Additional ICU work may be needed to keep some older ships running constantly on VLSFO. File Image / Pixabay
As many as a few hundred large ships may need some engine upgrade work to cope reliably with the new very low sulfur fuel oil (VLSFO) blends, according to engineering company Wärtsilä.
The shift in the dominant bunker fuel from high sulfur fuel oil (HSFO) to the new 0.5% sulfur VLSFO products as part of the IMO 2020 change has generally been a surprisingly smooth transition so far, with most ships changing fuel towards the end of last year and few yet reporting significant problems.
But the change has involved a big shift in the viscosity of fuel that engines have to handle -- Integr8 Fuels saw VLSFO average viscosity at 100 CST in March, down from the old 380 CST HSFO specification -- and some older engines may still need modifications to help them cope with the less viscous new blends.
The lower-viscosity fuels may cause leaks in the fuel system in pipe seals that were designed to work with HSFO, according to Wärtsilä.
"Earlier generation Injection Control Units (ICU) were designed for operation with residual fuels," Andreas Wiesmann, a general sales manager for two-stroke engines at Wärtsilä, told Ship & Bunker by email last week.
"However, since the global sulphur cap came into effect from 1st of January 2020, some main engines have encountered operational issues to the fuel injection components due to continuous usage of the new compliant fuels with lower viscosity."
An Abrupt Halt
"The implications of using low viscosity fuel in the ICU vary depending on engine type and ICU type," he said.
"On small bore engines starting difficulties were often reported due to worn injection control valves (a part of the ICU), whereas for big bore engines more exhaust gas temperature alarms are reported caused by premature wear of the ICU valve seat causing uncontrolled injection in severe cases (i.e. the fuel continues to be injected after regular injection period).
"Moreover, in case there is increased deformation on the high-pressure pipe sealing due to repeated maintenance or ageing, then the risk of fuel leakage incident will increase, which can bring ships to an abrupt halt."
The ICU upgrade work that Wärtsilä is suggesting may be needed is designed for with Wärtsilä RT-flex96C-B and RT-flex84T-D two-stroke engines.
About a quarter of the 1,100 or more commercial ships with RT-flex engines have these specific types of engine and could benefit from the upgrade, Wiesmann said. These ships are mostly container ships and large tankers.
The work can be completed during scheduled maintenance at port and should not require dry-docking.
"Apart from some additional modification costs, the upgrade is in line with the usual ICU maintenance costs," Wiesmann said.