This paper built the experimental platform in the shrinkage-sized circular utility tunnel. A series of experiments were conducted by changing the parameters of liquid nitrogen injection. The feasibility of liquid nitrogen fire extinguishing in utility tunnel was studied. It is found that the main mechanism of liquid nitrogen fire extinguishing is cooling and asphyxiation. Cooling during vaporization can suppress fire rapidly, and the asphyxiation completely extinguishes the flame. During the liquid nitrogen fire extinguishing process, the temperature and the heat flux showed a decreasing trend of fast first and then slow. By increasing the injection rate and time of liquid nitrogen, the process of fire extinguishing can be accelerated and the extinguishing time would be shortened significantly. In addition, it is also found that the critical temperature at the flame of liquid nitrogen fire extinguishing is 230.0 °C, and the critical heat flux at 0.2 m from the flame is 0.20 kW/m². Not considering oxygen consumption and nitrogen leakage, the critical oxygen volume fraction of liquid nitrogen extinguishing cable fire in utility tunnel is about 15–16%.

本文在收缩规模的圆形公用工程隧道中搭建了实验平台。通过更改液氮注入参数进行了一系列实验。研究了公用隧道内液氮灭火的可行性。发现液氮灭火的主要机理是冷却和窒息。汽化过程中的冷却可以迅速抑制火势，窒息完全熄灭火焰。在液氮灭火过程中，温度和热通量呈先快后慢的下降趋势。通过增加液氮的注入速度和时间，可以加快灭火过程，并大大缩短灭火时间。此外，²。不考虑氧气消耗和氮气泄漏，公用事业隧道中液氮灭火电缆着火的临界氧气体积分数约为15-16％。