On the turbulence and cyclic variation levels in internal combustion engine cylinders

This paper describes an experimental investigation of the cyclic variations and instability of the jet flows in the cylinders of dual-intake port gasoline engines under both steady-state and motored engine conditions using laser-Doppler anemometry and spectral analysis techniques. The instability of the jet flows around the inlet valves was studied under steady state conditions. Cyclic variations observed near the centre of the cylinder were investigated by comparing turbulence and cycle-to-cycle variation levels within the region to those found within the intake jet of the motored engine. Spectral analysis techniques were also used to study velocity spectra at these locations. The results show that cyclic variations broaden the true turbulence levels substantially and should be taken into account when assessing the turbulent flow processes and related predictions.