As a highly effective and environmentally benign suppression agent, liquid nitrogen (LN2) has been widely used for fire extinguishing in plants, dwellings, enclosed underground tunnels, and other confined spaces through cooling and inerting. It is of great significance to understand the cooling and inerting effects of LN2 injected into a confined space. A confined-space experimental platform was developed to study the injecting LN2 into the platform with different injection parameters, such as mass flux, pipe diameter, and inclination angle. In addition, a mathematical model of quantitatively assessing cooling and inerting effects was proposed by using heat transfer capacity, inerting coefficient, and cooling rate. Results showed that the inerting effect was gradually enhanced with a mass flux increasing from 0.014 to 0.026 kg/s and then tended to level off; an appropriate pipe diameter of 12 mm was optimal for the cooling and inerting effects in this experiment. In addition, a positively increasing inclination angle could contribute to the cooling and inerting effects. However, there was little effect on the cooling and inerting with an inclination angle less than 0°. This study can provide technical guidances for environmentally friendly fire extinguishing with LN2 in a confined space.

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Heat release of coal combustion in an oxygen-lean and multi-gas environment is a common phenomenon, coalfield fires caused by it can lead to serious environmental destruction and loss of coal resources. Simultaneous thermal analysis experiments for Bulianta (BLT, high-volatile bituminous coal) and Yuwu coal (YW, anthracite) in 21vol.%O2/79vol.%N2 and 15vol.%O2/5vol.%CO2/80vol.%N2 were carried out to study the law of heat release. Based on the TG-DTG-DSC curves, the combustion characteristic parameters were analyzed. Decreasing O2 concentration caused a significant reduction of local reactivity and further the decreasing maximum heat release rate for low-rank coal, while increasing CO2 concentration caused a significant thermal lag effect and further the increasing maximum heat release rate for high-rank coal. The relationship between the heat release rate and the reaction rate constant was quantitatively analyzed. At the increasing stage of the heat release rate, the heat release rate of the two coals increased conforming to ExpGro1 exponential model. At the decreasing stage of the heat release rate, the heat release rate of YW coal decreased exponentially with the reaction rate constant, while the heat release rate of BLT coal decreased linearly. Regardless of the atmospheres, the conversion rates corresponding to maximum heat release rate of BLT and YW coal were about 0.80 and 0.50, respectively, indicating that the coal rank played a dominant role. The results are helpful to understand the heat release process of coal oxygen-lean combustion in O2/CO2/N2.