The fluid motion in an internal combustion engine is induced during the induction process and later modified during the compression process. There are various methods to improve the efficiency of engine such as super charging, turbo charging, varying stroke length, varying injection pressure, fuel to air ratio, additional strokes per cycle and so on. Many of them require additional design (stroke length, injection pressure etc.,) and some of them lead to increase environmental effect. The objective of this study is to compare the performance and emissions of circular and nozzle guide vanes air swirl generating devices of a Compression Ignition (CI) engine. The investigation is performed by an experiment on a four- stroke single-cylinder diesel engine test bed with two different types of guide vane profiles, were installed at the downstream of the air intake manifold. There by increasing the mixture quality of air & fuel in the combustion chamber before the initialization of ignition. The engine load tests were carried out at different loads with and without air swirl devices. The emissions from the engine were also tested before and after the setup installation to estimate the environmental effects.