Impact Of Driving Style And Cold Start On Emissions Of Light-duty Vehicles Measured By A Portable Emission Measurement System (PEMS)

Different from the laboratory cycle test method,the real driving emission?RDE?test can not be repeated,and it depends largely on the vehicle dynamics,road conditions and other boundary conditions.Although the RDE regulations have made clear regulations for testing equipment,driving route and data processing methods,the calibration method for dynamic state is not perfect enough.And some neglected boundary conditions in the regulation still have an important impact on the emission results.Therefore,taking light duty gasoline vehicle as the research object,this paper focuses on the impact of driving style and the cold-start on vehicle actual road emission characteristics.Specific tasks are as follows:The RDE test results of different driving styles were compared.Compared to normal driving,the results showed that severe driving caused an elevation of 10-20%for CO₂and 124-833%for CO and 112-234%for PN emission factors,depending on the driver and the vehicle.But the NO_X emission factors had no obvious regularity with the change of driving intensity.Therefore,CO₂ moving average window?MAW?method could not exclude the severe driving point very well.Various dynamic parameters were calculated in order to quantify the driving styles,and the relationship between this parameters and vehicle on-road emissions was also analyzed.For the v·a_pos,the emission factors of CO₂,CO and PN increased with the increase of v·a_pos.When the v·a_pos value was smaller,the more intense the driving styles,the higher the NO_X emission factors.Meanwhile,with the gradual increase of v·a_posos values,the NO_X emissions gradually tended to the same level under different driving styles.For the RPA,the emission factors of CO₂,CO,PN and NO_X increased with the increase of RPA.When RPA>0.7m/s²,CO emissions showed obvious exponential growth relationship,and PN emissions showed a significant linear growth relationship with the change of RPA.The correlation coefficients of RPA,v·a_pos95 and various pollutants were evaluated,and a method for judging the severe driving point was proposed.The results showed that the correlation between PN emissions and RPA,v·a_pos95 was the strongest,followed by CO emissions,the correlation between NO_X emissions and driving parameters was the worst.The correlation coefficient of v·a_pos95 and various pollutant emissions was greater than RPA,and v·a_pos95 evaluation of driving styles was superior to RPA.At the same time,the WLTC v·a_pos upper limit removed the severe driving point,which could significantly reduce the difference between the emission results of different driving behaviors.The MAW method was used to compare pollutant emission factors including cold start data and eliminating cold start data.It was found that CO₂,CO and PN emission factors for the post cold start phase were smaller than for the cold start phase,while the NO_X emissions did not show a similar regular pattern.Therefore,the MAW method was necessary to consider the cold start data into the calculation.The emissions of cold and hot start of vehicle were analyzed within the certain ambient temperature range.The results showed that the shorter the engine extinction time was,the lower the CO and PN emission rates during the start-up phase.NO_X showed completely different results clearly suggesting that the driving style had a more pronounced impact on the emission than the cold and hot state of the vehicle.In particular,vehicles frequently accelerate and decelerate at low speeds.Therefore,in the starting stage of the vehicle,the cold and hot state of the vehicle was one of the main causes of the increase of CO and PN emissions,and driving style was one of the main reasons leading to the increase of NO_X emissions.The influence of vehicle cold start on emission characteristics under different ambient temperatures was evaluated.It was found that,for the cold start phase,the CO₂emission factor was relatively stable.And the CO and NO_X emission factors were the lowest point at about 23?,which showed a clear saddle shape and reflected the influence of the demarcation control strategy.And the PN emission factor was increasing with decreasing temperatures.