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A method to stratify the fuel-air mixture along the cylinder axis of engines is described. Axial stratification, with the richest mixture near the top of the combustion chamber and the leanest mixture near the piston top, was obtained by imparting swirl to the intake air and by injecting fuel into the inlet port just before the end of the intake stroke. Axial stratification was developed in both single and multi-cylinder engines over the range of operating conditions tested. A production four-cylinder engine modified to operate with axially-stratified-charge, showed: increased combustion stability and tolerance to dilute mixtures; decreased fuel consumption; similar HC and CO emissions; lower NO emissions and octane requirement when compared with the unmodified engine operated at the same overall equivalence ratio.