Reductions in fuel consumption and pollutant emissions from direct injection diesel engines are important issues in engine research. To achieve these reductions, rapid and better fuel air mixing is the most important requirement. The mixing quality of diesel spray with air is generally improved by selecting the best injection parameters and improving the characteristics of air movement in the combustion chamber. The shape of the combustion chamber can also help to form better mixtures. In this study, improvement in mixture formation was attempted by changing the combustion chamber geometry.The fuel spray development was visualized from two directions in an actual engine with a transparent cylinder and piston arrangement. The place where spray impinges, the distance from impinging wall to nozzle tip, and the shape of the chamber entrance and bottom were varied to determine their effects on the fuel spray development in the combustion chamber.It was found that a re-entrant type combustion chamber with round lip and round bottom corners provides better air and fuel distribution than a simple cylindrical combustion chamber. From the results modifications of the available empirical equations for calculating the spray path length and the area where spray spreads were attempted.