New methanol two-stroke engines gain from service experience

Paul Gunton
ShipInsight

02 September 2019


Modifications to MAN Energy Solutions’ methanol-fuelled two-stroke diesel engine design have made it simpler to build, install and maintain, according to Kjeld Aabo, its sales director for new technologies.

He was comparing the engines installed in two new methanol tankers for delivery to Swedish owner Marinvest for operation by Waterfront Shipping of Canada with those fitted in seven vessels delivered in 2016 and operated by the same company. In July, ShipInsight included a brief overview of how those engines were developed from the engine designer’s ME series to mark their reaching 50,000 hours of operational experience with the fuel.

By the time Mr Aabo addressed guests invited to Hyundai Mipo Dockyard on 15 August, that figure had risen to 57,000 hours and this second generation of the engine has benefited from that operational experience, he said.

Kjeld
Kjeld Aabo, Dir, new technologies, MAN Energy Solutions

Improvements include simplified fuel delivery arrangements, such as connecting the methanol supply via one block at cylinder cover No 1 on the six-cylinder engine. Another important change affects how the fuel line connects to the fuel booster injection valves (FBIVs), which are vital components to the engine’s functioning.

Each cylinder has two FBIVs for the methanol and two standard fuel vales to deliver diesel – as a pilot fuel when operating in dual-fuel mode or for full engine power when methanol is not being used – and in this latest design, the connections are made inside the cylinder cover.

Other changes to the cylinder head have also helped to simplify its design, something that is appreciated by onboard engineers. One of them commented to ShipInsight during a tour of the first of the new-generation ships, Mari Couva, that the previous cylinder head had many small pipes; now most of those are inside the block and it is much easier to maintain, he said. In addition, “when you are walking around the cylinder head you don’t need to look out to avoid some small pipe that could break.”

The most significant change between the two generations is yet to be installed on the ships: by adding water to the fuel these engines will meet IMO Tier III NOx emission standards without the need for SCR or an EGR; more details about this planned upgrade can be found via the link, above, to our earlier item about these ships.

A considerably larger amount of fluid must be injected when operating in this mode to provide the same amount of fuel energy since water could represent up to 40% of its volume. The methanol injectors already have to cope with higher pressures than normal to inject enough fuel – because methanol has only about half the calorific value of conventional fuel – so when water is added, the injection period starts earlier and lasts longer to allow for the additional quantity.

“The [FBIVs] are over-engineered to withstand that extra 40%,” Marinvest’s director of ship management Fredrik Stubner told ShipInsight. Like most modern engines, these units have electronically-controlled fuel injection which makes it possible to make such changes automatically, he pointed out.

At present, Tier III standards only apply in the North American and US Caribbean emission control areas (ECAs) but they will also come into effect in the Baltic and North Sea ECAs on 1 January 2021.

Lubrication

Lubricating methanol-fuelled engines is a challenge since, unlike conventional fuels, methanol does not have any inherent lubricating properties. In addition, because methanol contains no sulphur, a low base-number (BN) lube oil is needed, since there is no sulphuric acid to neutralise. But it is also important to have high detergency and that “is something we are still working on,” Mr Aabo said.

Mr Stubner told ShipInsight that when the company began operating with methanol fuel, a BN25 lube oil was recommended, with BN100 used when running on HFO. But experience showed that these lubes did not offer enough detergency and he provided a copy of an MAN Energy Solutions service letter dated May 2018 that recommended using BN40 oil when running on methanol and BN140 with HFO.

Marinvest uses Chevron lubes, he said, “and since the very beginning I have ensured they are very much involved with our project and they are … analysing our data [and are] in frequent dialogue with MAN Energy Solutions as required.”

Chevron Marine Lubricants pointed ShipInsight to a White Paper it had published in 2017 – before the service letter mentioned above - and which ShipInsight mentioned shortly afterwards. The white paper notes that, post 1 January 2020, many ships will be dual-fuelled, “resulting in more extreme operating conditions within the engine.” This means that, “without proper guidance, choosing the right cylinder oil with the correct BN and feed rate can be particularly challenging.”

The paper goes on to describe the first two of Waterfront’s methanol-fuelled ships, Mari Jone and Mari Boyle, as “the product of a collaboration between several leading industry innovators” including Chevron Marine Lubricants, along with Waterfront, Methanex Corp, Marinvest and MAN Energy Solutions.