Assessing and Characterizing the Effect of Altitude on Fuel Economy, Particle Number and Gaseous Emissions Performance of Gasoline Vehicles under Real Driving

High altitudes have a significant effect on the real driving emissions (RDE) of vehicles due to lower pressure and insufficient oxygen concentration. In addition, type approval tests for light-duty vehicles are usually conducted at altitudes below 1000 m. In order to investigate the influence of high altitude on vehicles fuel economy and emissions, RDE tests procedure had been introduced in the China VI emission regulations. In this study, the effect of altitude on fuel economy and real road emissions of three light-duty gasoline vehicles was investigated. The results indicated that for vehicles fuel economy, fuel consumption (L/100 km) for the tested vehicles decreased while the mean exhaust temperature increased with an increase in altitudes. Compared to near sea level, the fuel consumption (L/100 km) of the tested vehicle was reduced by up to 23.28%. For emissions, carbon monoxide (CO) and particle number (PN) emissions consistently increased and nitrogen oxide (NO_X) emissions first increased and then decreased with an increase in altitude. At specific test modes, the CO emissions of tested vehicles were urban > rural > motorway in descending order. Compared to near sea level, NO_X emissions increased slightly at an altitude of 2300 m, while PN emissions increased by up to 20 times or more. Therefore, the reasonableness of altitude expansion factor development needed to be considered when refining RDE regulations. For vehicle manufacturers, the focus should be on PN emissions at high altitude regions.