Tailpipe Emissions and Fuel Economy for 2WD Vehicles and AWD Vehicles Tested on a Double-Axle Chassis Dynamometer: A Comparative Study

Tailpipe emissions, fuel consumption, and wheel torque data were measured for three pairs of vehicles tested over four drive cycles at the Emissions Research and Measurement Section of Environment and Climate Change Canada in Ottawa, Ontario. Each pair of vehicles included identical vehicle models; one vehicle was equipped with an AWD drivetrain and one vehicle was equipped with a FWD drivetrain. The AWD vehicle was tested on a double-axle chassis dynamometer. The amount of AWD activity was heavily dependent on driving behavior and AWD system design. During periods of torque delivery, the percentage of AWD activity ranged between 32% and 57% for the FTP-75 drive cycle, between 3% and 8% for the HWFCT drive cycle, and between 21% and 29% for the US06 drive cycle. The fourth drive cycle was the FTP-75 driven at -7°C. AWD distributions did not show sensitivity to temperature for the first and second vehicle models. The third vehicle model showed increases in AWD activity ranging from 27% to 33% at cold temperature. Vehicle fuel consumption increased with the amount of AWD activity, but was more sensitive to the additional weight of AWD components. Fuel consumption increases ranged between 2.2% and 13.9% for the FTP-75 drive cycle, between 1.6% and 7.8% for the HWFCT drive cycle, between 0.4% and 7.7% for the US06 drive cycle, and between 9.0% and 15.7% for the cold temperature FTP-75 drive cycle. There were no statistically significant differences in emissions of CO, NO_x, and THC between the FWD and AWD vehicles.