The Use of a Low Frequency Vibration Signal in Detecting the Misfire of a Cylinder of an Aircraft Piston Engine

The following article describes the low frequency vibration analysis of aircraft piston engine Rotax 912 ULS. The results are based on the vibration signal made by the engine in the frequency range up to 400 Hz measured on the engine block in three axes. The aim of the research was to determine the method of detecting the misfire of individual cylinders based on the power spectrum of the selected frequencies analysis. Frequencies resulting from the periodicity of engine operation related to the frequency of the work cycle, rotational speed and ignition frequency were considered for the analysis. The tests were carried out in one point of operation. The highest levels of changes were recorded in the Y axis - the axis of piston movement. It was shown that the vibration level changes after switching off one of the cylinders. An indicator describing the vibration level was developed based on the value of amplitude of the power spectrum of vibrations two selected frequencies and it was shown that on its basis it is possible to detect misfires of individual cylinders. It was proven that it is feasible to use this method to diagnose misfire with the identification of a particular cylinder.