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International Heat Transfer Conference 11

ISSN: 2377-424X (online)
ISSN: 2377-4371 (flashdrive)

EFFECT OF TURBULENT TRANSPORT AND MIXING ON FLAME ACCELERATION THROUGH HIGHLY BLOCKING OBSTACLES

M. Jordan
Lehrstuhl A fur Thermodynamic Technische Universitat Munchen, Germany

Nikolai Ardey
Lehrstuhl A fur Thermodynamik Technische Universitat Mttnchen 85747 Garching Germany

Franz Mayinger
Lehrstuhl A für Thermodynamik, Technische Universität München, München, Germany; Technical University, Hannover, FRG Institut fur Verfahrenstechnik

Marco N. Carcassi
Dipartimento di costruzioni meccaniche e nucleari Universita di Pisa via Diotisalvi 2 Pisa 56126 Italy

DOI: 10.1615/IHTC11.4270
pages 295-300

Abstrakt

The propagation of gaseous explosions under premixed conditions is governed by both molecular heat and mass transport, and the interaction of the flame front with the turbulent expansion flow generated by the combustion process itself. The molecular transport controls the flame stability and its sensitivity to flame stretching and quenching. Therefore it determines the response of a flame front to flow vorticity, resulting in either flame acceleration or turbulent quenching. The present paper reports on experimental investigations of transport phenomena during flame propagation with highly blocking flow obstacles by means of non-intrusive, optical techniques. It is shown, that turbulent flame quenching processes lead to an acceleration of free radicals behind the obstacle. The mixture of these radicals with the unburned gas leads to an enhanced chemical reaction and an increase ofthe turbulent burning velocity.
A comparison of two different fuels (hydrogen and methane) is presented, strongly differing in molecular behavior due to their different Lewis numbers. The experiments have been performed in two explosion tubes of different scale (PuFlaG facility: ø 80 mm and L.VIEW facility: 0.7×0.7 m) in order to address scaling effects. Blocking ratios between 95% and 99.7% have been investigated.
A high-speed video-camera operated a; repetition rates of up to 9000 images/sec is used to record the self-fluorescence of the flame and to visualize the flame propagation. The path of the hot gas is recorded via Schlieren photography with the high-speed video-camera. The OH-radicals in the cross section of the flame are visualized with laser induced predissociation fluorescence with an exposure time of several nano-seconds.

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