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In India, two and three-wheelers constitute about 70% of the total in-use vehicle population and consume about 2/3rd of the total gasoline, rest of the gasoline being consumed primarily by the passenger cars. This paper presents the findings of an experimental study carried out on in-use gasoline vehicles, including two and three- wheelers and passenger cars. The gasoline fuels used for the study were equivalent to Euro-II, Euro-III and Euro-IV fuel quality specifications. The study analyzes the effect of improving the gasoline fuel quality on exhaust emissions from in-use vehicles.

An experimental study was conducted on in-use and new, Indian two-wheelers to study the effect of gasoline composition (olefins, aromatics and benzene) on exhaust mass emissions. Exhaust emissions of benzene were also measured. The study was conducted on six makes of new and in-use, two-wheelers consisting of popular 2-stroke and 4-stroke, mopeds, scooters and motorcycles. Three test fuels, a high olefin gasoline, a high aromatic gasoline and a Euro-III equivalent gasoline were used for the study. High olefin test gasoline contained 26.5% olefins, 10.3% aromatics and 0.3% benzene. High aromatic test gasoline contained 0.9% olefins, 61.9% aromatics and 1.5% benzene. Euro-III test gasoline contained 15.9% olefins, 37.4% aromatics and 0.9% benzene. Intake system deposit study was also conducted on 4-stroke motorcycles and two-stroke scooters having separate lubrication, using two fuels, i.e. high olefin gasoline and Euro-III gasoline, with and without the use of multi-function additives.

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.

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.