Full Length Article Effectiveness of diluent gases on hydrogen ﬂame propagation in tee pipe (part II) – Inﬂuence of tee junction position Sina Davazdah Emami a,b,c , Raﬁziana Md. Kasmani b,⇑ , Zahra Naserzadeh c , Che Rosmani Che Hassan a , Mahar Diana Hamid a , Siti Zubaidah Sulaiman d , Norazana Ibrahim b , Mohd Dinie Muhaimin Samsudin b a Chemical Engineering Department, Faculty of Engineering, University of Malaya, 50603 UM Kuala Lumpur, Malaysia b Clean and Efﬁcient Energy Research, Department of Energy Engineering, Faculty of Chemical and Energy Engineering, Universiti Teknologi Malaysia, 81310 Skudai, Johor, Malaysia c Industrial Safety Department, Faculty of Engineering, Kar Higher Education Institute of Qazvin, 3431849689 Alvand, Qazvin, Iran d Faculty of Chemical and Natural Resources Engineering, Universiti Malaysia Pahang, 26300 Kuantan, Pahang, Malaysia highlights  The ﬂame ﬂow mechanism inside the symmetric and asymmetric tee pipe conﬁgurations.  Effects of ignition position on ﬂame acceleration of fuels.  Dynamic of ﬂame acceleration of hydrogen-inhibitors/air mixtures.  Inﬂuence of obstacle location on ﬂame development of hydrogen-inhibitors/air mixtures. article info Article history: Received 26 May 2016 Received in revised form 31 October 2016 Accepted 3 November 2016 Available online 9 November 2016 Keywords: Explosion severity Hydrogen Diluents Obstacles Tee pipes abstract Gas explosions in obstructed vessels have been investigated for many years. However, the ﬂame acceler- ation mechanism of enriched-hydrogen fuels with diluents in the piping system has received little sys- tematic study in the literature. This particular study aimed to analyse the ﬂame front mechanism of hydrogen-diluents/air explosion inside the pipe by considering the inﬂuence of tee junction distance from the ignition points. The tests were performed using H 2 /diluents-air at different concentrations and ignition positions, in two different tee junction pipe conﬁgurations. From the results, the worst case of explosion severity was found in 95% H 2 –2.5% Ar–2.5% N 2 /air for all ignition positions. In general, if igni- tion happened at the tee junction, the overpressure and rate of pressure rise proﬁles showed almost a similar trend on both conﬁgurations. Similar trend was also observed for the ﬂame ﬂow characteristic analysis. Overall, it was clearly demonstrated that a shorter distance between ignition point and obstacles resulted in higher explosion severity. Ó 2016 Elsevier Ltd. All rights reserved. 1. Introduction Nowadays, the need for energy is soaring signiﬁcantly in respect of conventional energies. Amongst all sources of energy, hydrogen is promising for the future due to its cleanliness, efﬁciency and renewable capability, while it is appropriate to characterize the combustion behaviour of hydrogen-air mixtures for the purpose of both safety and engineering applications of combustion [1]. However, incidents involving hydrogen fuels and pipeline explo- sions resulting in injuries, fatalities, destruction of equipment and downtime remain a signiﬁcant problem in the process industry. As a consequence, there is a need in numerous synthetic procedures for assurance against proliferation of undesirable igni- tion marvels, for example, deﬂagration to detonation (DDT) in pro- cess equipment or piping and vent complex systems [2]. Among all precaution methods, inerting system has been considered as a suit- able and reliable method for reducing the probability of ﬂammable material combustion, especially hydrocarbon components, by using a chemically non-reactive gases (diluents) such as nitrogen, argon and carbon dioxide [3]. However, as far as authors’ knowledge, only scarce and limited data available in literature on the effect of diluents on hydrogen explosion behaviour for different systems. For instance, Kwon and Faeth [4] investigated the effects of N 2 , Ar or He on the laminar burning velocities of H 2 -O 2 ﬂames, both experimentally and by computer modelling. Their results indicated http://dx.doi.org/10.1016/j.fuel.2016.11.018 0016-2361/Ó 2016 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail addresses: sinadavazdahemami@gmail.com (S.D. Emami), raﬁziana@utm. my (R.Md. Kasmani). Fuel 190 (2017) 260–267 Contents lists available at ScienceDirect Fuel journal homepage: www.elsevier.com/locate/fuel