Improving the Measurement of Chassis Dynamometer Fuel Economy

Obtaining vehicle fuel economy data in conjunction with chassis dynamometer emissions testing is a useful, convenient technique. Data derived in this manner, using EPA city and highway driving cycles, are in wide use. Fuel economy results obtained by carbon mass balance calculation of carbon containing compounds in the vehicle exhaust are at least as accurate and repeatable as those obtained by direct measurement of fuel consumed. Nevertheless, the overall chassis dynamometer-carbon balance fuel economy test yields undesirable variation of results and needs refinement. Major factors influencing the accuracy and repeatability of test results are: CO₂ measurement accuracy; variations in following the driving cycle; vehicle-dynamometer interface conditions; and associated calibration, calculation, test technique and procedural methods and controls employed. Each of these factors is discussed in terms of its relative importance and causal factors, along with suggested or potential means for improvement.