This paper examines velocity averaging within Spark-Ignition (SI) engines,
a non-stationary system. Comparison is made between the mean and turbulence
velocities found from (a) Ensemble, (b) Cyclic and (c) Wavelet-based avera
ging. The various methods of extracting turbulence within this flow system
result in qualitatively similar average velocities; however, there are sign
ificant differences in the turbulence velocities and spectral content of th
e flow field based on the definition used. The differing interpretation of
turbulence results in a subjectivity to the physical understanding of the f
lows. The experience in extracting coherent structures in stationary turbul
ence suggests that wavelet analysis offers a unique insight that has applic
ability for engine studies.