Flame propagation in a layered flammable gas mixture along the fuel-spilled ground was studied experimentally. The behavior of flame tip was investigated by simultaneous measurements of the images by color Schlieren photography and by chemiluminescence zone due to OH radical in the flame tip. The effects of ground conditions; the surface inclination, the ground temperature and the counter airflow velocity, on the propagation velocity of flame tip and on the thickness of flammable gas layer were examined. The thickness and the length of OH luminescence zone in the flame tip were in the order of 1 and 2～3 cm respectively. The tip of OH luminescence zone propagates in the velocity boundary layer of the counter airflow along the fuel-spilled ground. When the ground temperature is not so high, even over the stoichiometric temperature of the liquid fuel, no propagation of flame tip occurs in the counter airflow of which the velocity is over the flame propagation velocity without the airflow. This is mainly due to the decrease in the rate of formation of flammable gas layer on the unburned ground, which is in contrast to the flame propagation along the liquid pool surface in an opposing airflow.
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