In this present work a study about influence of the air swirl in the cylinder upon the performance and emission of a single cylinder diesel direct injection engine is presented. In order to achieve the different swirl intensities in the cylinder, three design parameters have been changed: the cylinder head, piston crown, and inlet duct. In this way, the piston crown is modified i.e. alteration of combustion chamber to enhance the turbulence in the cylinder. This intensification of the swirl is done by cutting grooves on the crown of the piston. In this work three different configurations of piston i.e. in the order of number of grooves 3,6,9 were used to intensifythe swirl for better mixing of fuel and air and their effects on the performance and emission are recorded.