Experimental investigation of swirl motion of in-cylinder flow in CI engine under firing condition due to preinjection using PIV and POD techniques

The swirling motion of the intake air creates a flow field within the engine’s cylinder, which enhances the mixing of air and fuel, as well as combustion and emissions. Moreover, swirl formations in the cylinder and their subsequent breakdown into turbulence kinetic energy reflect the importance of in-cylinder flow structures. This study combined the PIV technique with the POD method to investigate the velocity fields in a single-cylinder diesel engine. The experiments were conducted at various pressure conditions and different engine rpm. Based on the obtained results, the average flow velocities from expansion to exhaust strokes were reduced in comparison with intake strokes. In all engine pressure and speed conditions, compression and exhaust strokes showed a significant change in flow patterns with changes in pressure and speed. At various crank angles, the POD modes demonstrated flow properties of the swirling motion, along with a dissimilarity feature and evolution of the in-cylinder flow.