The Effect of Valvetrain Configuration on the In-Cylinder Jet Structure and Flow Resistance of a Piston Engine Under Steady-Flow Conditions (An Experimental Study Using the Particle Image Velocimetry Method)

The aim of this study was to experimentally investigate the effect of the intake valve lift and the number of active valves on the in-cylinder jet structure and flow resistance of a piston engine under steady-flow conditions over a wide range of air flow rates using Particle Image Velocimetry (PIV). The experiments were performed on an optical model of a piston engine cylinder equipped with a transparent cylinder and a valvetrain with two poppet valves. The model has no moving piston, and the measurement plane corresponds to the bottom dead center position of the prototype engine. The valve lift was varied within the range 0–12 mm, and either one or both intake valves could be activated, thereby replicating the geometry of a naturally aspirated spark-ignition gasoline engine with a bore/stroke ratio of 82/71. High-resolution flow-field images were acquired by PIV in two mutually perpendicular cross-sections at volumetric flow rates of 50–113 m3/h, with local flow velocities in the measurement plane ranging from 15 to 55 m/s. The results are discussed in terms of the jet structure, the vortex formation intensity, the turbulence intensity and the size of low-velocity regions. They characterize the flow resistance of the intake tract for each configuration. Numerical simulations of the engine working cycle were performed in Diesel-RK to complement the experimental data. Simulations were performed for the symmetric valve configurations at crankshaft speeds of 1000, 3000 and 6000 min−1. The calculated air flow rates ranged from 16.8 to 124.5 m3/h, thus covering the experimental range of 50–113 m3/h. The optimal valvetrain configuration among those tested depends on the airflow rate under steady-flow conditions. The single valve with a 6 mm lift provides the lowest flow resistance and the most uniform jet structure among the configurations tested at 50 m3/h. The single 6 mm lift and the asymmetric 6/12 mm configuration give comparable results at 79 m3/h. The asymmetric 6/12 mm configuration is the most effective at 97 m3/h. Two valves fully open to 12 mm provide the most uniform filling at 113 m3/h. The simulation reproduces the same general trend for the symmetric configurations as the crankshaft speed increases from 1000 to 6000 min−1.