Evaluating the Performance of Driveability Indices: A Correlation with the Enthalpy of Vapour Formation for Gasoline

It is desirable to predict the cold weather driveability performance of fuels by means of an index based on simple measurements such as the ASTM distillation curve. In the past, several such indices have been proposed from the analysis of vehicle test results. In contrast, this paper describes how a driveability index can be derived from first principles - namely, the physics of fuel vapour formation.

A number of present and proposed driveability indices were evaluated by comparing the way they correlate with the calculated enthalpy requirement of fuels. It is concluded that E100+E150 best meets the need for a simple index and is robust across a range of air/fuel ratios.