Study On Hazard Evaluation For Dual Fuel System Of MAN B&W ME-GI Engine

Because of the high efficiency and increasing reliability of fuel engine, it has been adopted by more and more LNG vessels as primary power plant. Since 2003 MAN B&W Company defined the conception of ME-GI dual fuel engine, the shipping industry began to discuss its feasibility of applying it to LNG vessels. ME-GI can make most use of BOG from LNG liquid tank, which has strong attraction for the shipping industry when the present fuel oil price is at high level. Because the natural gas is required to be used in the ship's machinery space, therefore the safety of using ME-GI fuel engine on LNG vessels is worth to be further discussed.When MAN B&W Company put forward the design scheme of ME-GI dual fuel engine, they proposed to identify its risk by Failure Mode and Effect Analysis (FMEA) method. During the risk identification process, another risk assessment approach-Risk Priority Number (RPN) method is needed. But such risk assessment methods combining FMEA with RPN, could not be realized quantitatively, so to use fuzzy comprehensive evaluation on this basis to judge the overall risk degree of ME-GI dual fuel engine accurately.Taking MAN B&W6S70ME-GI dual fuel engine as an example and on the basis of further study of the dual fuel engine, firstly this thesis sets up the failure model of this fuel engine' s fuel system and gas system. For fuel system, FMEA is mainly conducted based on its functions, and according to RPN method expert census tables are made, RPN value of each failure mode is obtained; for gas system, because of the lack of its related application experience, FMEA is carried out based on gas leakage and its lead to ignition and explosion.Secondly, based on the above result of failure mode and effect analysis, transform the data investigated into the fuzzy matrix that is related to the corresponding failure mode by combining the experts census results, thus carry out the fuzzy comprehensive evaluation on the risk degree of MAN B&W6S70ME-GI fuel gas system. After the above risk assessment has been done, we come to a conclusion that the whole dual fuel system of MAN B&W6S70ME-GI fuel engine is in good condition, but certain risk exists. Daily maintenance and management of high-pressure fuel pumps, oil injectors and heavy oil separators in fuel system need to be put an eye on; the risk of ignition and explosion caused by gas leakage into the ship's machinery space is also identified in detail, and then this thesis puts forward some suggestions on the design and daily management of gas system, thus improving the reliability of this diesel engine's dual fuel systems and ensuring the safe operation of LNG vessels.