城市地下综合管廊做到了地下空间的综合利用和资源共享，也是未来的一个发展趋势。然而，综合管廊火灾救援与普通交通隧道火灾救援有明显的差异。当天然气管道舱及容纳电力电缆舱室等发生火灾时，通常进行区段防火分隔，可采用封闭注氮的技术措施进行灭火。因此，研究封闭状态注氮控灭对综合管廊火灾演变的影响规律，将对综合管廊火灾救援具有重要的理论指导意义。 
结合城市地下综合管廊火灾的特点，基于Froude相似准则，设计搭建尺寸比例1:3的综合管廊火灾模拟实验台，考虑火源功率、注氮位置和注氮压力等因素，进行了注氮对封闭管廊火灾熄灭特性的影响规律实验研究，得到了氮气油池燃料质量损失速率峰值与注氮流量成反比关系；封闭管廊内火源燃烧的火焰相比自然通风环境中的明显减小，甲醇燃烧火焰颜色表现为近橙红色；在燃料燃烧的衰退期，火焰在油池表面上会变成游离态；综合管廊内火灾发生熄灭的氧气浓度范围为11.13~14.98%。建立了适用于封闭状态下综合管廊空间注氮过程火灾熄灭时间预测模型。
利用锥形量热仪和热分析联用实验，开展了综合管廊内典型阻燃电缆燃烧特性实验，研究了综合管廊电力舱内典型的ZRC-YJV22 8.7/15KV 3×50mm2阻燃电缆的燃烧特性及热解行为，得到了其主要热解反应各阶段的动力学参数，构建了封闭管廊电缆蔓延火灾注氮控灭数值计算模型；通过综合分析和数值模拟结果，发现综合管廊内的火灾烟气相比常规隧道更易沉降；液氮具有冷却降温与隔氧窒息特点，可快速降低火场温度和氧气浓度，降低了管廊内电缆受火灾余温作用发生短暂回燃复燃概率，有效控制封闭管廊火灾规模和发展程度，实现快速有效地火灾扑救；注氮控灭时封闭管廊内顶棚温度衰减可近似采用双指数经验预测模型来表征，但受液氮的冷却降温与隔氧窒息的耦合作用影响，该模型在各时间段有明显差异。

Urban utility tunnel achieves comprehensive utilization and resource sharing of underground space, which is a development trend in the future. However, there are obvious differences between fire rescue in urban utility tunnel and ordinary traffic tunnels. When a fire occurs in the urban utility tunnel such as the gas pipeline cabin and the power cable cabin, the section fire separation is usually carried out, and the technical measures of closed nitrogen injection can be used to extinguish the fire. Therefore, studying the effect of nitrogen injection and control and extinguishing in the closed state on the fire evolution of the urban utility tunnel will have important theoretical guiding significance for the fire rescue of the urban utility tunnel.
Combined with the characteristics of urban utility tunnel fires, and based on the Froude similarity criterion, the urban utility tunnel fire simulation test bench with a size ratio of 1:3 was designed and built. Considering factors such as fire source power, nitrogen injection location and nitrogen injection pressure were carried out. The experimental study on the influence of the fire extinguishing characteristics of the closed urban utility tunnel shows that the peak fuel mass loss rate in the oil pool is inversely proportional to the nitrogen injection flow rate. The color of methanol combustion flame is nearly orange-red. In the decay period of fuel combustion, the flame will become free on the surface of the oil pool. The oxygen concentration range of the fire extinguished in the urban utility tunnel is 11.13~14.98%. A prediction model of fire self-extinguishing time suitable for nitrogen injection in urban utility tunnel under closed state is established.
Through the cone calorimeter and the quadruple analysis system, a series of experiments on the combustion characteristics of 8.7/15KV 3×50mm2 flame-retardant cable in the urban utility tunnel were carried out. Combustion characteristics and pyrolysis behavior of the cable were analyzed. The heat release rate, combustion products, ignition characteristics and cable pyrolysis reaction of cable wrapping materials of the cable were quantitatively analyzed. Based on these, a numerical calculation model for nitrogen injection control and extinguishing of the cable spread in a closed urban utility tunnel was constructed. Through theoretical analysis combined with numerical simulation analysis, it is found that the fire smoke in the urban utility tunnel is easier to settle than the conventional tunnel. Liquid nitrogen has the characteristics of cooling and oxygen insulation, which can quickly reduce the temperature and oxygen concentration of the fire site, and reduce the occurrence of the residual temperature of the cable in the urban utility tunnel. The probability of short-term re-ignition and re-ignition can effectively control the scale and development of the fire in the closed urban utility tunnel, and achieve fast and effective fighting fire. The temperature decay of the ceiling in the closed urban utility tunnel can be approximated by a double-exponential empirical prediction model when nitrogen injection is controlled and extinguished. However, the double-exponential empirical prediction model of the ceiling temperature decay in the closed urban utility tunnel has obvious differences in each time period.

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