Comparison of fine particles emissions of light-duty gasoline vehicles from chassis dynamometer tests and on-road measurements

Abstract

Fine particles are highly related to human health, especially ultrafine particles and nanoparticles. The mass of emissions from a gasoline vehicle is relatively lower than that of a diesel vehicle, but the number of gasoline vehicles in China is so huge that the number of fine particles can't be ignored. An on-board measurement system was established to measure the instantaneous number and mass size distributions of fine particles emitted from a light-duty gasoline vehicle under a real-world driving condition. The exhaust gas was sampled from the inside of the tailpipe. Measurements were carried out using a light-duty gasoline vehicle for goods on a chassis dynamometer and on urban streets in a downtown area of Nanjing. Size and time resolved data were obtained from an Engine Exhaust Particle Sizer (EEPS). The system was operated under the New European Driving Cycle (NEDC) and steady-state speed tests. The comparisons of size distribution and number concentration (NC) in different driving cycles in the real-world with the results from the chassis dynamometer are shown. The time proportion of operating modes in NEDC is different from that on real urban roads. The particle sizes for the NCs obey a bimodal distribution from the on-road data with mode sizes of 10.8 nm and 39.2 nm, while those from the chassis dynamometer tests obey a unimodal distribution with a mode size of 10.8 nm. The maximum NCs of particles were increased as the vehicle operating modes changed from idling, cursing to deceleration and acceleration from the on-board measurements, while compared to that from the on-board measurements, the maximum concentrations at the mode size were however in different order and the cruising mode became the second highest peak instead of the deceleration mode. The ratios of the NCs from the chassis dynamometers to that from on-road data in the speed of 15 km h−1, 32 km h−1, and 50 km h−1 are 2.78, 2.19, and 0.48, respectively. Similarly for the mass concentration the ratios are 0.19, 0.17, and 0.009, respectively. The acceleration in the interval of 0.6–0.9 m s−2 has the greatest influence on the NC in on-road measurements, while the acceleration of 0.52 m s−2 has the most significant impact on the NC in the chassis dynamometer tests. The vehicle load increases the total number and mass concentration in a small range, showing no significant impact on particles size distribution especially the nanoparticles. The comparison shows that the fine particle emissions are indeed different between the NEDC and the on-road measurements in Nanjing. The differences show that the fine particles emission on the real road can't be represented well by the results in the NEDC, and the corresponding errors should be in consideration when the vehicle emissions from the NEDC are applied. The study makes us clear that the fine particles emission characteristics of the light-duty vehicle on the urban roads are really different with that in the NEDC.