纯电动和燃油公交车的火灾发展特性数值模拟研究

Numerical simulation study on fire development characteristics of pure electric and fuel buses

为了研究纯电动和燃油公交车火灾发展特性的异同,采用FDS数值模拟方法,考虑动力电池发生热失控喷射释放可燃气体并燃烧形成喷射火,对比电池包和燃油两类典型点火源下,公交车整车燃烧的热烟释放与火灾发展特性。结果表明:对于10.5 m长的纯电动和燃油公交车火灾,火灾增长速率均位于超快速火和快速火之间,在前500 s燃油公交车的热释放速率(Heat Release Rate,HRR)大于电动公交车,然而电动公交车HRR在500 s后大于燃油车;纯电动和燃油公交车峰值热释放速率(Peak Heat Release Rate,PHRR)分别为25.4 MW和24.2 MW,总热释放量(Total Heat Release,THR)分别为20.2 GJ和17.5 GJ,电动公交车相比燃油车具有更高的PHRR和THR,但PHRR达峰时间滞后144 s;在点火源距离后门较近和火灾前期100 s门窗均处于关闭状态最不利情况下,相比燃油公交车,电动车上部内饰的引燃时间提前、下部有所延迟,后天窗附近窗户破窗时间提前;在公交车火灾发展中,电动车窗户等开口部位处溢流火的高度大于燃油车,1 min内是人员逃生关键时间,且车厢内中后部温度均高于前部。

In this study,the FDS numerical simulation method was employed to investigate the similarities and differences in fire development characteristics between pure electric and fuel-powered buses.By considering the formation of jet fires resulting from the combustion of released combustible gas due to thermal runaway injection from power batteries,the study compared the heat and smoke release characteristics,as well as the fire development of buses under two typical ignition sources:the battery pack and fuel.In fire accidents involving pure electric and fuel buses with a length of 10.5 m,the fire growth rate falls between that of ultra-fast and fast fires.During the initial 500 s period,the Heat Release Rate(HRR)of the fuel bus surpasses that of the electric bus.Conversely,beyond 500 s,the electric bus exhibits a higher HRR compared to the fuel bus.The Peak Heat Release Rates(PHRR)for pure electric and fuel-powered buses are 25.4 MW and 24.2 MW,respectively,while their Total Heat Release(THR)values are 20.2 GJ and 17.5 GJ.These figures indicate that electric vehicles exhibit higher PHRR and THR compared to fuel-powered buses.Remarkably,the peak time of PHRR for electric vehicles occurs 144 s later than that of fuel-powered buses.In this paper,considering the most unfavorable scenario where the ignition source is close to the rear door and the doors and windows remain closed for 100 s in the initial stage of the fire,several notable differences are observed between electric and fuel buses.Compared to fuel buses,the ignition time of the upper interior of the electric vehicle is accelerated,while that of the lower part is delayed.Additionally,the time for breaking windows near the skylight is advanced in electric vehicles.Furthermore,during the progression of bus fires,the height of overflow fire at openings such as electric vehicle windows is greater than that of fuel vehicles.One minute represents a critical timeframe for people to escape,during which the temperature in the middle and rear sections of the compartment tends to be higher than that in the front.