Inﬂuences of the Initial Ignition Energy on Methane Explosion in a Flame Deﬂagration Tube Mohammed J. Ajrash, † Jafar Zanganeh,* ,† and Behdad Moghtaderi † † The Frontier Energy Technologies Centre, Chemical Engineering, School of Engineering, Faculty of Engineering & Built Environment, University of Newcastle, Callaghan, NSW 2308, Australia ABSTRACT: It was observed that the initial ignition energy inﬂuences the ﬂame deﬂagration characteristics of methane explosions. This distinct behavior has been noticed by a number of scholars, and in our laboratory scale explosion chamber recently. However, the ﬂame traveling behavior has not been adequately clariﬁed in industrial scale ﬂame deﬂagration tube (FDT). This experimental work investigates methane ﬂame deﬂagration and varied initial ignition in a large scale FDT (30 m long) facilitated at University of Newcastle, Australia, to comprehensively investigate methane ﬂame deﬂagration behavior. The initial ignition energy was delivered by three alternative chemical ignitors’ energies, which were 1, 5, and 10 kJ. The results of the study revealed the notable inﬂuences of the initial ignition energies on the ﬂame deﬂagrations, over pressure rises, and pressure wave velocities along the FDT. When the initial ignition energy was increased from 1 kJ to 10 kJ, the maximum over pressure rises increased by 45% and 56%, respectively, for the 7.5% and 9.5% methane concentrations. For a 9.5% methane concentration, the increased ignition energy enhanced the pressure wave velocity from 130 m·s -1 to 359 m·s -1 and enhanced the ﬂame deﬂagration velocity from 105 m·s -1 to 179 m·s -1 . 1. INTRODUCTION The hazards of methane explosions and ﬂame deﬂagrations still represent a threat for chemical plants, mining tunnels, pipes, and other extractive and processing concerns. Accidental ﬁres in the process industries can cause enormous losses in life and capital. 1-4 One of the challenges is to eliminate and reduce the consequences of accidental ﬁres and explosions in pipes. To achieve that goal, accurate data concerning large scale setups is required to understand the characteristics of methane explosions in pipes. 5 The hazards of gas explosions in pipes was ﬁrst highlighted in the last century by a number of scholars. 6,7 They observed that the pressure in a tube develops and eventually leads to a rapid pressure rise, commonly termed a detonation. The properties of methane ﬂame deﬂagration in pipes were ﬁrst investigated by Mason and Wheele. 8,9 They used a 5 m long laboratory scale tube of 20 mm diameter. They noticed that the ﬂame deﬂagration velocity increases as the ﬂame reaches the end of the tube. Phylaktou (1990) 10 investigated methane explosions and the resultant ﬂame deﬂagrations in a vertical laboratory scale pipe. He found that the pressure rise may reach 6.9 bar at some point during the ﬂame deﬂagration. Additionally, he observed that the ﬂame does not deﬂagrate at a constant velocity. 10 In a 30 m detonation tube, the behaviors of static and dynamic pressures were examined as functions of the methane volume. 11 The goal was achieved by using a varied length per diameter ratio (L/D) of FDT. The authors claimed that the methane volume had no eﬀect on the static and dynamic pressures when the tube was open at one end. Qingzhao et al. 12 used a closed laboratory scale explosion tube to investigate the characteristics of 9.5% methane explosions ignited by a 10 kJ initial ignition energy (IIE). The authors observed that the reﬂected pressure wave could rupture and extinguish the ﬂame. Another series of large scale detonation tube experiments have previously been conducted to address the locations and properties of methane explosions, which eventually end up as detonation phenomena. 13-22 Other scholars have investigated the inﬂuences of other factors on methane ignition and ﬂame propagation, such as the initial conditions. 23-25 A number of researchers have highlighted explosion characteristics and the eﬀects of IIE on the ﬂammability limit of methane. Zabetakis et al. 26 tabulated the ﬂammability limits of methane at atmospheric conditions. The results were based on a small scale experimental setup. Hertzberg et al. 27 used a 20 L (liter) explosion vessel to investigate the ﬂammability limits and pressure rise rates of methane under variable IIEs. Herzberg et al. concluded that the pressure rise of a methane explosion (at the stoichiometric air concentration) initiated by high IIE is lower than the explosion initiated by a low IIE. 27 Cashdollar et al. 28 used 20 and 120 L explosion vessels to thoroughly analyze the ﬂammability limits of methane and other hydrocarbon gases. The scholars proved that the IIE could extend the methane and hydrocarbon gas ﬂammability limits. Bai et al. 29 studied the ﬂame deﬂagration and pressure proﬁles of methane and a hybrid mixture (methane-coal dust) employed in a 10 m 3 cylindrical explosion chamber (3.5 m long, 2 m diameter). The ﬁndings for the methane air mixture showed that the 40 mJ ignitor limited the methane ignition by between 5% and 13%, and limited the maximum pressure rise to between 5% and 13%, at a distance according to the methane concentration. The duration of the ignition spark has been explored by Zhang et al., 30 who employed 5 and 20 L explosion vessels to discuss the inﬂuence of explosion chamber volume on explosion characteristics. The authors showed that the explosion characteristics are slightly Received: December 22, 2016 Revised: April 30, 2017 Published: May 1, 2017 Article pubs.acs.org/EF © XXXX American Chemical Society A DOI: 10.1021/acs.energyfuels.6b03375 Energy Fuels XXXX, XXX, XXX-XXX