Vehicle Drive Cycle Fuel Economy Prediction Using Single Cylinder Engine Data

The confluence of fuel economy improvement requirements and increased use of ethanol as a gasoline blend component has led to various studies into the efficiency and performance benefits to be had when using high octane number, high ethanol content fuels in modern engines. As part of a comprehensive study of the autoignition of fuels in both the CFR octane rating engine and a modern, direct injection, turbocharged spark ignited engine, a series of fuel blends were prepared with market relevant ranges of octane numbers and ethanol blends levels. The paper reports on the first part of this study where fuel flow measurements were done on a single cylinder research engine, utilizing a GM LHU combustion system, and then used to predict drive cycle fuel economy. For a range of engine speeds and manifold air pressures, spark timing was adjusted to achieve either the maximum brake torque (MBT) or a matched 50 % mass fraction burnt location. At operating conditions where combustion was knock limited, the spark was retarded to achieve a consistent knock intensity based on peak-to-peak pressure values as determined by in-cylinder pressure measurements. These fuel flow maps were introduced into a vehicle model to predict drive cycle fuel economy of a passenger car utilizing the same engine configuration. The precited fuel economy numbers over FTP-75, Highway and US06 drive cycles were compared with certification values - using a certification fuel - and yielded a reasonable comparison without the need for model parameter adjustments. Next, the fuel economy values of the various test fuels were predicted in a similar manner and the comparison of the results revealed not only the impact of knock limit differences, but also the impact of energy density at non-knocking operating points.