On-line power estimation of large diesel engines using acoustic emission and instantaneous crankshaft angular velocity

It is of interest to be able to gauge the power output of an engine from sensors that do not interfere with engine performance and are non-invasive. Acoustic emission (AE) analysis is one such technique, whereby information can be obtained from sensors placed on the external surface of the engine, requiring very little preparation. This paper shows that there is a strong relationship between AE energy and the variation of the instantaneous crankshaft angular velocity (ICAV) waveform over the engine cycle for a range of engine loads and that both types of measurement give a good indication of engine power on a 'per cylinder' basis. AE and shaft encoder signals were acquired from two large (>7 MW), low-speed, two-stroke, diesel engines over a range of power outputs. The ICAV waveform (inferred from the shaft encoder signals) for one engine cycle was found to give a resolution that showed compression and expansion strokes of each cylinder. The variance of this waveform was found to correlate well with the power output of the engine, a finding that is in accord with those of a number of other authors. Additionally, the AE energy associated with fuel injection/combustion during each cycle was also related to engine power output, a finding that has not explicitly been reported elsewhere. It is shown that, by combining both the AE and the ICAV data, and accounting for differences in engine specification such as number of cylinders, the observations of the two engines can be generalized, in that both the standard deviation in the ICAV waveform and the AE energy generated during the injection/combustion phase increase with increasing engine power output. This relationship can therefore be used to indicate engine power per cylinder and hence indicate whether cylinders are performing poorly. Provided that sufficiently robust sensors are available, such measurements could be made on-line and included in a preventative maintenance plan. © IMechE 2006.