Abstract
.In this study, we continue to analyze the diffusion mechanism of ultrafine particles and the particle coagulation phenomenon with a size range of 26-287 nm exhausted from vehicles during the process of passing through a 100-m-long tunnel using the realizable k-ε model and dynamic grid technique. A three-dimensional model consisting of a 100-m highway tunnel and four side-by-side gasoline vehicles (L × W × H = 4.5 m × 1.8 m × 1.5 m) was established in the STAR-CCM+ computational fluid dynamics software. The gasoline vehicles traveled simultaneously under different situations of three driving speeds of 60 km h-1, 40 km h-1, and 20 km h-1 during the simulation. Through data analysis and research, it was found that the coagulation process of particles is very complicated, especially at low speeds. When the vehicle speed is 20 km h-1, the variation in particle concentration at the vehicle wake near the tailpipe (at the vertical plane located 0.1 m behind the exhaust pipe) causes a large error if the coagulation action is not considered. The relative error of the average particle concentration at 0.5 s of the vertical section 0.1 m away from the exhaust pipe is as high as 193.51%. The relative error in the entire tunnel is only 2.82%, which is less than 5%. Thus, it is recommended that particle coagulation should be considered when analyzing particle dispersion in the near-wake region behind the vehicle and the breathing areas, especially when the vehicle travels slowly inside the tunnel. However, when evaluating the particle concentration and exposure levels for the entire tunnel, coagulation can be ignored without significant errors, especially at a high vehicle speeds. This study clarified the importance of coagulation in different areas and its influence on the diffusion of particulate matter. This is conducive to further analysis of the diffusion characteristics of particulate matter and can appreciably reduce the pollution degree in a tunnel by changing the coagulation efficiency of particulate matter in the future.
Highlights
The number of motor vehicles in China has increased substantially, and ultrafine particles in automobile exhaust have become one of the most important pollution sources in urban areas
(2016) simulated the time scale evolution of particle size distribution during vehicle exhaust emissions and dilution, pointed out that in a closed environment, such as a road tunnel, the diffusion of particulate matter is generated by the limited airflow in the tunnel, which is different from the characteristics of an open environment
When the vehicle moves at a lower speed of 20km h-1, the thermal buoyancy effect caused by the temperature difference between the vehicle exhaust and the atmospheric environment is more significant than when driving at high speed, hot vehicle exhaust plume overall rising trend
Summary
The number of motor vehicles in China has increased substantially, and ultrafine particles in automobile exhaust have become one of the most important pollution sources in urban areas. Studies have shown that the exposure to ultrafine particulate matter affects the incidence of cardiovascular disease and systemic inflammation (Kevin J et al, 2016). The ventilation systems in closed tunnels at cities in China are closed or semi-closed in the majority throughout the year, which leads to the continuous accumulation of fine and ultrafine particles in urban tunnels. (2016) simulated the time scale evolution of particle size distribution during vehicle exhaust emissions and dilution, pointed out that in a closed environment, such as a road tunnel, the diffusion of particulate matter is generated by the limited airflow in the tunnel, which is different from the characteristics of an open environment. In a confined environment as a road tunnel the coagulation and deposition play an important role, as it was concluded by Gidhagen et al (2003), Sturm et al (2003) and Park et al (2004)
Sign-in/Register to view highlights & summary 
Submitted Version (
Free)
Published Version
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call