Internal combustion engines have several vibration sources, such as combustion, fuel injection, piston slap and valve operation. It is necessary to separate the different vibration sources and then analyze each of them individually. This paper attempts to separate the vibration sources by blind source separation techniques and proposes a combination of the Blind Least Mean Square algorithm with a deflation method to separate several sources. The combined methods are first verified on simulated sources and then applied to engine signals. Separation results show that cylinder pressure consists of two sources—one is a smooth low frequency part due to compression and expansion caused by piston movement; the other is the high frequency part due to combustion.
Liu, X., Randall, R. B., & Antoni, J. (2008). Blind separation of internal combustion engine vibration signals by a deflation method. Mechanical Systems and Signal Processing, 22(5), 1082-1091. https://doi.org/10.1016/j.ymssp.2007.11.011