Study On Emission Characteristics Of Light-duty Vehicles In Real Driving Conditions

The number of vehicles in China increases rapidly with the growing economics,which leads to environmental issues concerned by the mass.Although standard laboratory test cycles are specified in the emission regulation throughout the world,it has been proved by massive studies that it is unable to contain all the operating conditions that are possible under real-driving condition in these laboratory cycles,and thus the real-driving emission may differ greatly with the laboratory test emission.Under these circumstances,real driving emission（RDE）test has been added in the amendment of Euro 6 regulation to control the in-use emission from vehicles.This thesis tested the emissions from 10 vehicles with different kinds of fuel and certified to different emission standards using portable emission measurement system（PEMS）in accordance with the RDE regulation under real driving condition in Beijing.These vehicles include 3 diesel vehicles,6 gasoline vehicles and one hybrid vehicle.Over60 thousand pieces of data have been recorded and they are processed by the CO₂ moving average method and the power level grouping method.The results show that:for diesel vehicles,the CO emissions from the tested vehicles are in compliance with the emission regulation in terms of both standard test cycles and RDE cycle,while the conformity factors（CF）of NOx are greater than those of CO,and significantly greater than the regulation limit,with a maximum of 7.09 times the limit;for gasoline vehicles,both the CO emissions and the NOx emissions are lower than the limit,and the CF of CO are greater than those of NOx under real driving condition using the CO₂moving average method,and the CFs from three of all the gasoline vehicles are greater than the limit,with a maximum CF of 3.61;the emissions of NOx from diesel vehicles and CO from gasoline vehicles under real driving condition differ the most with those under standard cycles,and the instantaneous NOx emission from diesel vehicles and the instantaneous CO emissions from gasoline vehicles increase sharply with the increase of acceleration under the rural and the highway conditions,and the highest instantaneous emissions occur under high speed&high load condition.The results of PN emissions show that:the PN emissions deviate a lot under the rural and the highway conditions while a little under the urban condition;the PN emission factors of diesel vehicles with DPF are lower than those of gasoline vehicles.The accumulating direction of CO₂ window may influence the number of windows but can seldom change the emission results.The validation of the RDE results from 6 vehicles shows that most failure cases are caused by excessive dynamic characteristics;the influence of validation on emission results is to be further studied.