Natural Ventilation of Removing Air Pollutants in Long Railway Tunnels with Diesel Traction on Lhasa-Rikaza Line of China

Diesel traction Locomotives are widely used in railway tunnels in the plateau of China. Harmful gases given out by internal combustion engines must be excluded from the tunnel for human safety on railway. In the present study, nitrogen dioxide (NO₂) was taken into account as a representative harmful pollutant of the investigation object. Natural ventilation of diluting the concentration of NO₂ pollutant in the long railway tunnels was discussed according to real engineering on Lhasa-Rikaze line of China. One-dimensional unsteady flow models of tunnel ventilation were set up. The transient differential equations of the air velocity in the tunnel were solved by Runge-Kutta method and discrete convection-diffusion equations of scalar NO₂ concentration were discretized by controlling volume method and solved by first order upwind scheme. Cases with and without service gallery were discussed in terms of piston wind speed and elapsed time of diluting NO₂ concentration. Both positive and negative winds were considered. Based on the feasibility analysis of natural ventilation conditions, it is suggested that natural ventilation can settle for diluting harmful gases in tunnels with tunnel length less than 3 km on Lhasa-Rikaze line. Whereas the tunnel length is larger than 3 km, piecemeal natural ventilation with service gallery isn´t recommended because it can´t efficiently shorten the time of removing pollutants.