Elsevier

Combustion and Flame

Volume 164, February 2016, Pages 397-399
Combustion and Flame

Direct prediction of laminar burning velocity and quenching distance of hydrogen-air flames using an annular stepwise diverging tube (ASDT)

https://doi.org/10.1016/j.combustflame.2015.12.005Get rights and content

Abstract

Flame propagation characteristics of hydrogen-air mixtures were investigated using an improved annular stepwise diverging tube (ASDT). An infrared detectable camera was used to visualize flame behaviors. Flame propagation velocity (FPV) was examined using the variation of equivalence ratio (or premixing ratio) and flow rate. Conclusively, it was found that hydrogen-air flames have critical FPVs that are not significantly affected by the channel gap scales. The critical FPVs were measured over a range of equivalence ratio of 0.27 to 6.50, and the maximum critical FPV was approximately 285 cm/s at the equivalence ratio of 1.7. These values were comparable to the laminar burning velocities. Quenching distances were also measured using the identical ASDT system, and the minimum value was about 0.60 mm at approximately stoichiometric conditions.

Introduction

Laminar burning velocities (LBVs) and quenching distances have been used as fundamental data in combustion studies. A number of experimental results have been reported over the last century for various fuel-air mixtures and various methods. Recently, a series of state-of-the-art experimental methods based on an annular stepwise diverging tube (ASDT) have been invented and developed [1], [2], [3]. There were critical FPVs that were less affected by the channel gap scales. The critical FPVs were comparable to the LBVs for methane, propane, and dimethyl ether (DME). In addition, the quenching distances could be measured directly with the same burner.

To extend the applicability of the ASDT method, hydrogen-air premixed flames were investigated in this study because it is known that they have the highest LBV, the smallest quenching distance, and the widest range of flammability limits. First, the assembled ASDT system was improved to accommodate the significantly high LBVs and small quenching distances of hydrogen-air premixed flames. The existence and characteristics of the critical FPVs were investigated. The critical FPVs were compared to the LBVs of the hydrogen-air mixtures found in the literature. Quenching distances were also measured.

Section snippets

Results and discussion

The experimental setup is shown in Fig. 1a. The system consists of a quartz tube and a conically-shaped stepwise stainless-steel core. The stepwise core was assembled with 49 step-units that were aligned along a straight column. For hydrogen-air flames, far smaller channel gaps are required to measure higher FPVs and the quenching distances. Hydrogen (>99.999%) and dehumidified air at 296 ± 4 K were used. Their flow rates were regulated using several mass flow controllers after calibration. A

Acknowledgments

This work was supported by a National Research Foundation of Korea (NRF) Grant funded by the Korean government (MSIP) (NRF-2013R1A2A2A01015816). In addition, this work was also supported by the BK21 Plus Program.

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