Effect of Volatility Changes on Vehicle Cold-Start Driveability

Controlled cold-start driveabilily tests using an urban driving cycle were conducted on fifty-one customer vehicles representing 1972-1988 models typically on the road in New England. Tests were conducted at ambient temperatures of 21-30°F with two test fuels and the fuel found in the vehicle tank. Nineteen vehicles (37% of the total fleet) showed significant deterioration in driveability performance with a low Reid Vapor Pressure (BVP) test fuel (nominal 9.0 psi) compared to a typical RVP fuel (nominal 13.5 psi). These nineteen cars showed, on average, four times as many driving stalls and almost three times as many heavy hesitations with the low RVP fuel. Consumer-type driveability tests conducted with 1984-1988 model cars confirm that reducing volatility to the levels adopted by some northeastern U.S. states and being considered by EPA (9.0 psi maximum in areas permitted up to 11.5 psi by ASTM D 439 (1)*) can result in decreased customer satisfaction, particularly in the transition before and after the mandated low RVP period when ambient temperatures are lower and the low RVP summer gasoline is being phased into or out of the distribution system.