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In-cylinder flow study is important to understand the fuel mixing , combustion and emissions in diesel engines. The initial flow pattern is set up by the intake stroke as free vortex and is subsequently modified during compression stroke as forced vortex. This paper deals with in-cylinder flow comparison for two different geometries of the intake manifold (Standard and Screw Threaded) of a single cylinder direct injection diesel engine. The scope of using screw threads is to improve the swirl motion of the intake air. Modified geometry involves an internal screw threaded intake manifold (forming a protrusion into the manifold) with defined pitch, cross-section and length of the helix path. An experimental study using a steady state flow rig(Paddle Wheel Type) has been performed on the standard geometry to obtain mass flow coefficient and swirl ratio. Steady state CFD simulations are performed on both the geometries using ANSYS FLUENT as solver and compared with the experimental data.

In-cylinder flow in diesel engines plays an important role in the combustion, thus affecting the emissions from the engine. Swirling flow inside the cylinder during intake and compression stroke is one of the important parameters that improve combustion. This paper deals with comparison between two different intake manifold geometries in a direct injection diesel engine in terms of their swirl generation mechanisms in the cylinder during suction stroke. The modified geometry involves a twisted tape inserted in the intake manifold for swirl generation. A three-dimensional numerical study of the flow behavior is performed using Computational Fluid Dynamics (CFD) and experimentally validated using a steady flow test bench. The effect of twist ratio on the swirl generation is simulated using CFD. The CFD study involves a transient case applied to a dynamic mesh which characterizes the downward movement of the piston during suction stroke.