Comparison of Real-World Urban Driving Route PEMS Fuel Economy with Chassis Dynamometer CVS Results

The use of portable emissions measurement systems (PEMS) for testing vehicle emissions while driving on the road has been demonstrated as early as the 1980s. Many users have taken the driving route and repeated the route in a chassis cell with the same vehicle expecting identical results. Emission results can be comparable but there are many factors that need to be considered. This study compares PEMS results for a driving route repeated across seasons and traffic conditions with a single vehicle. The ambient temperature variability and traffic is shown to cause variation in emissions for any individual run. Generating a test cycle to mimic the driving route can be done in a variety of ways. The simplest is to take an individual driving run and translate the time and speed trace directly. This does not address the statistical results from numerous driving runs on the same route. A variety of test cycles are performed in the chassis cell with the same vehicle used to drive the route with results shown. Additionally, the chassis dynamometer used for the laboratory confirmation has the capability for grade adjustment. This study demonstrates the impact of using grade in addition to the time and speed trace for correlation work. The GPS signal is used to generate altitude values for this study. When GPS data is used to generate grade, significant GPS altitude reading error is included in the testing. An evaluation of this error and different averaging techniques used are evaluated for use with the grade simulation in the test cell.