Wavelet Analysis of In-Cylinder LDV Measurements and Correlation Against Heat-Release

Wavelet analysis was used to calculate turbulence and mean velocity levels for LDV measurements made in a four valve spark ignition engine. Five different camshafts were tested, and they produce significantly different flow behaviour. The standard cam gives tumble and with valve deactivation, swirl is produced. One camshaft with early inlet valve closing and two camshafts with late inlet valve closing were also tested. The wavelet toolbox for Matlab version 5.1 has been used for the wavelet calculations.

The wavelet technique produces both time resolved and frequency resolved velocity information. The results indicate some influence of the turbulence frequency content on the rate of heat release. Correlation against heat-release can be seen for different scales of turbulence. The breakdown of the tumble (low frequency turbulence) into high frequency turbulence can be seen clearly. This transition is not as clear with a swirling flow, where all frequencies are magnified equally at top dead center. The choice of wavelet does not have a major impact on the results.