Comparison of NOx and PN emissions between Euro 6 petrol and diesel passenger cars under real-world driving conditions

Abstract

With emission standards becoming stricter, nitrogen oxides (NOx) 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 NOx 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 NOx reduction would be much affected. NOx 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. NOx 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. NOx 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.