| While generic causes of combustion chamber deposit (CCD) formation have been investigated, the prediction of this growth in diesel engines has not been widely explored. Investigating three techniques for predicting CCD formation was the aim of the present study.; In the first phase of the current research, the engine-operating parameters that maximized CCD formation were selected based on factorial experimentation and analysis. These parameters were used in developing an empirical model that predicted the rate of CCD formation, as function of load, coolant temperature and the type of crankcase oil used.; In the second phase, two intrusive techniques for predicting CCD formation were investigated, whereby combustion cylinder instrumentation was required.; The first sensor investigated was a fast response surface thermocouple, because a similar spark ignition (SI) engine study showed that in-situ deposit thickness could be modeled through its use. The model is based on the premise that, as insulating deposit layers form, the temperature waveforms are damped and delayed. It was found in this study that the surface thermocouple was useful in detecting peak cylinder temperature delay and from this, a correlation was developed that predicts CCD thickness.; The second sensor investigated in this study was similar to a surface spark plug. The use of this sensor showed that there is a clear relationship between the electrical resistance of engine deposits and CCD growth rate and type. Several earlier studies confirmed that engine deposits resemble the properties of coal or carbon black material and that the electrical conductivity of carbon blacks is dependent on the relative concentration of aliphatic groups and poly-aromatics. In the current research, it was found that the electrical conductivity of deposits decreased as they formed. The voltage-drop profile across the deposits indicated increased deposit growth and a change in material structure. |
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