A Review of the Effect of Petrol Composition on Unregulated Motor Vehicle Emissions with Particular Emphasis on Non-Catalyst Vehicles

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Abstract
Over the period covered by this review many changes have been made to fuel composition. A number of these changes have been made with the intention of improving the environment by altering exhaust emissions. On some occasions it appears that refiners may have removed one hazard only to create another. A typical example is the introduction of oxygenates at the expense of aromatics. Our review shows that this will reduce benzene and aromatic emissions but will increase aldehyde emissions. The use of catalytic converters minimises many of these fuel effects but in many countries the catalytic vehicle population is small and these fuel changes may have significant effects if the fuels are used in cars not fitted with exhaust treatment devices. Concern grows regarding vehicular emissions as the number of vehicles continues to rise. It becomes even more important that we understand the environmental effects that changing fuel compositions will have. Particularly indicted appears to be the increase in the use of aromatics in fuel. This leads to an increase in the known carcinogen benzene and polynuclear aromatics as well as contributing to photochemical smog. Yet the approach of reducing aromatics and increasing oxygenates may not necessarily be the best option for vehicles without some form of exhaust treatment system. Additionally raising the alkene content of fuel has been shown to increase 1:3 butadiene emissions but increasing the alkane concentration leads to the formation of photochemically active alkenes. Solving the problem of making fuel changes to give the lowest risk emissions will require the many competing interactions in fuel systems to be understood so the best, most environmentally benign, solution can be achieved.

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