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Locomotive Diesel Engine Stress Wave Analysis
Andrew Chater MSc
PCMSEng UK, Darland House, 98 Hermitage Road Saughall, Cheshire. CH1 6AQ andy@pcmseng.co.uk

Keywords: Vibration, Stress wave, Diesel Engine

Abstract
Vibration analysis on internal combustion engines poses unique challenges not ordinarily encountered on rotating machinery. Stress Wave Analysis for engine fault detection isemphasised in this paper. A time waveform consisting of peak values observed over sequential discrete time intervals is captured and subsequently analysed. The analyses are the (a) peak values (measured in g’s), (b) spectra computed from the peak value time waveform, and (c) the autocorrelation coefficient computed from the peak value time waveform. Samples of various faults are presented toillustrate the Stress Wave Analysis methodology. The classes of faults are (a) Over combustion, (b) Crank shaft, (c) Valve bridge, and (d) good cylinder. It is demonstrated that stress wave analysis make possible the identification of the defect and the severity of the defect.

Stress Wave Analysis methodology has been introduced for the analysis of impact like events and has proven to be an effectivetool for identifying bearing and gear defects. In this paper, the use of Stress Wave Analysis for diesel engine defect analysis will be demonstrated through examples which cover typical defects encountered with diesel engines. A very brief discussion on the basic concept and analysis will be presented in the next section. This will be followed by examples that cover specific engine componentfailures.

2 New Data types for analysis of engines
Historically Vibration analysis on internal combustion engines has always posed unique challenges not ordinarily encountered on rotating machinery. The general combustion engine has many forcing function sources - bearing configurations, shafts rotating at different speeds, crankshaft lobes being acted upon by pistons, pistons movingtranslationally, cams activating valve mechanisms, and the combustion of a volatile gas mixture. All of these forcing functions acting simultaneously produce a very complex frequency signature of the process. As a result, few of the harmonic relationships required for rotating equipment analysis are present in the internal combustion engine. Normal FFT analysis has been a good technique for detecting bearingwear and balance problems. Many failure modes of internal combustion engines may be detected using standard FFT techniques- main bearing wear, connecting rod bearing wear, cam bearing, crank balance, and shaft misalignment of connected equipment. Other common failure modes in the diesel engine have not been so easily detected by the FFT technique. These problems centre on valve train, bent rods,worn cams, weak Valve springs, injectors, worn valve guides, loose rocker arms, etc. Also, combustion problems have been considered difficult to interpret, such as knock caused by improper spark or injector timing and poor fuel. 2.1 Vibration signals A Normal Vibration Waveform & Spectrum has limited value for the assessment of combustion engine mechanical health. Impacts due to combustion,nonsymmetrical waveforms and

1 Introduction
As a result of the continuing trend towards deregulation across the rail industry, rolling stock owners, operators and maintainers face an increasingly demanding market environment where cost efficiency must combine with availability, reliability and safety. Rolling stock manufacturers are asked to provide more reliable locomotives designed to the highestlevel of maintainability. With increasing financial penalties should they fail to do so. The environment in which Locomotive Diesel engines operate is extremely hostile and failures can be catastrophic or at the very least expensive to resolve. As the condition of equipment operating in this hostile environment is not known it is very difficult to improve their reliability. Maintenance must...
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