Experimental study of flame geometry of flame spread in a moving body under forced flow in a long and narrow confined space

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The physical appearance of a flame in a long and narrow confined space, such as a tunnel, is an important factor in determining the development of flame spread in moving bodies and the distribution of the energy field in space. A thermally thin fuel flame spread experiment was carried out in a reduced-size experiment platform. Two types of wind flow conditions were considered, i.e., wind flow field caused by piston effect only and wind flow field caused by longitudinal ventilation system and piston effect. Based on the piston wind calculation model developed by the previous authors, a simplified forced wind flow calculation formula was constructed, and the predicted values were in good agreement with the measured values. An improved image processing method was utilized to quantitatively describe the changes in the geometric features of the flame during the flame spread process. The flame probability plot shows that the characteristic flame tilt angle shows an overall increasing trend with the increase of forced wind flow. The flame height fluctuates within a certain range under the condition of forced flow less than 1.0 m s-1, and decreases with the increase of moving body velocity and longitudinal ventilation wind speed under the remaining conditions. Finally, based on the previous prediction model of flame tilt during moving fire source and flame spread, the prediction model of flame tilt under lateral flame spread condition for a moving body in a narrow and long confined space is constructed by introducing the velocity factor, and the error is within 20 % in the case of downstream flow.