Immersion liquid cooling is a thermal runaway protection strategy for lithium-ion batteries; however, the regulatory mechanism of immersion depth on battery thermal runaway remains unclear. In this study, 18650-type ternary lithium-ion batteries with capacities of 2000, 2600, and 3200 mAh were selected as research objects, and HFE-7200 dielectric fluorinated liquid was used as the cooling medium. A self-built immersion battery thermal runaway test platform was employed to investigate the influence of immersion depth on thermal runaway characteristic parameters. The kinetic laws of temperature variation, thermal runaway mass loss, and toxic gases, including CO, NO2, NH3, and HF, were discussed. The results show that immersion depth exerts a nonlinear regulatory effect on thermal runaway. Shallow immersion of 1–2 cm cools the lower part of the cell, prolongs the thermal runaway incubation time, and may intensify thermal runaway, whereas deep immersion of 3–4 cm can effectively suppress thermal runaway. When thermal runaway was effectively suppressed, the maximum system temperature was 264.3 °C. The average mass loss rates of the 2000, 2600, and 3200 mAh batteries under different immersion depths were 16.2%, 18.6%, and 38.8%, respectively. The release sequence of the four major toxic gases during battery thermal runaway was determined, and their peak concentrations were compared. A three-zone heat transfer model was established along the battery axial direction, clarifying that the proportional changes of the fully cooled zone, vapor-liquid coupling transition zone, and unimmersed runaway zone jointly govern the heat generation and heat transfer balance of the cell. This study can provide a quantitative experimental basis and theoretical support for safety liquid level calibration of immersion liquid cooling battery systems.
This study tested whether fine particulate matter (PM2.5) emissions from forest fuel combustion in the Xiao Xing’an Mountains are controlled by common or vegetation-category-specific factors. Six conifer, nine broad-leaved and seven shrub species were burned in a laboratory chamber (6966 measurements). Because the factors tested differed among categories, effects were analyzed within each category and compared across categories only for shared factors, using ANOVA, multiple linear regression, Random Forest and XGBoost. Fuel load was a primary factor in all three categories. In addition, PM2.5 was controlled by moisture content, plant part and combustion mode in shrubs; by plant part, season and species in broad-leaved species; and by plant part and wind speed in conifers. Among the shared factors, moisture content had a clear effect only in shrubs (partial η2 = 0.16 vs. ≤0.03 in trees). Smoldering tests produced 34% more PM2.5 than flaming tests in shrubs (p < 0.001), and broad-leaved bark and branches had 89% higher PM2.5 concentrations in April than in July. The mean shrub emission factor was 12.5 g/kg, without significant inter-species variation (p = 0.668). Under grouped five-fold cross-validation, Random Forest and XGBoost reached R2 of 0.77–0.96, compared with 0.21–0.74 for linear models. The results support vegetation category as a stratification variable in regional forest-fire emission inventories.
Wooden site cabins and modular units are combustible enclosures in which a single furniture fire can rapidly involve adjacent rooms, yet full-scale experimental data on multi-compartment fire development involving combustible interior linings remain scarce. This paper presents a full-scale fire experiment in a two-room wooden site cabin with combustible linings, supported by a simplified numerical investigation using the Fire Dynamics Simulator (FDS). An F21-type armchair, ignited using heptane as an accelerant in the corner of the fire room, served as the primary fire source. Temperature development was monitored using 19 thermocouples distributed across the compartments, doorways, and window. During the experiment, the fire developed rapidly from the armchair, reaching flashover in the primary room after approximately 2.5 min before spreading through the internal doorway into the adjacent compartment and subsequently causing window failure. The FDS model employed a simplified combustible-lining representation, with surface ignition at 340 °C and a prescribed heat release rate per unit area (HRRPUA) of 150 kW m−2. Following an empirically determined temporal alignment of 46 s, the simulation reproduced the general temperature development during the growth phase and early fully developed stage. The interval between the earliest flashover threshold crossings in the two rooms was 36 s experimentally and 24 s in the simulation, indicating a more rapid transition between compartments in the model. This difference may partly reflect the simplified treatment of combustible surface ignition and fire spread. However, the temporal alignment and simplified modelling assumptions limit conclusions regarding independent predictive accuracy, particularly for event timing and later-stage temperature development. The primary contribution is a full-scale experimental reference case for investigating fire development and spread in lightweight, combustible multi-compartment structures. The experimental data and supporting numerical materials are openly available through Zenodo, facilitating further model assessment and research.
To investigate fire-induced smoke transport in continuous inclined evacuation passages of deep-buried metro stations, a 1:15 reduced-scale model was constructed according to the Froude similarity criterion. Experiments were conducted using nominal fire source powers of 3, 8, and 13 kW under different ventilation conditions and passage configurations. Without ventilation, the smoke-front arrival time at the outlet of the fourth inclined section decreased from 385 s at 3 kW to 35 s at 13 kW. Increasing fire source power also increased the temperature difference between the ceiling and the representative occupant height. Natural ventilation reduced temperatures near the fire source but caused smoke to reach downstream sections earlier. Under the 13 kW condition, temperatures at the remote measurement point increased under natural ventilation. Increasing the number of passage sections delayed smoke arrival at the passage end under the 3 kW condition, whereas the effect was limited at 13 kW. These findings provide experimental data for smoke-control design and evacuation safety assessment in deep-buried metro stations.
To address the challenge of quantitatively coupling fire smoke evolution and occupant evacuation in the underground powerhouses of large-scale pumped-storage power stations, full-scale three-dimensional numerical models were developed using PyroSim for fire dynamics and Pathfinder for egress behavior. A multi-factor coupled ASET–RSET safety margin matrix was constructed, integrating fire heat release rate (HRR), sprinkler intervention, egress passage blockage, and occupant load. The results show that visibility continuously dropping below 10 m at a characteristic hazardous height of 4.5 m serves as the governing criterion determining the available safe egress time (ASET). Under a 10 MW fire without sprinklers, the ASET is 343.0 s, whereas activating the sprinkler system effectively suppresses smoke and reduces temperatures, extending the ASET to 380.9 s. With both exits unobstructed, the required safe egress time (RSET) for the baseline 130 occupants is 303 s and increases marginally to only 304 s as the crowd scales to 250 occupants, thereby maintaining a positive safety margin under all scenarios. Conversely, the blockage of a single-sided passage induces a pronounced bottleneck shift. Specifically, blockage of the main access tunnel exhibits acute sensitivity to crowd enlargement: the RSET surges to 441.8 s for 250 occupants, resulting in a severe safety margin deficit that cannot be fully rectified even with sprinkler intervention. Accordingly, two distinct risk boundaries—management-sensitive and structure-constrained regimes—are identified. An optimal egress routing scheme characterized by “hierarchical zoning, lateral priority, and nearest-ascending egress” is proposed, accompanied by a two-dimensional cooperative prevention and control strategy: “source control to delay ASET and capacity expansion to reduce RSET.” This work provides quantitative support for performance-based fire safety design and emergency management in deep-buried underground powerhouses.
