Gasoline Distillation Effect on Vehicle Cold Start Driveability 2007-01-4073

Cold start vehicle driveability performance depends on many parameters, one of which is the distillation character of the fuel. In the late 90's, a gasoline driveability index (DI) was developed for spark ignited combustion vehicles by a consortium of automotive and petroleum industry scientists based on correlation studies between controlled fuel quality matrices and vehicle performance under specific ambient conditions. The DI equation uses a weighted sum of gasoline distillation temperatures at the 10, 50 and 90 percent evaporation volumes, commonly called T₁₀, T₅₀ and T₉₀. These three distillation volatility points are specified by the ASTM International D 4814 fuel specification and are seasonally adjusted. This paper studies the cold start driveability performance of Federal EPA Bin 5 and Bin 8 vehicles with respect to fuel distillation characteristics at temperatures other than T₁₀, T₅₀ and T₉₀. Fuels studied include regular Summer-grade unleaded gasoline, high-DI (1255°F), high-DI with high-T₇₀, and high-DI with both high T₃₀ and T₇₀. The results demonstrate that, although the latest vehicles can tolerate high-DI fuel in cold start driveability, the performance is deteriorated in some vehicles with the high-T₇₀ and the combined high T₃₀ and T₇₀ test fuels. The degree of poor cold start performance also depends on the ambient conditions. Summer weather with high-dew point temperatures experienced more cold start driveability performance demerits with the two test fuels as compared to normal Summer quality gasoline. Gasoline survey data shows that high T₇₀ fuels are available in the market place, but appear to be regionally isolated. When these high T₇₀ or high in both T₇₀ and T₃₀ gasoline blends show up in the field it has resulted in severe vehicle owner dissatisfaction. The mechanism of the poor cold start performance with such fuels is discussed.