Fuel-air mixing during the early period has a significant influence on the combustion and emission processes of small diesel engines where combustion duration is short. The mixture heterogeneity during the premixed phase influences the premixed burnt fraction and the peak rate of energy release. The premixed burnt fraction is affected by engine speed, air swirl and fuel injection. In diesel engines, injection parameters, piston configuration and induction swirl interact with each other and have an optimum condition for a better performance. The present paper is an attempt to investigate these effects using an improved existing analytical model. The results concerning the effects of swirl and injection conditions on fuel-air mixing pattern, the premixed mass fraction and the rate of energy release at the instant of ignition, and duration of combustion on engine combustion and emission characteristics are presented.