1 Heavy Fuel Oil (HFO) Operated Diesel Engine and Impacts of Sulphur Content on the Engine Life Saqaff A. Alkaff + ; Mohammad A. Mukbel ++ Abdullah Ba Wazeer +++ ; Saad Al Namori ++++ Abstract The type and quality of the fuel play an important and critical role in the combustion features and hence the energy produced. However, the complication and rapid reaction of this oxidation process limit the available knowledge of mediated products of this process. The products of combustion may dictate the life of the engine combustion chamber. However, there are many variables have direct or indirect effect to the process and the quality of combustion itself. This paper discusses one of the most recent operational problems encountered at the Rayyan Power Station, Al Mukulla, Yemen. Heavy fuel oil (HFO) is used to run the engines. After 17,000 run hours, a serious leak was observed on one of the engines cylinder heads. Thereafter, all the other engines show the same wear pattern. A severe corrosion was found around the exhaust valve seat. The material under and behind the valve seat was found corroded with a maximum depth of approximately 30 mm. The corroded area was not completely circular; at one point the corrosion caused a hole to the cylinder head wall into the cooling water space. A considerable effort was devoted to identify and to state the problem. However, the deterioration of the cylinder head valve seat pocket of the exhaust valve was found due to the reaction of sulphur with the water vapour, forming sulphuric acid as a corrosive agent. Several solutions were proposed or applied to overcome the problem. However, improving the fuel quality or fuel replacement is the most favourable.