Current Issue : July - September Volume : 2020 Issue Number : 3 Articles : 5 Articles
This study investigates the continuous transition from flame-spreading to stabilized combustion near the blow-off limit in\nopposed forced flow by using expanding solid fuel duct that makes distribution of oxidizer velocity in the axial direction. The\nstabilized combustion is a diffusion flame that appears in the Axial-Injection End-Burning Hybrid Rocket. The boundary between\nflame-spreading and stabilized combustion has not been investigated in detail. Polymethyl methacrylate (PMMA) rectangular\nducts were used as a fuel, and gaseous oxygen was used as an oxidizer. All firing tests were conducted at atmospheric pressure. The\ndiffusion flame traveled in the opposed-flow field where the oxidizer velocity increases continuously in the upstream direction.\nThe combustion mode changed when oxidizer velocity at the flame tip exceeded a certain value. The oxidizer velocity used in this\nexperiment ranges from 0.6 to 32.8 m/s. Experimental results show that a threshold oxidizer velocity of the transition can be\ndetermined. In this study, the threshold velocity was 26.4 m/s....
Many experiments have been done by authors to study the influence of the natural ventilation through openings on fire behaviour\nin compartments. It has been revealed that fire will be influenced by the size of existing openings which can be an open window, an\nopen door, or both of them. Concerning the last case, the literature does not give any information about the impact of the\narrangement of these openings on the behaviour of fire......................
This work presents Large Eddy Simulations of the unconfined CORIA Rouen Spray Burner, fed with liquid n-heptane and air.\nTurbulent combustion modeling is based on the Filtered TAbulated Chemistry model for LES (F-TACLES) formalism, designed to\ncapture the propagation speed of turbulent stratified flames. Initially dedicated to gaseous combustion, the filtered flamelet model\nis challenged for the first time in a turbulent spray flame configuration. Two meshes are employed. The finest grid, where both\nflame thickness and wrinkling are resolved, aims to challenge the chemistry tabulation procedure. At the opposite the coarse mesh\ndoes not allow full resolution of the flame thickness and exhibits significant unresolved contributions of subgrid scale flame\nwrinkling. Both LES solutions are extensively compared against experimental data. For both nonreacting and reacting conditions,\nthe flow and spray aerodynamical properties are well captured by the two simulations. More interesting, the LES predicts\naccurately the flame lift-off height for both fine and coarse grid conditions. It confirms that the modeling methodology is able to\ncapture the filtered turbulent flame propagation speed in a two-phase flow environment and within grid conditions representative\nof practical applications. Differences, observed for the droplet temperature, seem related to the evaporation model assumptions....
The fuel staging combustion technology is a promising low NOx combustion\ntechnology for coal-fired boiler. In order to reduce NOx emissions, the burners\nof a 600 MWe coal-fired boiler are retrofitted in which methane gas is selected\nas a secondary fuel for re-combustion. The CFD models of combustion\nprocess are built to investigate effects of the methane gasratio on combustion\nprocess and NOx emissions. A total of 4 cases are numerically studied, including\nthe pure coal combustion case, the coal combustion with 7.5%, 10%,\n12.5% of methane gas re-combustion cases respectively. The results show that\nthe re-combustion of methane can reduce the temperature at primary combustion\nzone, but increase the temperatures at the re-combustion area and\nthe furnace outlet. The NOx concentration at the furnace outlet reduces with\nthe increasing methane gas ratio. Methane re-combustion can greatly benefit\nto the NOx emissions reduction....
Polymer combustion is an important factor in mine fires. Based on the actual environment in a mine tunnel, a cable combustion\nexperiment platform was established to study the regularities of the cable fire spread speed and smoke temperature under different\nconditions, including various fire loads and ventilation speeds. The flame change and molten dripping behaviour during the fire\nspread process were also analyzed. The experimental results show that the flame-retardant cable can be ignited and continuously\nburnt at a certain wind speed, but the combustion can be restrained at high wind speed. The combustion speed of the flameretardant\ncable is affected by the fire load and ventilation speed. The combustion droplets can change the shape of the flame, which\ncan consequently ignite other combustible materials. The analysis of the experimental results provides an important basis for the\nprevention of tunnel fires....
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