Study on In-Cylinder Flow of Direct Injection Diesel Engine by LDV Measurement

Abstract

Swirl, turbulence and the cyclic fluctuation have been examined using LDV in a motored direct injection diesel engine with a spiral port, a troidal piston cavity and a bore of 102 mm. Measurements were made at a low engine speed of 600 rpm at nine points along a cylinder diameter. The authors have developed a new method to analyze turbulence accurately even under the low data rate condition by introducing a concept of confidence interval. It has been clearly shown that there exists a longitudinal vortex in the piston cavity, the tangential velocity distribution shows a forced vortex pattern, and the swirl ratio increases rapidly in the piston cavity. And turbulence in a compression stroke was not always uniform in the cylinder, but in-cylinder averaged turbulence and the cyclic fluctuation were almost the same between the tangential and axial components.