The Limits For Installing Mechanical Ventilation In Railway Double Track Tunnels On Diesel Traction Lines

A study on the limits for installing mechanical ventilation in railway double track tunnels in operation has been conducted. Both numerical methods and field tests were used in the study. First, present situation of railway double track tunnels; diesel locomotives with its pollutant emissions, and tunnel environmental hygienic standard (TB1912-87) were reviewed. Then a one-dimensional unsteady incompressible flow with moving pollutant source model was proposed. The continuity equation, momentum equation and convection-diffusion equation were discredited using finite volume scheme. Thus a software for predicting the air velocity and pollutant in railway double track tunnels was developed. Afterwards systematic field tests were carried out to evaluate the computation results. Comparison between the computations and field tests shows that the software can provide reliable predictions for natural ventilation cases and that the values for empirical constants including train friction coefficient used by the model are in the proper range. Finally, based on the survey on the ventilation of double (rack tunnels in operation representative parameters were selected and a series of computations were carried o'ut to examine the train passing capacity of tunnels with different lengths and slopes. The result shows that the train passing capacity is closely linked with the train meeting place relative to the tunnel and that the train passing capacity decreases as the tunnel lengths and slops increase. By analyzing the relation between the train passing capacity and tunnel length as well as tunnel slopes the upper and lower limits for installing mechanical ventilation in railway double track tunnel have been determined, which provides science foundations for the formulation the ventilation design norm for railway double track tunnels in operation.