Study on In-Cylinder Flow of Direct Injection Diesel Engine by LDV Measurements: (Turbulence Analysis at Low Sampling Rate with Non-Uniform Time Intervals)

The authors have developed a method to analyze the turbulence scale accurately from the descrete data, which are usually obtained by LDV measurements, at low sampling rate with non-uniform time intervals. In this method, the turbulence correlation is calculated from the data of many engine cycles, and successively the turbulence spectrum is calculated from the inverse Fourier-transform of the turbulence correlation. The reliability of this method is confirmed by the model data sampled randomly on a sinusoidal process, and by the data measured in the cylinder of a motored diesel engine having a direct injection system. Furthermore, it is clearly shown that the spectrum in the frequency range higher than the Nyquist frequency defined by the mean data rate can be analyzed by this method, and that it is not necessary to change the range of frequency analysis despite a little variation of mean sampling rate.