Investigation of smoke dispersion characteristics of battery electric vehicle fires in longitudinally ventilated, steep-slope, small-radius mountain tunnels

This study numerically explores smoke dispersion in mountain tunnels with large slopes and small radii during battery electric vehicle fires, using FDS to create 42 scenarios that combine slope, curvature, and longitudinal ventilation. Results reveal strong interactions among these factors: a steeper slope enhances the chimney effect, speeding up smoke movement, while smaller radii intensify local heat buildup and confinement, leading to nonlinear changes in maximum ceiling temperature. Based on these findings, a unified model for predicting maximum roof temperature, adjusted formulas for longitudinal temperature decay, and combined correction factors for critical ventilation velocity are proposed, all showing high accuracy and practical relevance. The study enhances understanding of smoke behaviour in complex tunnels and offers quantitative insights for ventilation design, hazard evaluation, and emergency smoke-control strategies in electric-vehicle fire scenarios.