The influence of Swirl Control Strategies on the Intake Flow in Four Valve HSDI Diesel Engines

Standard design practice usually adopts steady flow tests for addressing optimisation of the intake valve-port assembly. Recently, with more user-friendly CFD tools and with increased computer power, intake stroke simulations, handling both piston and valves motion, have become practical. The purpose of this paper is to compare the design guidelines provided by the standard steady flow tests (both experimental and numerical) and the information coming from a CFD-3D intake stroke analysis. Reference is made to a four valve HSDI Diesel Engine.Three swirl control strategies are investigated. It is supposed that one intake valve is kept closed, while the other one operates normally (fist strategy). The second strategy consists in a 50% reduction of the lift of both valves. Finally, the third possibility is the blockage of one intake port by means of a simple butterfly valve.While the steady flow tests (both numerical and experimental) indicate that the first and the third strategy massively enhance the swirl intensity in comparison to the baseline (+75 %, according to experiments), intake stroke calculations show an almost null advantage. Furthermore, the actual in-cylinder flow field presents complex patterns that cannot be described in terms of Swirl Ratio.