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Multiple injection tests were carried out using a 1.2-liter 4-cylinder Ford DIATA (Direct Injection Aluminum Through-bolt Assembly) engine at various operating conditions. The results were simultaneous reductions in NOx and soot emissions. An engineering model based on characteristic times, with consideration of both thermal and N2O formation kinetics, is utilized to gain insight into the reasons for NOx reduction due to multiple injections. Stoichiometric combustion is assumed for NO formation. In this research, normalization and parametric studies are used to study the effects of injection timing, fuel quantity per injection pulse, and injection rate on NOx emissions. NO formation is reduced by modifications that lower stoichiometric flame temperature at the start of combustion of fuel injection pulses or decrease time spent by a fluid element in the stoichiometric zone.