Mechanism Study Of Deflagration Of Gasoline-air Mixture In Connected Compartments Of Shipping

Fire accidents on the ship increase greatly, causing a large number of casualties and property losses. There are numerous connected structures f ormed by cabins and corridors in the ship. Deflagration accident occurs in that kind of connected compartments is more destructive than the explosion in isolated compartment. Therefore, it is of theoretical and practical significance to study the deflagration in connected compartments for the safe operation of ships. For the deflagration phenomenon in connected compartments of a ship, this dissertation mainly investigates the effects of channel types, initial conditions and space scale on deflagration process, striving to obtain the mechanism of gasoline-air deflagration in connected compartments.Firstly, a three-dimensional mathematical model for unsteady gasoline-air deflagration in connected compartments was implemented, in which large eddy simulation and premixed combustion model are used. Numerical simulation results are compared with available experimental data. In addition to a slight difference in the time, the trend and the magnitude of deflagration parameters are in good agreement with the experimental data, verifying the validity of the model.Secondly, the influence of channel dimension and ignition position on deflagration, which occurs in connected compartments with equal volume, is investigated. Effect of channel length on deflagration intensity is small. In contrast, channel diameter has a strong effect on deflagration evolution. Under the condition of d=152mm, the intensity of deflagration is greatest and its rate of pressure rise is three time as fast as the condition of d=76mm. flame speed is accelerated with the increase of channel length and the decrease of channel diameter. Different ignition locations lead to changes of initial flame condition and initial flow field distribution, thereby deflagration process is affected, for example, when ignition is located in bottom of compartment, the intensity of deflagration is greater, with the overpressure up to 816 k Pa. Furthermore, the bend channel of the connected compartments results in more energy loss while flow and pressure propagati ng through it. Therefore, the deflagration intensity decreases.Thirdly, the effect of compartment volume ratio, channel dimensions and ignition position on deflagration, which occurs in connected compartment with unequal volume, is investigated. Deflagration evolution is strongly influenced by the compartment volume ratio, the length of the connecting channel and ignition position. With the increase of volume ratio, the degree of pre-compression becomes more effective and results in greater deflagration intensity wh en the primary ignition occurs in the larger of the two compartments, for example, when the volume ratio is 8, peak overpressure value is 941 k Pa and maximum rate of pressure rise is three times as fast as the condition of equal volume; Within certain range, the longer the channel length, the greater the intensity of deflagration; Compared to ignition in small compartment, the deflagration occurred in the larger compartment is more destructive with a 16.4% higher peak overpressure, a 2.5 times higher maximum rate of pressure rise.Furthermore, this paper studied the characteristics of deflagration occur s in large-scale connected compartments for equal volume and unequal volume. Like the small-scale situation, deflagrations propagating between large-scale connected compartments is characterized by pre-compression, jet flame and reverse flow. Also, the ratio of the volumes of the large-scale compartments is an important factor, which can lead to enhancements of deflagration. However, maximum overpressures and flame speed attained in large-scale space were higher than those in small-scale space. The process of deflagration in large-scale space takes a long time and its rates of pressure rise is higher.The above research work contributes to intensively understandi ng of deflagration phenomena in connected compartments and reveals the mutual coupling of flame, flow and pressure wave. This work not only gives guidance for ship safety, but also provides a reference for other industries including connected vessels.