A research DI Diesel engine has been constructed for the optical investigation of in-cylinder flow fields, spray, combustion and emissions phenomena. This ported engine, built on a CFR crankcase, permits complete optical access to the combustion chamber which is located in the head of the engine. In the present study, combustion chambers with square and round cross-sections were used, and non-swirling and swirling flows were investigated. The flow fields for the various configurations were measured in the motored engine using laser Doppler velocimetry (LDV) to establish the conditions that existed prior to fuel injection. High speed movies were used to observe the spray and combustion processes with and without swirl in the two combustion chambers. Distinctly different patterns of the spray plumes and visible light emission are observed for the two flow conditions, but no major differences were observed with changes in bowl geometry under similar flow conditions.