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Environmental regulations are going to put severe demands on the oil industry for improving fuel quality. Awareness about increasing contribution of automotive vehicles to air pollution particularly in major Indian cities has led to the enforcement of more and more stringent vehicle emission regulations. Emission norms to be applicable from April 1, 2000 for gasoline and diesel vehicles call for major changes in the engine design and a substantial improvement in the present level of fuel quality. Various fuel characteristics significantly affect the vehicle emissions. Main properties of attention are content of lead, sulphur, benzene, aromatics, olefins and oxygenates, and fuel stability in case of gasoline; and cetane number, distillation range, oxidation stability, aromatics content, sulphur content and density in case of diesel fuel. This paper presents a review of the worldwide trends in fuel quality changes for meeting emission norms.

Available information in the literature has been reviewed to understand the effect of gasoline composition (olefins, aromatics and benzene) on the exhaust emissions from two and four wheeled vehicles. Studies show that isolating the effect of an individual compositional characteristics may be difficult. Aromatics in the exhaust could be correlated with the aromatics in the fuel. The benzene and toluene fractions in the exhaust were sometimes more than in the fuel because of dealkylation of higher alkyl aromatics. The olefins fraction in the exhaust were also observed to be more than in the fuel. The olefin fraction was noted to be directly proportional to the sum of olefins and paraffins in the fuel, and, inversely proportional to the aromatics. Exhaust emissions of benzene may be due to benzene content in the fuel or benzene formation during combustion or over the catalytic converter due to dehydroalkylation of the alkyl benzene.