C. Heeger

Experimental and Theoretical Investigation of the Flashback of a Swirling, Bluff-Body Stabilised, Premixed Flame

Abstract Flashback of an open turbulent, premixed flame in a swirl burner with central bluff-body is considered. The aim is to obtain further understanding of the physical mechanisms responsible for the upstream flame propagation. Previous studies on the same configuration hypothesised that there is an adverse pressure gradient in the direction of flame propagation. In this paper this is further investigated experimentally and theoretically. Static gauge pressure is measured on the surface of the bluff-body during flame flashback. Simultaneously, flame luminosity is imaged at 5 kHz. The results indicate that the static pressure rises downstream of the propagating reactive front. This is, then, discussed in the context of the theory of vortex bursting. An existing theory of flame propagation in the core flow is extended to a configuration similar to that investigated experimentally. The theory, although highly simplified, explains the generation of adverse pressure gradient across the flame and is qualitatively consistent with the experiment.

Advanced Laser Diagnostics for Understanding Turbulent Combustion and Model Validation

This contribution is not an original publication but a report of cumulative work that was carried out within the framework of SFB 568. The work was published in different archival journals and figures and text passages have been taken from different journal articles as indicated by the references. The aim of this report is to present experiments in projects B1 and B3 for improving our understanding in turbulent combustion with a focus of turbulent flow and scalar fields as well as their mutual interactions. The report is restricted to generic gaseous turbulent flames that feature different characteristics important to practical applications. The methods presented here are feasible to study boundary conditions, flow and scalar fields and are based all on interactions between laser light and matter. Following a brief introduction, two target flames are discussed in Sect. 4.2. Sections 4.3 and 4.4 exemplify flow and scalar measurements. Section 4.5 discusses combined scalar/flow measurements that can significantly improve our understanding of turbulence-chemistry interactions. In Sect. 4.6 new developments based on high-repetition-rate imaging are highlighted. These diagnostics complement methods at low repetition rate commonly used to generate an understanding by statistical moments and probability density functions. High repetition rate imaging techniques presently are an emerging field. Although the most recent developments achieved in the funding period of the Collaborative Research Center are included to this report, near-future progress in this field will lead to even more interesting insights into combustion phenomena.

Self-exited oscillation in a combustion chamber driven by phase change in the liquid fuel feed system

A new mechanism for the generation of a self-exited oscillation of combustion in a generic combustion chamber typical for aeroengine combustors is described. The cause of the oscillation is the phase change from liquid to vapour which happens when the preheat temperature of the air flowing through the burner exceeds the boiling temperature at the operating pressure and the fuel flow is so low that heat transfer to the liquid fuel causes evaporation within the fuel channels of the burner. Liquid fuel and vapour alternatively enter the airstream of the burner. This leads to an unstable situation for the flame. Measurements of chemiluminescence and liquid fuel show nearly complete extinction and re-ignition for the limit cycle. Prevention of the oscillation is possible by better thermal management of the fuel path.