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

Abstract

Flow coefficients of intake valves and port combinations were determined experimentally for a compressed nitrogen engine under steady-state and dynamic flow conditions for inlet pressures up to 3.2 MPa. Variable valve timing was combined with an indexed parked piston cylinder unit for testing valve flows at different cylinder volumes while maintaining realistic in-cylinder transient pressure profiles by simply using a fixed area outlet orifice. A one-dimensional modeling approach describing three-dimensional valve flow characteristics has been developed by the use of variable flow coefficients that take into account the propagation of flow jets and their boundaries as a function of downstream/upstream pressure ratios. The results obtained for the dynamic flow cases were compared with steady-state results for the cylinder to inlet port pressure ratios ranges from 0.18 to 0.83. The deviation of flow coefficients for both cases is discussed using pulsatile flow theory. The key findings include the followings: (1) for a given valve lift, the steady-state flow coefficients fall by up to 21% with increasing cylinder/manifold pressure ratios within the measured range given above and (2) transient flow coefficients deviated from those measured for the steady-state flow as the valve lift increases beyond a critical value of approximately 0.5 mm. The deviation can be due to the insufficient time of the development of steady-state boundary layers, which can be quantified by the instantaneous Womersley number defined by using the transient hydraulic diameter. We show that it is possible to predict deviations of the transient valve flow from the steady-state measurements alone.

Performance of a novel liquid nitrogen power system

“…The specific work for compressed-air powered engines are slightly higher due to the absence of pumping losses from the pump, but at the cost of significantly lower volumetric energy density and cooling. In addition, the thermodynamic models did not take into account the pumping loss across the valve system at high inlet pressure, which was shown experimentally to be significant [16]. In this present article, a systematic study of the performance of an LN2 engine system with an integrated HEF subsystem is presented.…”

Fast simulation of railway pneumatic brake systems

“…Also, simplified approaches to obtain the time response of transient flows were developed, such as in Hullender, 16 where some results show to represent better the pressure response than the classical approach. For the valves, Mohr et al 17 modeled and measured the steady-state flow and transient flow through the poppet valve and obtained results similar to the measured ones. With the proposed method, they predicted the change from the steady-state flow to the transient flow for pressures up to 3.2 MPa.…”

“…For the valves, Mohr et al. 17 modeled and measured the steady-state flow and transient flow through the poppet valve and obtained results similar to the measured ones. With the proposed method, they predicted the change from the steady-state flow to the transient flow for pressures up to 3.2 MPa.…”

Design and development of a direct injection system for cryogenic engines

“…This work is an extension of the work done by Mohr et al 14 investigating high pressure flow through a poppet valve for the Dearman engine but with the use of liquid nitrogen rather than gas.…”