Large eddy simulation of vehicle emissions dispersion: Implications for on-road remote sensing measurements

Yuhan Huang; Elvin C Y Ng; Nic C Surawski; Yat-Shing Yam; Wai-Chuen Mok; Chun-Ho Liu; John L Zhou; Bruce Organ; Edward F C Chan

doi:10.1016/j.envpol.2020.113974

Large eddy simulation of vehicle emissions dispersion: Implications for on-road remote sensing measurements

Environ Pollut. 2020 Apr:259:113974. doi: 10.1016/j.envpol.2020.113974. Epub 2020 Jan 11.

Authors

Yuhan Huang¹, Elvin C Y Ng², Nic C Surawski³, Yat-Shing Yam⁴, Wai-Chuen Mok⁵, Chun-Ho Liu⁶, John L Zhou⁷, Bruce Organ⁸, Edward F C Chan⁹

Affiliations

¹ Centre for Green Technology, School of Civil and Environmental Engineering, University of Technology Sydney, NSW, 2007, Australia. Electronic address: yuhan.huang@uts.edu.au.
² Centre for Green Technology, School of Civil and Environmental Engineering, University of Technology Sydney, NSW, 2007, Australia; Jockey Club Heavy Vehicle Emissions Testing and Research Centre, Vocational Training Council, Hong Kong, China. Electronic address: elvin_ng@vtc.edu.hk.
³ Centre for Green Technology, School of Civil and Environmental Engineering, University of Technology Sydney, NSW, 2007, Australia. Electronic address: Nicholas.Surawski@uts.edu.au.
⁴ Environmental Protection Department, Hong Kong Special Administrative Region Government, Hong Kong, China. Electronic address: y_s_yam@epd.gov.hk.
⁵ Centre for Green Technology, School of Civil and Environmental Engineering, University of Technology Sydney, NSW, 2007, Australia; Department of Mechanical Engineering, The University of Hong Kong, Hong Kong, China. Electronic address: wcmok888@hotmail.com.
⁶ Department of Mechanical Engineering, The University of Hong Kong, Hong Kong, China. Electronic address: chliu@hku.hk.
⁷ Centre for Green Technology, School of Civil and Environmental Engineering, University of Technology Sydney, NSW, 2007, Australia. Electronic address: junliang.zhou@uts.edu.au.
⁸ Centre for Green Technology, School of Civil and Environmental Engineering, University of Technology Sydney, NSW, 2007, Australia; Jockey Club Heavy Vehicle Emissions Testing and Research Centre, Vocational Training Council, Hong Kong, China. Electronic address: bruceorgan@vtc.edu.hk.
⁹ Centre for Green Technology, School of Civil and Environmental Engineering, University of Technology Sydney, NSW, 2007, Australia; Faculty of Science and Technology, Technological and Higher Education Institute of Hong Kong, Hong Kong, China. Electronic address: eddychan@vtc.edu.hk.

PMID: 32023804
DOI: 10.1016/j.envpol.2020.113974

Abstract

On-road remote sensing technology measures the concentration ratios of pollutants over CO₂ in the exhaust plume in half a second when a vehicle passes by a measurement site, providing a rapid, non-intrusive and economic tool for vehicle emissions monitoring and control. A key assumption in such measurement is that the emission ratios are constant for a given plume. However, there is a lack of study on this assumption, whose validity could be affected by a number of factors, especially the engine operating conditions and turbulence. To guide the development of the next-generation remote sensing system, this study is conducted to investigate the effects of various factors on the emissions dispersion process in the vehicle near-wake region and their effects on remote sensing measurement. The emissions dispersion process is modelled using Large Eddy Simulation (LES). The studied factors include the height of the remote sensing beam, vehicle speed, acceleration and side wind. The results show that the measurable CO₂ and NO exhaust plumes are relatively short at 30 km/h cruising speed, indicating that a large percentage of remote sensing readings within the measurement duration (0.5 s) are below the sensor detection limit which would distort the derived emission ratio. In addition, the valid measurement region of NO/CO₂ emission ratio is even shorter than the measurable plume and is at the tailpipe height. The effect of vehicle speed (30-90 km/h) on the measurable plume length is insignificant. Under deceleration condition, the length of the valid NO/CO₂ measurement region is shorter than under cruising and acceleration conditions. Side winds from the far-tailpipe direction have a significant effect on remote sensing measurements. The implications of these findings are discussed and possible solutions to improve the accuracy of remote sensing measurement are proposed.

Keywords: Computational fluid dynamics; Exhaust plume dispersion; Near-wake region; On-road emission test.

MeSH terms

Air Pollutants*
Environmental Monitoring*
Motor Vehicles
Remote Sensing Technology
Vehicle Emissions*

Substances

Air Pollutants
Vehicle Emissions