Abstract: Abstract: In order to study the fire extinguishing effect of liquid nitrogen in the utility tunnel, an experimental platform for liquid nitrogen fire extinguishing in a medium-sized utility tunnel was established. The fire extinguishing effect of liquid nitrogen was studied by analyzing the interaction between liquid nitrogen and flame after injection into utility tunnel and the changes of temperature and oxygen concentration near the fire source. The results show that the fire extinguishing process of liquid nitrogen is the result of cooling and inerting, inerting plays a leading role. At the same time, the greater the liquid nitrogen release distance, the longer the fire extinguishing time, the weaker the suppression effect of liquid nitrogen on the fire source and the stronger the gas disturbance in the flame area. The fire extinguishing efficiency of nitrogen injection at 0 m is 49% higher than that at 4 m. In addition, when the liquid nitrogen release distance is within a certain range, the fire extinguishing effect of vertical nitrogen injection is better than that of horizontal nitrogen injection. The fire extinguishing efficiency of vertical nitrogen injection is 18.7% higher than that of horizontal nitrogen injection at 0 m. With the increase of liquid nitrogen release distance, the difference between the two nitrogen injection methods gradually decreases. Therefore, accurate detection of fire source location and optimization of nitrogen injection mode can achieve the best fire extinguishing effect.

Key words: Key words: utility tunnel, liquid nitrogen fire extinguishing, nitrogen injection method, model experiment