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This paper is closed access until 7th March 2018.Flow coefficients of intake valves and port combinations were determined experimentally for\uda compressed nitrogen engine under steady-state and dynamic flow conditions for inlet\udpressures up to 3.2 MPa. Variable valve timing was combined with an indexed parked piston\udcylinder unit for testing valve flows at different cylinder volumes whilst maintaining realistic\udin-cylinder transient pressure profiles by simply using a fixed area outlet orifice. A one-dimensional modelling approach describing three-dimensional valve flow characteristics has\udbeen developed by the use of variable flow coefficients that take into account the\udpropagation of flow jets and their boundaries as a function of downstream/upstream\udpressure ratios. The results obtained for the dynamic flow cases were compared with steadystate\udresults for the cylinder to inlet port pressure ratios ranges from 0.18 to 0.83. The\uddeviation of flow coefficients for both cases is discussed using pulsatile flow theory. The key\udfindings include: 1. For a given valve lift, the steady-state flow coefficients fall by up to 21\udpercent with increasing cylinder/manifold pressure ratios within the measured range given\udabove; 2. Transient flow coefficients deviated from those measured for the steady-state flow\udas the valve lift increases beyond a critical value of approximately 0.5 mm. The deviation can\udbe due to the insufficient time of the development of steady state boundary layers, which\udcan be quantified by the instantaneous Womersley number defined by using the transient\udhydraulic diameter. We show that it is possible to predict deviations of the transient valve\udflow from the steady-state measurements alone

On the Measurement and Modeling of High-Pressure Flows in Poppet Valves Under Steady-State and Transient Conditions