On road Fuel Economy and Emission measurements
Scott Sluder


Abstract: The purpose of this study is to develop for determining the on-road emissions and fuel consumption of modern vehicles. The strategy used to accomplish this task was to define the vehicle’s on-road operating envelope, followed by dynamometer measurement of emissions at specific operating points.

The speed of a vehicle over level road is a function of the engine speed and gear ratio. Similarly, the acceleration of a vehicle is a function of engine speed, engine load and gear ratio. Tail pipe emissions are both functions of the engine speed and engine load. Therefore, the emissions and the fuel consumption of a vehicle can be related to the vehicle’s speed and acceleration, since these two quantities are in turn related to the engine speed and engine load for a given gear ratio.

The operating point of an engine can be defined by noting the values of several operational parameters. Most often these parameters consist simply of the engine speed and a variable indicative of engine load, such as manifold absolute operating pressure. Other variables, which are important in defining operating point, are coolant temperature, air consumption, fuel consumption, and throttle position.

Characterization of the vehicle’s operating envelope requires extensive testing of the vehicle on-road. If the vehicle has a manual transmission, several fixed throttle position acceleration must be completed in each gear. Similarly, several fixed throttle deceleration tests must be completed. Lastly, steady speed tests at several speeds for each gear must be completed. The result of this testing is an envelope of accelerations which are possible at each vehicle speed. The vehicle actual acceleration at any speed, and hence the fuel consumption and tailpipe emissions, is then dependent upon the throttle position and gear ratio. Hence, by completely defining the vehicle as described followed by measurement of the tailpipe emissions and fuel consumption during identical tests performed on a chassis dynamometer, a database can be assembled which relates speed and acceleration to tailpipe emissions and fuel consumption.

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Point of Contact: David Irick (phone: 865-974-0863, dki@utk.edu)