Variations of significant contribution regions of NOx and PN emissions for passenger cars in the real-world driving

Abstract

Nitrogen oxides (NOx) and particulate number (PN) emissions are the main concerns of the passenger cars in the real-world driving. NOx and PN emissions are greatly dependent on the driving behaviors which differ significantly between standard driving cycles and real-world driving. However, the significant contribution regions (short durations corresponding to high proportions of total emissions) of NOx and PN emissions regarding different driving behaviors (e.g. vehicle speed and acceleration) are still uncovered. NOx20% and NOx50% refer to instantaneous NOx emission rates when NOx emission rates are ranked from high to low level where the sums of NOx emission rates being higher than NOx20% and NOx50% correspond to 20% and 50% of total NOx emissions, respectively. t20% and t50% are corresponding durations where NOx emission rates are higher than NOx20% and NOx50%. In this paper, three Euro-6 compliant direct injection gasoline passenger cars and a diesel passenger car are tested in a real-world driving trial in which nineteen drivers are involved. Novel key performance indicators with reference to the regimes of specific NOx and PN contributions to total emissions are defined. Instantaneous NOx and PN emissions are monitored using a portable emission measurement system (PEMS) in the test. The results indicate that the maximum and minimum average speed over the four cars being approximately 32.3 km/h s and 42.6 km/h, respectively. Average PN emission factor of the diesel car is the lowest among the four given cars. Average t20% and t50% corresponding to NOx20% and NOx50% are lower than 3% and 12%, respectively, for all the passenger cars; additionally, these two parameters show the same pattern. The corresponding t20% and t50% variations of the Euro-6a gasoline car and the diesel car are much lower than the other two. Average acceleration corresponding to 20% and 50% of total NOx emissions for the given diesel car is approximately 1.25 m/s2 and 0.6 m/s2, respectively, being much higher than that of the other three gasoline cars (lower than 1 m/s2 and 0.4 m/s2 respectively) over the specific driving route and drivers. The average PN20% and PN50% of the given diesel car are approximately 7 × 107#/s and 3 × 107#/s respectively, being much lower than the three given gasoline cars (higher than 8 ×109#/s and 2 ×109#/s respectively) under the given test conditions; the corresponding t20% and t50% are lower than 4% and 17% respectively for all the three gasoline cars.