Investigation of CO and CO2 distributions from vehicle exhaust in highway tunnels

In this study, the distribution of CO and CO2, which are pollutant gases emitted from the exhausts of vehicles in highway tunnels, in the tunnel was investigated. Firstly, an experimental study limited to CO2 measurements was carried out in Akyazı Tunnel. Then, three-dimensional unsteady flow fields in 500 m long two-lane tunnels with and without vehicles were solved with the Standard k-ε turbulence model. In the first stage of the numerical studies, CO and CO2 distributions inside the tunnel were obtained for different vehicle speeds in straight tunnels with vehicles and curved tunnels with radius of R=950 m and R=1900 m for a vehicle speed of 70 km/h. In the second stage of the numerical studies, the effects of fan thrust, tunnel curvature, number of fans and diffuser blade angle on CO and CO2 levels in the tunnel were investigated in the case of a fan placed 100 m from the tunnel entrance. In the straight tunnel with vehicles, CO and CO2 values decrease as the vehicle speed increases, and in the curved tunnels with vehicles, CO and CO2 values decrease with the effect of curvature. CO and CO2 values decrease as the fan thrust force and number of fans increase in the straight tunnel with fan without vehicles. In the straight tunnel with a single fan at a thrust force of 2035 N and with three identical fans at a thrust force of 950 N, CO and CO2 levels in the tunnel volume decrease at approximately the same rates. The Standard k-ε model used in numerical study shows a good agreement with the experimental data.