simulation data and their expertise on lean extinction was provided (also helped conduct experiments) IITM research spent time at UCL conducting experiments and undergoing training.
Impact Three publications - DOIs: 10.1007/s10494-016-9720-y 10.1016/j.combustflame.2015.12.023 10.1016/j.combustflame.2015.11.029
Start Year 2014