This content is not included in your SAE MOBILUS subscription, or you are not logged in.
To What Degree Do Changes in Gasoline Properties Affect Emissions From European Cars?
Published November 15, 1994 by Societe des Ingenieurs de l'Automobile in France
In response to world-wide interest in the effect of gasoline quality on vehicle emissions, the Shell Companies carried out an international research program to study the effect of compositional variables of gasolines on emissions from European vehicles, whether or not they were equipped with a catalytic converter. The information revealed in this program was proposed as data for the tripartite study of the European Commission that gave rise to the EPEFE program. The chief information revealed by this study is as follows:
Change in the quality of the gasoline can reduce average emissions for a fleet of vehicles, but changing a single characteristic cannot in any way reduce all emissions for all vehicles. There is great variation in vehicle response to changes in fuel properties, primarily with regard to NOx emissions, and the reason for this phenomenon is still not completely understood. A significant portion of the effects observed, especially for NOx, appears to be the result of slight variations in AFR appearing under transitory operation, and due to variations in the stoichiometry of the gasolines.
CO emissions of existing vehicles can be reduced by using peroxides, but these effects are reduced for vehicles employing the latest technology. HC emissions appear to be lower for fuels with a low aromatic content, but this is completely or partially associated with changes in the distillation curve, modifications which result from the compositional change. Reducing the aromatics leads to a reduction in NOx emissions before the catalytic converter, but generally leads to an increase in NOx emissions after the catalytic converter. This is due to the lower efficiency of catalytic converters with gasolines with a low aromatic content.
A scientific understanding of the mechanism involved in these phenomena is of primary importance for future optimization of the engine/gasoline combination.