Experimental Study On Smoke Properties In A Ship Room With Ceiling Vent

The "sealed effect" of a compartment decides the distinctive features of its fire. The compartment fire and its smoke have different processes due to the various building structure (shape, dimension), ventilation, and fuel type and so on. As a typical compartment in a ship, engine room usually does not have vertical openings (door and windows). The gas flow exchange at ceiling vents in this type of compartment would be determined by pressure and buoyancy, and has very complicated flow models, which would have a great influence on the smoke movement and distribution in the compartment. It is therefore very important that carrying on the research on the fire smoke development and distribution in the compartment with ceiling vent, to gain the knowledge of how the fire grows in such a compartment at different ventilation conditions and how to control the fire spread and rescue.Experimental studies were carried out in a compartment with dimensions of300cm (length)×300cm (width)×195cm (height). Ceiling vents with various sizes from100cm2(10cm×10cm) to3200cm2(54cm×60cm) were located at one corner of the ceiling. Heptane pool fires with diameter of10cm,14cm,20cm and30cm were adapted as fire source. In present study, the effects of opening size on the pool fire behavior were studied. Furthermore, the smoke density model together with the filling process of smoke in the enclosure is investigated. Then, based on the analysis of its characteristics, the fire smoke distribution in the ceiling vent compartment was predicted. The detailed work is as follows:Impacts of the ceiling vent and fire size on the fire development. The maximum temperature rise could be related to the fire size, and was higher when increasing the fire size. Under the condition in the current research, the average temperature rise rate was in proportion to the fire size. The ceiling vent size did not have significant impacts on the average temperature rise rate. When using the fuel mass loss rate as abscissa, the fire size did not affect the smoke density significantly, and the ceiling vent size did not impact smoke density in the early stage of the fire. In the experimental process, the distribution of the oxygen concentration was not uniform. The oxygen concentration was larger when the probe was closer to the floor, and the oxygen concentration in the fire zone was obviously larger than the rest space. In the ceiling vented compartment, the average fuel mass loss rate per area was closer to that of the boiling burning in the open space. With the increase of the pool size, the average fuel mass loss rate per area was gradually closer to that of the steady burning in the open space. The predicting model of smoke optics density in compartment fire with ceiling vent. The predicting methods of smoke optics density in ceiling vent compartment were analyzed based on macroscopic model of fire smoke. According to the mass conservation equation, K-S model, K-M model, Y-KS model and Y-KM model were built and their application was deeply discussed. The experimental results show that all the smoke density variations reconstructed by the four models were in good agreement with the experimental results in a certain degree. K-S model and Y-KS model are good for the qualitative analysis of fuel hazard in a standard compartment; the formula of K-M model and Y-KM model are uniform, and can provide good predictions of the smoke density at the early stage of the fire, given the fire and the ceiling vent size.The smoke filling process in the ceiling vent compartment based on the gas temperature and smoke optics density. The predicting methods of smoke filling time in ceiling vent compartment were analyzed based on physical model of smoke filling. According to the mass conservation equation and energy conservation equation,"expansion effect" model and "infinitely high ceiling" model were built. The predicted results from the models and the results obtained by light extinction coefficient method and subsection linear method from the experiments were compared."Expansion effect" model and "infinitely high ceiling" model could provide good predictions on smoke filling time in ceiling vented compartment fires. Under the current experimental conditions, the results indicated that the ceiling vent size did not have a significant impact on the smoke filling time in ceiling vented compartments, and the impact could be ignored when the HRR was larger enough.The predicting model of smoke distribution in the compartment During the fire smoke filling process in the compartment, the gas temperature trended to decrease with the height from top to the bottom, and showed a slope linear distribution. The smoke optics density also presented a process that the smoke went down from the top of the compartment, and almost became uniform until it filled the space above the fire flame. From the smoke distribution characteristics, the temperature and the smoke density distribution have been simplified and corresponding models for predicting these parameters based on "zone model" were established. By comparing the results from the model and experiments, it showed that these two models could provide good predictions for early stage fires in ceiling vented compartments. The use of the smoke distribution model was mainly restricted by the application range of the smoke temperature predicting model and the smoke density predicting model.