Onboard Fuel Oil Cleaning, the ever neglected process How to restrain increasing Cat-fine damages in two-stroke Marine Engines
Remains of Cat fines in the fuel oil entering the engine account for a considerable part of the wear of the combustion chamber components in twostroke engines. The attempt to lower the amount of cat fines in fuel oil bunkers by the ISO 8217:2010 to maximum 60 ppm has however not lowered the global average content. On the contrary, increased use of ECA fuel has lead to a significant increase in the number of cat fines related engine wear situations. Cat fines entering the engine create wear by means of socalled 3-part abrasion. The sliding surfaces made of cast iron are the most sensitive, as the cat fines has a tendency to embed into natural porosities of the cast material structure and create wear on the counterpart. Thereby cylinder liners, piston ring grooves and piston rings become the most affected components of twostroke engines. It is rare that cat-fine related damage is seen on the fuel equipment due to the high hardness of those components. Recent statistic, involving 165 high cylinder and piston ring wear cases, where replica technique have been used detecting cat fineparticles embedded in the liner surface, showed cat fines being the reason in 86% of the cases. This investigation has also shown that even small cat fine particles below 10 micron contribute to the wear. Analysis results of the HFO bunkered in most of the high wear cases showed that the vessels in question had bunkered fuel oil within the limits of the ISO 8217:2005 specification. Consequently, the cause of the high wear may be found in either too low separation efficiency onboard, by settling and accumulation of cat fines in the different tanks onboard or a combination of both. This highlights the need of an approved method specifying separator size and efficiency, e.g. Certified Flow Rate (CFR) or similar methods. It also calls for regular checks of the onboard separation efficiency, e.g. by participating in a Fuel System Check (FSC) program. Commercial methods such as Cat fines Size Distribution (CSD) screening adds an extra dimension by evaluating the particle size of the cat fines. A severe cat fines attack has been monitored by measurements of cylinder liner and piston ring wear through online drain oil analysis. The results showed that the wear dropped from an extremely high to normal level few days after the supply of cat fines had stopped by changing of fuel and after manual cleaning of the tanks. The conclusion is that cat fines damage over a long period of time is the result of a continuous flow of cat fines led to the engine, and that the wear is not stopped until manual cleaning of a contaminated system (including settling and day tanks). Proper lay-out of tank and pipe connections of the fuel oil cleaning systems onboard can prevent cat fines accumulation by continuously cleaning the tank bottoms. This in connection with optimised flow rate through the cleaning system, taking advances of the fact that marine engines mostly is operated at part load, may give a significant improvement of the cleaning efficiency. New systems including settling- and day tank lay-out, recirculation pipe connections with flow measuring device and dynamic control of the separator supply pumps are presented in the paper. Technologies, such as FSC, CSD, LinerScan and Cat Guard, have been used in combination with ’COCOS Engine Diagnostic System’ to evaluate the correlation between cat fines concentration and engine wear rates as well as the need to improve the fuel cleaning efficiency onboard. The paper will demonstrate that the risk of cat fines related wear can be significantly reduced by ensuring optimized fuel system treatment, by introducing a new fuel cleaning system layout, by automatic control of the cleaning flow rate and by intensified monitoring of the fuel treatment efficiency.
Henrik Rolsted Rojgaard Charlotte Jensen Ole Englund Mats
MAN Diesel and Turbo,Denmark DNV Petroleum Services,Singapore NanoNord,Denmark Alfa Laval Tumba AB,Sveden
国际会议
上海
英文
1-13
2013-05-13（万方平台首次上网日期，不代表论文的发表时间）