The combined effect of a water mist system and longitudinal ventilation on the fire and smoke dynamics in a tunnel

The individual and combined effect of a water mist system (WMS) longitudinal ventilation (LV) on the fire HRR, smoke temperature back-layering (BL) degree were explored in 3 m (width)×2.2 m(height)×30 (length) tunnel model. A series 39 tests has been conducted 6 configurations, varying velocity, volume flow rate nozzles arrangement. When WMS or LV is imposed individually, reduction HRR gets stronger with larger rates higher velocities. Yet, under effect, velocity non-monotonic: first reduces more, then rises again velocities for given settings. monotonically increases velocities, contrast to behavior. above phenomenon explained be due relatively ‘low’ flame height present paper, as consequence which interaction between droplets mainly occurs lower part tunnel, while hot happens upper part. behavior relates part, depends both regions. Besides, certain BL distance, required reduce by 13%–55% activated WMS, compared same conditions without WMS. covering shield also discussed. For small distance are place.