Similar to vehicle engines, marine engines are required to realize zero emissions of poisonous gas like SO_x and GHG like CO_2. Therefore, fuels used for future engines will be needed to reduce the content of sulfur and carbon. Under such requirements, the lubricated sliding interface of a piston ring and a cylinder liner often suffers damage, such as excessive wear and scuffing failure, caused by changes in lubrication condition due to in-cylinder combustion and/or fuel-derived substances mixed in the lubricating oil. Given this, appropriate measures are eagerly required to prevent such damage. The thermal friction characteristics of the ring / liner interface under the mixed / boundary lubrication regime during engine break-in procedure are thought to be almost the same as those of cam / tappet under the boundary lubrication regime when using low-viscosity lubricating oil with additives, which was the key subject the authors investigated in their previous study. By analyzing changes in frictional shear stress and the surface temperature and examining a correlation between them, just like the Arrhenius’ equation, it has been clarified that the temperature of the interface displays lubrication functions that can reduce friction, wear and scuffing. Concerning the viscosity and additives of the lubricating oil, the surface roughness of the interface, the ring profile, the contact pressure and the sliding velocity the authors have also investigated how the surface temperature contributed to reducing friction. To this aim, they analyzed the ring / liner data measured with a rotary disk type reciprocating friction test apparatus, which makes it possible to detect the friction force and the ring temperature under the same contact pressure and sliding velocity as those during engine break-in procedure.

  The CCAI (Calculated Carbon Aromaticity Index) is calculated from the density and kinematic viscosity of a marine fuel to evaluate the ignitability of the fuel. The CCAI is a useful index for marine residual fuel with few measurable physical properties. However, when a fuel ignitability test is performed using the FCA (Fuel Combustion Analyzer), the measured ECN (Estimated Cetane Number) is not always in a correlation with the calculated CCAI. In this study, we propose a real-fuel modeling method and a technique to estimate the proportion of hydrocarbons in this model fuel. The fuel model was constructed with a mixture of hydrocarbons with known physical properties, and a model hydrocarbon whose molecular structure is composed of polycyclic aromatics and alkyl groups so as to satisfy the mixing rule. As a result of predicting the hydrocarbon component ratios of each fuel by using its measured cetane number, density and kinematic viscosity, we found that the component ratios were different among each fuel even in the same CCAI. It was assumed that fuels with high ECN are high in n-alkane, i-alkane (branch 1) and alkylbenzene, and low in i-alkane (branch 3-7).