On the measurement and modelling of high pressure flows in poppet valves under steady-state and transient conditions
MohrStephan
ClarkeHenry
GarnerColin
RebeloNeville
WilliamsAndrew
ZhaoHuayong
2017
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 whilst maintaining realistic
in-cylinder transient pressure profiles by simply using a fixed area outlet orifice. A one-dimensional modelling 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 steadystate
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: 1. For a given valve lift, the steady-state flow coefficients fall by up to 21
percent with increasing cylinder/manifold pressure ratios within the measured range given
above; 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.