Insight into the penalty of exhaust emissions and fuel consumption by DPF regeneration of a diesel passenger car.

In order to keep high fuel economy of diesel passenger cars, Diesel particulate filter (DPF) is periodically regenerated. In the regeneration process, extra fuel is injected into combustion chambers to achieve high exhaust temperature for the purpose of oxidizing particles accumulating on DPF substrate. It generates significant impacts on passenger car performance and exhaust emissions. In this paper, real-driving performance and exhaust emissions of a diesel car were tested over sixteen drivers under real-world conditions. DPF regeneration events were identified via exhaust temperature. Vehicle power output, fuel economy, and exhaust emissions in the trips both with and without DPF regeneration were analyzed. The results indicated that DPF regeneration events occurred in three of thirty-two test trips, and the maximum exhaust temperature was 250 °C during DPF regeneration. The DPF regeneration event led to the decrease of fuel economy and the increase of particle number, nitrogen oxides and carbon dioxides emission. Particle number emission factors were increased from approximately 109 #/km to 5 × 1010 #/km during DPF regeneration. The average power output of the car was in the range of 14.5 kW-15.6 kW and 15.8 kW-18.4 kW for the trips with and without DPF regeneration, respectively. However, Carbon monoxide emission factors were insensitive to DPF regeneration in the test trips.

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

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.