An experimental investigation on two different methods for swirl induction in a multivalve engine

This paper describes an experimental investigation aimed at comparing the swirl effect induced by unbalancing the mass flow through the two intake ports of a multivalve engine head using two different methods: the first one reduced the curtain area of one of the intake valves [different lifts (DL) method]; the second one adopted a sluice-gate-shaped valve, installed upstream of the intake valves [swirl control valve (SCV) method] in order to cause a pressure drop. A steady-flow test rig (equipped with instrumentation for the discharge coefficient and swirl intensity measurement) was realized in order to compare and evaluate the results of both methods and determine their respective validity and limitations; the procedures used for both experimental methods are discussed in detail. The flow characteristics were analysed through changes of lift difference or SCV position; it was found that both DL and SCV methods are effective in swirl induction but the DL mechanism, acting on the valve curtain area, is more effective in flow unbalancing between intake ports, since the flowrate depends linearly on the curtain area, The SCV method, instead, controls the port flowrate, inducing a localized pressure drop, whose intensity depends on the flow velocity in a non-linear manner. For this reason the SCV method can achieve strong swirl intensity only with high obstruction levels, in a narrow regulation window close to full-obstruction conditions.