Gasoline Driveability Index, Ethanol Content and Cold-Start/Warm-Up Vehicle Performance

During 2003 the Coordinating Research Council conducted an intermediate ambient temperature vehicle driveability research program. The objective of the program was to determine the effects of ethanol content on cold-start and warm-up driveability. Twenty-seven latest technology fuel injected vehicles, which included passenger cars, vans, and light duty trucks, were used to evaluate ten test fuels. A hydrocarbon-only base fuel was blended to have a nominal 1300 Driveability Index (DI). Three ethanol containing fuels were produced by splash blending 3, 6, and 10 volume percent ethanol into the base fuel. Three additional ethanol fuels containing 3, 6, and 10 volume percent ethanol were produced to nominally match the 1300 DI volatility characteristics of the hydrocarbon-only base fuel. Three hydrocarbon-only fuels were produced using the base fuel and light hydrocarbons to nominally match the volatility characteristics of the 3, 6, and 10 volume percent ethanol splash blended fuels. Cold-start and warm-up driveability tests were conducted in the ambient temperature range of -1°C - 4°C (30°F - 40°F). As DI increased over the range 1250 - 1300, cold-start and warm-up driveability became poorer. The program revealed that DI alone was not a good predictor of performance for both hydrocarbon-only and ethanol blended fuels. Driveability performance models were developed for a combination of hydrocarbon-only and ethanol blended gasolines. These findings will be useful in possible future investigations to define the impact of ethanol on Driveability Index of fuels with Driveability Indices less than 1250 as specified in ASTM D 4814, Standard Specification for Automotive Spark-Ignition Engine Fuel. Two models were developed based on DI, one including an ethanol content term and the other model with an ethanol term independent of concentration. Surprisingly, both equations provided similar predictive precision.