Objective of the investigation: Determine the number and arrangement of jet fans to be installed in the Acapulco Tunnel that will ensure an air quality that meets international standards for vehicle occupants. Cement coating finish Results comparison with specialized design programs axial and transversal distribution of pollutants

Acapulco Roadway Tunnel Lenght: 3 km Time savings during congestion: 1 h to 10 min.

PHOENICS GENERAL EQUATION

For carbon monoxide (CO) concentration: Vehicle emissions represented as a line source of 5.5 ppm/(m 3 s) per lane, corresponds to the design vehicular density of 1,381 pv/h per lane (pv := passenger vehicle) Emission factor of f CO = 1 m 3 /(h.pv) (U.S. emission factor standard for 1989 was 0.6 m 3 /(h.pv) and 2.1 m 3 /(h.pv) in 1967) Preliminary calculations show that 10 air volume changes per hour would allow sufficient dilution of the CO gas so that the maximum concentration would be 150 ppm. This is a flow rate of 716 m 3 /s.

Jet-fan characteristics: 45 kW rating jet-fans have a thrust of 2.86 kN Air density of 1.19 kg a /m 3 Jet area at the exit of m 2 Exit velocity of 34 m/s.

Acapulco Tunnel geometrical characteristics: length of 2,947 m cross sectional area of m 2 hydraulic diameter of 9.66 m.

PERSPECTIVAS Tunnel dimensions in m

Jet fan arrangement for 24 units of 45 kW rating

Grid distribution in the transverse plane

RESULTS Cement finished tunnel walls with a surface roughness of 3 mm, there was an improved performance for 24 jet-fans with 3 fans in the cross section as CO concentrations were lower than 100 ppm in the last 500 m of the tunnel, with a low rate of 760 m 3 /s. Momentum source and sink that is due to the vehicle drag in the three tunnel lanes. An increase in wall-roughness was also considered due to tunnel appurtenances such as signs, cable ducts, for which a friction factor of was implemented that corresponds to an equivalent wall roughness of 2.5 cm. In this case the flow rate obtained with 24 jet-fans, 2 in the cross section, was 469 m 3 /s, a 37% reduction. However, the maximum CO concentration was 148 ppm near ground level at 22 m from the exit portal, which is under the 150 ppm design limit.

RESULTS The momentum sink for the two counterflow lanes was kN, while the momentum source for the concurrent lane was 3.2 kN. If the tunnel is unidirectional (i.e. the three lanes are with concurrent traffic/air flow) then for the same power input there would be a 50 % increase in the flow rate and a 20 % decrease in the maximum CO concentration.

CONCLUSIONS and RECOMMENDATIONS A fairly straightforward model that calculates the required number of jet-fans for an axially ventilated roadway tunnel has been implemented in PHOENICS. The optimum design can be investigated based on the spatially calculated carbon monoxide concentration distribution. The overall effect of vehicle drag for countercurrent traffic lanes is considerable; and although it was herein simplified by «moving plates» the results are conservative thus providing a «safety factor» for the maximum ground level CO concentrations allowed. The calculations derived form an integral approach are based on a very rough estimate of the overall friction factor, and the drag coefficient that is experimentally derived for one vehicle. The overall result would tend to overestimate the required number of jet-fans.

CONCLUSIONS and RECOMMENDATIONS The intermittent nature of vehicle drag effect should be further investigated to have a more realistic mixing effect of the ground level vehicle emissions, and for the fan power requirements for a design airflow rate. The interaction of the wind on the tunnel portals and traffic induced airflows should also be further investigated in order to derive worst-case scenarios. The present model can also be used to investigate a jet-fan operational policy in case of a fire inside the tunnel to ensure maximum safety for trapped vehicle passenger evacuation as well as for fire fighters.