Emission Characteristics Of Heavy-duty Diesel Vehicles Under Real-world Driving Conditions

The rapid growth of the vehicle population has brought great challenges to theimprovement of air quality in Chinese cities. As a major contributor of vehicle NOXandPM2.5emissions, heavy-duty diesel vehicle (HDDV) emissions have received muchattention. Further research on real-world HDDV emission characteristics based onon-road testing is needed to develop effective emission control strategies and improveurban air quality.This study is based on second-by-second vehicle velocity and emission data for135HDDVs collected by portable emission measurement systems (PEMS). Usingvehicle specific power (VSP) and instaneous speed (v) as surrogate variables of drivingconditions, an operating binning methodology has been developed in reference to theMOVES model. A database of emission rates and emission factors for HDDVsclassified by vehicle type and emission standard has been established. Results show thatvehicle emission standards have successfully reduced HC, CO and PM2.5emissions forboth buses and trucks. HC, CO and PM2.5emission factors for Euro IV buses are76%,62%and83%lower, respectively, than those for Euro II buses, while HC, CO andPM2.5emission factors for Euro III trucks (including light-duty, medium-duty andheavy-duty trucks) are79-83%,38-51%and36-73%lower than those for Euro I trucks.However, as emission standards became more stringent, the reduction of NOXemissionsis unsatisfactory. No significant difference has been found between Euro IV and Euro IIbuses,while the NOXemission factor for Euro III heavy-duty trucks is similar to that forEuro I heavy-duty trucks, and Euro III medium-duty truck NOXemission factor is39%higher than Euro II truck.By introducing relative emission factors, the influence of driving conditions onHDDV emissions has been studied using a micro-trip method. The correlations betweenrelative HC, CO and NOXemission factors and average speed for both buses and trucksfit the power function best, and the coefficients of determination are between0.5to0.9.However, no obvious correlations between the relative PM2.5emission factor andaverage speed for either buses or trucks have been found; the coefficients ofdetermination for the PM2.5speed correction curves are less than0.3.For comparison with emission limits, brake-specific emission factors for both buses and trucks have also been developed. Results show that bus and truck emissionsunder actual on-road driving condition are higher than those developed for typeapproval. On-road brake-specific emission factors of CO, NOXand PM2.5for buses are1.7-7.1times the emission limits, while on-road brake-specific emission factors of NOXand PM2.5for trucks are1.3-6.3times the emission limits.HDDV emission inventories for five typical cities in the Yangtze River Delta havebeen established based on the results above. During2000-2010, HDDV emissions ofHC, CO and PM2.5in all these cities have began to decline, while NOXemissionscontinue to increase. HDDVs are major sources of vehicle NOXand PM2.5emissionsand account for58-77%and83-90%of total NOXand PM2.5emissions from vehiclesduring last10years. In order to achieve the NOXemission reduction target set up by theTwelfth Five Year Plan, the implementation of Euro IV HDDV emission standards isessential, while other control measures such as scrapping of older trucks and thepromotion of low emission buses are also needed.