Speed Dependence of Turbulence Properties in a High-Squish Automotive Engine Combustion System 960268

The variation of turbulent flow quantities with engine speed has been investigated in the combustion chamber of an automotive diesel engine with a high-squish conical-type in-piston bowl and one helicoidal intake duct, at speeds covering the wide range of 600-3000 rpm, under motored conditions. The investigation had the main purpose of studying the engine speed effect on the structure of both cycle-resolved and conventional turbulence over the induction, the compression and the early stage of the expansion stroke. The low frequency component of the fluctuating motion was also investigated. Although studies on the speed dependence of in-cylinder flow properties have long been carried out under motored conditions, some of them are limited to very low engine speeds, some others refer to flat-piston engines with a pancake-type combustion chamber, or to shallow in-piston bowl engines, while the few related to high-squish reentrant in-piston bowl engines are restricted to a narrow crank-angle interval, and also to a turbulence frequency content significantly reduced by limits in the velocity-data acquisition rate.

A sophisticated HWA technique using single- and dual-sensor probes was here applied for in-cylinder velocity measurements. New results on engine-speed dependence of in-cylinder turbulence statistical properties, such as intensity, probability distribution, time-correlation and frequency-spectral structure, were obtained for the practical speeds of 600, 1000, 1500, 2000, 2500, and 3000 rpm, at different locations along the injector axis.