Study on the Length of Smoke Backlayering of Double-Source Fire in Tunnels.

In order to predict the smoke backlayering length of double-source fire in tunnels, this paper deduced the dimensional expressions for smoke backlayering length by theoretical analysis and proposed a prediction formula for smoke backlayering length in single-source fire on the basis of the Fire Dynamics Simulator. Based on the results, the paper proposed a method for studying the smoke backlayering length of double-source fire in the tunnel. By introducing the fire power influence coefficient α and the distance influence coefficient ß, the formula for predicting smoke backlayering length in single-source fire was revised to obtain a new formula for predicting the smoke backlayering length of double-source fire. By comparing the formula prediction value with the simulation value, it is found that the prediction formula is almost accurate. This study will be helpful for understanding the multisource tunnel fire and predicting the smoke backlayering length of double-source fire in tunnels, which can provide guidance for tunnel fire rescue.

Coupling Relation between the Location of Cross-Cut Negative Pressure and Injecting Nitrogen into Coal Mine Goaf.

Injecting nitrogen into goaf has been widely adopted for preventing fire hazards in coal mines. In this paper, the coupling relation between different locations of negative pressure of cross-cut drainage and nitrogen injection was investigated. The minefield data collection was carried out by an in situ beam tube system on the intake airway and return airway of the mine goaf. The validated Computational Fluid Dynamics (CFD) model that was secondarily modified by on-site collected data was applied for further research. It is demonstrated that the area of the spontaneous combustion zone generally shows a sharp decline first, then tends to stabilize, and finally has a slight drop and rise with the increasing nitrogen injection time. It is obvious that the location of the negative pressure of cross-cut exerts a significant influence on the optimal nitrogen injection location and time. When the cross-cut is located in the center of the air leakage zone, spontaneous combustion zone, and asphyxiation zone of goaf, the optimal nitrogen injection location and time correspond to the P2 (25 m, 1200 min), P3 (30 m, 120 min), and P4 (35m, 1800 min), respectively. According to the simulation result, the specific relation between the optimal nitrogen injection point N(x) and the distance from the working distance of the cross-cut (x) by Newton interpolation polynomial analysis was figured out and verified that N(x) = 24.70808 + 0.293356x - 0.001436x 2. It is hoped that the result can provide scientific guidance for coal mine fire prevention and control with nitrogen injection.

Reaction Mechanism of Aldehyde Groups during Coal Self-Heating.

In order to further understand the mechanism of coal self-heating in the initial stage, the aldehyde group was analyzed by using the quantum chemistry methods. The charge distribution, structural parameters, and molecular orbital were analyzed to determine the active sites existing in the structure of aldehyde group. Then, a chemical reaction model including five elementary reaction sequences was established. In elementary reaction E1, the hydrogen of the aldehyde group is captured by hydroxyl to form the aldehyde radical, which provides the reactant and accumulates heat for the subsequent reaction. In elementary reaction E2, the aldehyde radical further reacts to form a carbon-free radical (R·) and CO, which is the main source for CO generation during coal spontaneous combustion. In elementary reaction E3, the aldehyde radical is oxidized to a carboxyl radical, providing the reactant for elementary reaction E4, which is directly related to CO2 generation during coal spontaneous combustion. The thermodynamic parameters of the elementary reactions were further analyzed and confirmed by quantum chemistry methods. The results are helpful for further understanding the pathways of CO generation in the initial stage of coal spontaneous combustion, which provides theoretical support for prediction of coal spontaneous combustion.