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The operation of Diesel engines now days has demanded higher thermal efficiency and lower emission to achieve low cost operation and to comply emission regulation. It is well known that the start of combustion will decide the quality of combustion. The start of combustion can be used to analyze the injection process and also the combustion process. In this work, wavelet analysis is used to determine the start of combustion will be discussed in this paper. The common method to determine the start of combustion is normally using the second order derivation of combustion chamber pressure. This method is used to validate the results from wavelet analysis. The experiments are conducted using several types of Diesel engines operated in several operating conditions. The results show consistently coincidence between start of combustion determined from pressure transducer and determined from the wavelet analysis in any rpm and load.

This paper describes a preliminary study to determine the correlation between the vibrations measured by accelerometers mounted on the engine surface with engine components as the sources. To obtain the signature of vibrations generated by engine components only, the crank shaft was rotated by an electric motor through a V-belt Compression and combustion were alleviated by removing the sparkplug. By using a Multichannel Spectrum Analyzer for converting the vibration signal into frequency domain, it was found that source of vibration such as gear pair, chain-sprocket, gudgeon pin and abnormal lubrication could be identified through the measurements.

A noise analysis based on coherence method has been developed and utilized as a diag - nostic tool for defect detection of a gear box. A case study has been carried out on a multiple reduction gear box and the emitted noise is measured during normal working environment thus the signals are subjected to external disturbing noise. Using the coherence method, the original signals are identified and further analysis is carried out using enhanced Campbell as well as Order-ratio diagrams. The results show that the coherence method is a powerful tool in noise analysis.

An experimental study has been carried out on a transmission system which consists of a pair of spur gears mounted using ball bearings on a steel frame and rotated by a frequency controlled A-C electromotor. The vibration sources among the rotating components of the system have been investigated using Campbell diagram technique and its influence on the frequency spectrum at the measuring points located on the frame has been identified. Harmonic as well as random excitation techniques have been conducted to reveal the transfer-function and the frequency spectrum at those measuring points. It is observed, for low frequency range (up to 125 Hz) similar transfer functions are obtained through out the measuring points. On the other hand for high frequency (above 125 Hz) the transfer functions are significantly influenced by the local propagation path.

Several transmission gear boxes of small size transportation vehicle have been investigated using noise analysis based on Campbell as well as Order-ratio diagram. The emitted noise signal is analyzed digitally using Spectrum analyzer and computerized data processing is performed to identify noise sources of the rotating elements. For this particular gear box, the results show the noise sources are mainly from the rotating shafts.