Freight train air brake modelling with emergency valves

The 120-type air brake system is unique around global rail industry and critical for Chinese freight train operation. Existing research about its simulations does not include detailed models for the emergency brake valves. This paper filled this research gap by developing a detailed fluid dynamic air brake system with a focus on the emergency brake valve. The working principle of the emergency brake vale was reviewed. The brake system model was based on gas flow governing equations (mass and momentum) and orifice flow equations. The model was validated by comparing with measured data from a 150-wagon train. Four braking scenarios were compared. The simulated maximum cylinder pressure was only 5 kPa out of the range of the measured data. The maximum difference regarding the time when cylinder pressure reaches maximum pressure was 4 s. The simulation results have also shown variable switch pressure points for the two-stage brake valve. This is agreed by the measured results and was not shown in previously published research.