Usman Muhammad, Product Manager - Fuel Advisory at LR, analyses issues and explores actions to avoid costly failures associated with fuel transitions.
Marine diesel engines have been the prime movers for merchant ships for more than a century. They are robust, reliable and have proven their worth across hundreds of thousands of nautical miles. But with more attention now focused on fuel oils and engines as the world fleet transitions from HSFO (high sulphur fuel oil) to VLSFO (very low sulphur fuel oil), a lack of effective monitoring may be storing up problems for the future.
Around 84% of the world fleet, ships >10,000 gross tonnage, uses the crosshead type low speed, two-stroke engines for main propulsion. The main advantages of these engines include being reversible, uniflow-scavenged, turbocharged and able to provide thermal efficiency and reliability through having fewer moving parts. Moreover, the robustness of these large, low speed engines has always enabled them to burn cheap heavy fuel oils of varying quality.
Despite the successful operation of these engines over the past few decades, there have inevitably been incidents of loss of propulsion due to main engine failures. These incidents, although few and far between, represent a significant economic loss for ship operators – not only from direct maintenance costs, but also from indirect costs such as off hire and port fees that can run into millions of dollars. In its 2018 annual report, the Swedish Club reported that the cost of machinery claims for the period 2015-2017 was around USD 384 million. Main engine damage was the most expensive category, accounting for 34% of total machinery claims.
Although there has been continuous efforts to improve the diagnostic capability to detect incipient failures before they occur, more awareness is needed as to the importance and benefits in utilising available machinery condition monitoring tools. Research indicates that only 5% of the shipping industry uses some form of condition monitoring for maintenance management. When compared to other industries, this figure is quite low.
Determining and optimising the combustion performance within large two-stroke engines holds the key to improving overall engine efficiency. Fuel combustion is a complex chemical/physical reaction and has been an area of intense research over the years. However, inconsistency in the composition of residual marine fuels makes it very difficult to predict engine component wear rates and failure mode.
Since the implementation of MARPOL Annex VI regulation 14.1.3 from 1st January 2020, Lloyd’s Register FOBAS have seen an upsurge in combustion-related incidents resulting in cylinder liner and piston ring damages of large two-stroke engines during the period that the world fleet started transitioning from high sulphur fuel oil (HSFO – max 3.5%) to very low sulphur fuels (VLSFO – max 0.50%).
There are several factors which can influence the combustion in an engine, and a holistic approach is needed to evaluate all the operational information to connect the dots. For example, in the recent spate of cylinder component damage incidents reported by ships since the beginning of this year, a clear contributing factor was the change of fuel oil from HSFO to VLSFO. However, our investigations revealed that poor fuel ignition and combustion characteristics were unlikely to have been the main reason for these incidents. In fact, most VLSFO showed better ignition quality compared to HSFO during lab testing.
Further analysis identified that damage was caused by a number of influencing factors which include any combination of the following: the applied cylinder oil quality; poor maintenance; lack of operational adjustments; excessive or insufficient cylinder oil feed rate; not following OEM guidance on ring selection.
This combination of influencing factors highlights the critical importance of utilising a multifaceted approach in which ship operators consult engine manufacturers and fuel testing and advisory services, and ensure best practice approaches are followed on-board.
In light of the diversity of composition and varying fuel quality of these VLSFOs, the use of an appropriate condition monitoring tool could further reduce the risk of breakdown scenarios through the diagnostic capability of picking up any incipient failure.
Here at LR, FOBAS provides lube oil analysis and, for more comprehensive engine condition monitoring, our FOBAS Engine Assessment Programme (FEAP) can be used to monitor two-stroke engine performance. Through regular sampling and data collection, the FEAP service is specifically designed to highlight and alert the ship to the health of components within the combustion chamber in order for the on-board staff to take appropriate mitigating action – to avoid the potential operational and commercial issues.
Please contact us for further information. One of our experts will be pleased to discuss the process and further explain the FEAP service.
3. IMarEST conference (2015) London. https://www.imarest.org/conference-proceedings