Front-End Volatility Requirements of Late Model Cars at Intermediate Ambient Temperatures

The response of 1975-1981 model year vehicles to front-end fuel volatility was measured in a consumer survey carried out in Houston in the winter of 1981-82. Two hundred ten customers, approximating the car population for these years, were given gasolines varying in front-end volatility. Responses to these changes in volatility were measured by weekly telephone interviews with each customer. Results show that existing ASTM volatility specifications (Volatility Class E ASTM D 439) provides hot engine driveability protection at 68 °F (20.0°C) and even greater protection below 68 °F. Sluggish performance (smooth acceleration but at a reduced rate) was the major hot driveability problem observed with fuels of high volatility, with occasional stalling, rough idle and poor hot start being significant but lesser problems. No vehicles suffered disabling vapor lock even on the most volatile fuel tested. Thus, the ASTM volatility specifications provide a significant measure of overprotection against the serious customer inconvenience and safety concerns associated with road stoppage. Incorporation of narrower temperature ranges and more volatility classes in the specifications would maintain the demonstrated high level of protection with no loss in performance and would allow gasoline refiners greater flexibility in utilizing high octane light ends.