Accuracy of exhaust emissions measurements on vehicle bench

Ten European laboratories worked together to study the influence of a lot of parameters of the measurement of light vehicle emission factors on vehicle bench, in order to improve the accuracy, reliability and representativeness of emission factors: driving patterns (driving cycles, gear choice behaviour, driver and cycle following), vehicle related parameters (technical characteristics of the vehicle, emission stability, emission degradation, fuel properties, vehicle cooling and preconditioning), vehicle sampling (method, sample size), and laboratory related parameters (ambient temperature and humidity, dynamometer setting, dilution ratio, heated line sampling temperature, PM filter preconditioning, response time, dilution air). The results are based on literature synthesis, on about 2700 specific tests with 183 vehicles and on the reprocessing of more than 900 tests. These tests concern the regulated atmospheric pollutants and pre-Euro to Euro 4 vehicles. We did not find any influence of 7 parameters, and find only a qualitative influence for 7 other parameters. 6 parameters have a clear and quantifiable influence and 5 among them allow us to design correction factors to normalise emission measurements: gearshift strategy, vehicle mileage, ambient temperature and humidity, dilution ratio. The sixth influencing parameter is the driving cycle, sometimes more significant than the fuel or the emission standard. The results allow us to design recommendations or guidelines for the emission factor measurement method.