Detailed investigation of ignition by hot gas jets R. Sadanandan a, * , D. Markus a , R. Schießl b , U. Maas b , J. Olofsson c , H. Seyfried c , M. Richter c , M. Alde ´n c a Physikalisch Technische Bundesanstalt, Braunschweig, Germany b Universita ¨ t Karlsruhe, Institut fu ¨ r Technische Thermodynamik, Germany c Lund Institute of Technology, Division of Combustion Physics, Sweden Abstract Experimental and numerical investigations of the ignition of hydrogen/air mixtures by jets of hot exhaust gases are reported. An experimental realisation of such an ignition process, where a jet of hot exhaust gas impinges through a narrow nozzle into a quiescent hydrogen/air mixture, possibly initiating ignition and combustion, is studied. High-speed laser-induced fluorescence (LIF) image sequences of the hydroxyl radical (OH) and laser Schlieren methods are used to gain information about the spatial and tem- poral evolution of the ignition process. Recording temporally resolved pressure traces yields information about ambient conditions for the process. Numerical experiments are performed that allow linking these observables to certain characteristic states of the gas mixture. The outcome of numerical modelling and experiments indicates the important influence of the hot jet temperature and speed of mixing between the hot and cold gases on the ignition process. The results show the quenching of the flame inside the nozzle and the subsequent ignition of the mixture by the hot exhaust jet. These detailed examinations of the igni- tion process improve the knowledge concerning flame transmission out of electrical equipment of the type of protection flameproof enclosure. Ó 2006 The Combustion Institute. Published by Elsevier Inc. All rights reserved. Keywords: Jet ignition; OH LIF; High-speed laser diagnostics 1. Introduction and theoretical background Ignition of fuel/air mixtures by impinging hot gas jets is a very important process in various fields ranging from industrial explosions and nuclear safety to supersonic combustors and to the development of combustion engines [1]. In explosive environments, hot jet ignition may take place due to a hot jet escaping from flameproof enclosures through inevitable gaps [2], e.g., like the ones present at the shaft bearing of an electri- cal motor. Closer analysis shows that hot jet igni- tion is a complicated process involving turbulent mixing of exhaust and fresh gas coupled with chemical reactions. It becomes even more complex at supersonic flow regimes when gas dynamic effects on the jet temperature can have a profound influence on the ignition process. The influence of pressure, temperature, and chemical kinetics on the ignition process has been examined widely for premixed H 2 /air mixtures [3]. The role of strain and turbulence has been studied for nonpre- mixed H 2 /air mixtures experimentally [4] and 1540-7489/$ - see front matter Ó 2006 The Combustion Institute. Published by Elsevier Inc. All rights reserved. doi:10.1016/j.proci.2006.08.027 * Corresponding author. Present address: German Aerospace Center (DLR), Institute of Combustion Technology, Pfaffenwaldring 38-40, D-70569 Stuttgart, Germany. Fax: +49 711 6862 578. E-mail address: Rajesh.Sadanandan@dlr.de (R. Sadanandan). Proceedings of the Combustion Institute 31 (2007) 719–726 www.elsevier.com/locate/proci Proceedings of the Combustion Institute