Investigation on the microstructure and pore characteristics of carbon deposit on the piston top land of marine diesel engine using synchrotron X-ray microtomography

It is of significance that massive carbon deposit (CD) is observed in the combustion chamber of large-scale two-stroke marine diesel engine due to high thermal load, poor fuel quality, oil degradation and combustion and high particle emission. The structure and characteristics of CD have great influence on the engine performance and emissions. In this paper, we use synchrotron X-ray microtomography of Shanghai Synchrotron Radiation Facility to visualize the three dimensional structure of CD on the piston top land. Based on the quantitative image analysis, microstructure and pore characteristics of CD are investigated. The results show the CD thickness is around 1mm, half of clearance between cylinder liner and piston. However, the surface structure shows significant friction scratches, which suggests the oil film could be destroyed by the CD. The results of crackle distribution show that intensive crackle is located on the CD surface (inner and outer surfaces), while loosen crackle is found inside the CD. This implies that the crackle formation mechanism is different on the inner and outer surfaces. The analysis of pore connectivity indicated that most of cracks are connected, and the porosity is in the range between 10.9% and 12.8% in present experiments. In addition, small hole connected by cracks and the crackle could have impact on the absorption and desorption of unburnt emissions.

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