Stabilization and Dynamic of Premixed Swirling Flames: Prevaporized, Stratified, Partially, and Fully Premixed Regimes focuses on swirling flames in various premixed modes (stratified, partially, fully, prevaporized) for the combustor, and development and design of current and future swirl-stabilized combustion systems. This includes predicting capabilities, modeling of turbulent combustion, liquid fuel modeling, and a complete overview of stabilization of these flames in aeroengines. The book also discusses the effects of the operating envelope on upstream fresh gases and the subsequent impact of flame speed, combustion, and mixing, the theoretical framework for flame stabilization, and fully lean premixed injector design. Specific attention is paid to ground gas turbine applications, and a comprehensive review of stabilization mechanisms for premixed, partially-premixed, and stratified premixed flames. The last chapter covers the design of a fully premixed injector for future jet engine applications. - Features a complete view of the challenges at the intersection of swirling flame combustors, their requirements, and the physics of fluids at work - Addresses the challenges of turbulent combustion modeling with numerical simulations - Includes the presentation of the very latest numerical results and analyses of flashback, lean blowout, and combustion instabilities - Covers the design of a fully premixed injector for future jet engine applications

Developing clean, sustainable energy systems is a pre-eminent issue of our time. Most projections indicate that combustion-based energy conversion systems will continue to be the predominant approach for the majority of our energy usage. Unsteady combustor issues present the key challenge associated with the development of clean, high-efficiency combustion systems such as those used for power generation, heating or propulsion applications. This comprehensive study is unique, treating the subject in a systematic manner. Although this book focuses on unsteady combusting flows, it places particular emphasis on the system dynamics that occur at the intersection of the combustion, fluid mechanics and acoustic disciplines. Individuals with a background in fluid mechanics and combustion will find this book to be an incomparable study that synthesises these fields into a coherent understanding of the intrinsically unsteady processes in combustors.

This book provides a rigorous treatment of the coupling of chemical reactions and fluid flow. Combustion-specific topics of chemistry and fluid mechanics are considered and tools described for the simulation of combustion processes. This edition is completely restructured. Mathematical Formulae and derivations as well as the space-consuming reaction mechanisms have been replaced from the text to appendix. A new chapter discusses the impact of combustion processes on the atmosphere, the chapter on auto-ignition is extended to combustion in Otto- and Diesel-engines, and the chapters on heterogeneous combustion and on soot formation are heavily revised.

Implementing the combustion strategy of lean premixed (LPM), gas turbines can significantly reduce regulated emissions from the combustion process but are susceptible to thermoacoustic instabilities. With the use of time-resolved PLIF and dynamic pressure transducers, the coupling between the flame structure and pressure was used to characterize the instability. Without the porous insert, the pressure measurements revealed a strong dominate frequency at 340 Hz, which was identical to the oscillation frequency of the OH intensity at different locations are indicating a global instability. The pressure and OH* signal oscillation are coupled with a consistent phase shift. With the addition of the porous insert, the pressure oscillation amplitude was reduced by an order of magnitude with minor peaks observed in the OH spectra indicating a reduction in the thermoacoustic instability while removing the phase relationship previously seen. To verify the importance of the porous structure, a comparison between a solid and porous insert, having identical geometries, was tested. Two regions were produced, one where the inserts have near identical performance, driven by insert geometry, and a second where the porous insert mitigates an instability seen with the solid insert demonstrating the requirement of the porous structure. To verify the ability of a single porous design to be effective over a wide operating range, different thermoacoustic instability modes are produced by adjusting equivalence ratio. For multiple conditions where the porous exhibited external flamelet stabilization the insert is effective at mitigating the thermoacoustic instability, but when the flamelets subside into the insert a thermoacoustic instability was seen. With the requirement of external stabilization meet, distinct instability modes were eliminated thus giving evidence a single porous insert design mitigates thermoacoustic instabilities across a range of inlet conditions. Finally a potential relationship between expansion ratio and total SPL is investigated for a lean direct injection (LDI) system. With a combustor diameter of 50 mm, the LDI system demonstrates cyclic flame structures indicating its susceptibility of thermoacoustic instability. Further the dominating frequencies observed in dynamic pressure and OH* signal are identical signifying a coupling between the flame intensity and pressure oscillations.

A work on turbulent premixed combustion is important because of increased concern about the environmental impact of combustion and the search for new combustion concepts and technologies. An improved understanding of lean fuel turbulent premixed flames must play a central role in the fundamental science of these new concepts. Lean premixed flames have the potential to offer ultra-low emission levels, but they are notoriously susceptible to combustion oscillations. Thus, sophisticated control measures are inevitably required. The editors' intent is to set out the modeling aspects in the field of turbulent premixed combustion. Good progress has been made on this topic, and this cohesive volume contains contributions from international experts on various subtopics of the lean premixed flame problem.

In a similar fashion, increasing the pressure was found to alter the flame shape and flame extent, but the thermo-acoustic coupling and induced large scale structure persisted to 0.34MPa, the highest pressure tested.

Reviews our current understanding of the subject. For graduate students and researchers in computational fluid dynamics and turbulence.

November, 2008 Anna Schwarz, Johannes Janicka In the last thirty years noise emission has developed into a topic of increasing importance to society and economy. In ?elds such as air, road and rail traf?c, the control of noise emissions and development of associated noise-reduction techno- gies is a central requirement for social acceptance and economical competitiveness. The noise emission of combustion systems is a major part of the task of noise - duction. The following aspects motivate research: • Modern combustion chambers in technical combustion systems with low pol- tion exhausts are 5 - 8 dB louder compared to their predecessors. In the ope- tional state the noise pressure levels achieved can even be 10-15 dB louder. • High capacity torches in the chemical industry are usually placed at ground level because of the reasons of noise emissions instead of being placed at a height suitable for safety and security. • For airplanes the combustion emissions become a more and more important topic. The combustion instability and noise issues are one major obstacle for the introduction of green technologies as lean fuel combustion and premixed burners in aero-engines. The direct and indirect contribution of combustion noise to the overall core noise is still under discussion. However, it is clear that the core noise besides the fan tone will become an important noise source in future aero-engine designs. To further reduce the jet noise, geared ultra high bypass ratio fans are driven by only a few highly loaded turbine stages.