Analysis of in-cylinder turbulent air motion dependence on engine speed

In-cylinder cycle-resolved LDV measurements have been made in a diesel engine having a high-squish re-entrant combustion chamber with compression ratio of 21:1. The engine has been motored in the range of 1,000 to 3,000 rpm thanks to the use of self-lubricating seeding particles. Conventional ensemble- averaging and filtering techniques have been used for analyzing instantaneous velocity data obtained at two points along a diameter located in a horizontal plane at 5 mm below the engine head. The dependence of the mean motion and turbulence on engine speed has been evaluated. The effect of cut-off frequency selection on turbulence values has been also analyzed. Moreover, the Kolmogorov's -5/3 power domain has been investigated in detail by spectral analysis on the instantaneous velocity data. The results show the almost linear dependence of mean motion and turbulence on engine speed in the range investigated. The selection of cut-off frequency has a greater influence on the high frequency fluctuation at lower engine speeds than at higher ones. The spectrum analysis of the instantaneous velocity data has shown that in the medium and high frequency range the data do not follow the Kolmogorov's -5/3 law, that is characteristic of isotropic turbulent flow.