Thermal and elemental analysis of the combustion chamber deposits in a large-scale two-stroke marine diesel engine

It is of significance to understand the chemical content of carbon deposits in the large-scale two-stroke (LSTS) marine diesel engine because of adverse effect on the engine performance, oil consumption and emissions. In this work, two different combustion chamber deposits in an LSTS marine diesel engine were studied using thermogravimetry analysis (TGA), elemental analysis (EA) and synchrotron X-ray fluorescence (SXRF). One was on the piston top and the other on the piston land, termed PTCD and PLCD, respectively. For the PTCD sample, the 97% residue in the TGA and 1.4% carbon content in the EA indicated the main compositions of PTCD were metal salts or oxides and ashes, significantly different from the previous findings of the highest carbon content in deposits from the small four stroke engines. The different chemical content between PTCD and PLCD implied higher thermal load in the LSTS marine diesel engine led to a nearly complete thermal decomposition of PTCD. The higher calcium content in PTCD and PLCD indicated the additives of cylinder oil should be the main source of metal content of PTCD and PLCD. Calcium distribution in the SXRF results was indicative of the potential layered structure in PTCD and PLCD. In addition, the appearance of iron on the surface against the piston in PTCD and PLCD indicated iron oxides formation between carbon deposit and piston materials.