为探究火源位置对送风环境下地铁车厢火灾探测器响应时间的影响,研究了不同火源位置下车厢内烟气蔓延规律及探测器响应时间。研究结果表明:回风口处风速较大,如果火灾发生在回风口附近,烟气可能会通过回风口进入车厢顶部送风系统,进而无法及时蔓延进入车厢顶部C形槽中,从而可能导致探测器响应时间延长。较大的风速会阻碍烟气向车厢顶部的蔓延,从而导致烟气无法快速进入C形槽内,致使探测器响应时间延长。因此,送风口所在截面的位置相比于车厢中心截面是更不利于火灾探测的位置。对该研究建立的车厢模型来说,在C形槽内布置2个探测器较为合理,在该研究设定的各火灾场景下,探测器均可在60 s内探测到烟气。该研究结果可为此类地铁车厢的探测器布置提供参考。
[Objective] Currently, many achievements in the study of subway car fires are mainly concentrated on the full development stage of fires. However, in-depth research on early fire detection and improving detection efficiency is limited. Further research is necessary on the response time of fire detectors in subway car fire incidents, considering the influence of the air conditioning system.[Methods] To investigate the influence of fire source location on the response time of fire detectors in subway cars under an air supply environment, this study examines the smoke spread patterns and detector response times in cars with different fire source locations. Using an actual subway car as the basis, a simulation model of the car is created. In this model, air is uniformly supplied downward through the air supply port at the top of the car, while return air flows through ports at the top of the car. The passenger area contains seats, and the top of the car features four return air outlets and four waste exhaust outlets that are symmetrically arranged. The boundary conditions of the car air conditioning system mainly consist of supply air, return air, and waste exhaust boundaries. The total air intake of the whole car is 10 000 m3/h, the total waste displacement is 3 850 m3/h, and the total return air volume is 6 150 m3/h.[Results] In the fire detection experiment, the location of the fire source directly below the air supply port on the top of the car is more affected by airflow and is the most unfavorable detection position for fire detectors compared with the locations between the two air supply ports. The velocity is larger at the return air outlet. If a fire occurs near the return air outlet, smoke may enter the air supply system at the top of the car through the return air outlet. In this case, the fire cannot spread into the C-slot in time, which may prolong the detector response time. Higher wind speeds will prevent the smoke from spreading to the top of the car, thus preventing the smoke from entering the C-slot quickly enough to reach the fire detectors. Therefore, the location of the cross-section where the air supply outlet is located is less favorable for fire detection than the cross-section in the center of the car.[Conclusions] For the subway car modeled in this study, placing two detectors in the C-slot is relatively reasonable because they can detect smoke within 60 s in all the fire scenarios considered. The findings provide insights into detector placement in subway cars, aiding in enhancing fire detection strategies.
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