Premixed CH4-Air Flame Structure Characteristic and Flow Behavior Induced by Obstacle in an Open Duct

Dengke Li,Xianfeng Chen,Ali Rangwala,Ying Zhang

doi:10.1155/2014/248279

Dengke Li, Xianfeng Chen + Show 2 more

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https://doi.org/10.1155/2014/248279

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Abstract

To study the fuel gas combustion hazards, the methane/air flame structure and flow characteristic in an open duct influenced by a rectangular obstacle were explored by experiment and realizable k-∊ model (RKE). In the test, the high-speed schlieren photography technology and dynamic detection technology were applied to record the flame propagation behavior. Meanwhile, the interaction between flame front and flame flow field induced by the obstacle was disclosed. In addition, the laminar-turbulence transition was also taken into consideration. The RKE and eddy dissipation concept (EDC) premixed combustion model were applied to obtain an insight into the phenomenon of flow change and wrinkle appearing, which potently explained the experimental observations. As a result, the obstacle blocked the laminar flame propagation velocity and increased pressure a little in an open duct. Some small-scale vortices began to appear near the obstacle, mainly due to Kelvin-Helmholtz instability (KHI), and gradually grew into large-scale vortices, which led to laminar-turbulent transition directly. The vortices thickened the reaction area and hastened the reaction rate; reversely, the higher reaction rate induced larger vortices. The RKE model result fitted the test data well and explained the wrinkle forming mechanism of two special vortices in the case.

Highlights

As an important alternative energy, natural gas was more and more widely used in combustion field and power system
Gas explosive intensity was mainly laid on the flame propagation velocity; flame acceleration characteristic usually became a focus of gas explosion study
In order to acquire the flame propagation characters, the experimental set-up was schematically shown in Figure 1, which was composed of a semivented explosive pipe, a gas mixing system, an electrode ignition system, a synchronous control system, a data acquisition station (DAS), and a high-speed schlieren and camera system

Summary

Introduction

As an important alternative energy, natural gas was more and more widely used in combustion field and power system. Incident statistics data of fires and explosions showed that flammable gas was involved in 90% of the total accidents, which was one of the most destructive accidents in industry and living field. Numerous industrial incidents showed that the gas explosions were usually induced by faint ignition. Flame propagation velocity was small enough at the beginning of the explosion, environment conditions and some external factors may accelerate flame propagation and enhance explosion intensity greatly [1,2,3]. Gas explosive intensity was mainly laid on the flame propagation velocity; flame acceleration characteristic usually became a focus of gas explosion study. For example, in complex plants, the premixed flame propagating away from an ignition source may encounter obstacles with various shapes and boundaries along the path.

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