Comparison of NO x and PN emissions between Euro 6 petrol and diesel passenger cars under real-world driving conditions

Highlights: • NO_x and PN emissions of Euro 6 passenger cars are tested under real-world conditions. • Comparisons in NO_x and PN emissions for petrol and diesel cars are made. • Significant high NO_x and PN concentrations are observed in petrol passenger cars. • Relationships between NO_x and PN emission factors and driving behaviours are analysed. With emission standards becoming stricter, nitrogen oxides (NO_x) and particle number (PN) emissions are the main concerns of modern passenger cars, especially for the real-world driving. In this paper, two direct injection (DI) petrol passenger cars and a diesel passenger car are tested on the same routes, driven by the same driver. Instantaneous NO_x and PN emissions are monitored by a portable emission measurement system (PEMS) in the tests. During the real-world driving, the exhaust temperatures of the two petrol cars are sufficiently high to ensure high efficiency of three-way catalysts (TWCs). On the other hand, the exhaust temperatures of the diesel car in some sections of the route are lower than the crucial light-off temperature of the selective catalytic reduction (SCR) below which its effectiveness in NO_x reduction would be much affected. NO_x and PN concentrations are low during motorway driving for the petrol passenger car equipped with a gasoline particulate filter (GPF); however, they are high and change frequently in the whole journey for the petrol passenger car without a GPF. NO_x emission factors are quite low over most of the driving sections for the diesel car, but some significant high peaks are observed in the acceleration process. NO_x emission distributions over speed and acceleration are similar for both petrol cars; and they differ significantly from the diesel counterpart. Particle size from the diesel car is the largest, followed by the petrol car with a GPF.