The first MAN Energy Solutions’ two-stroke, low-pressure, Otto-cycle engines will contribute to making LNG carriers more efficient
Four years ago, SK Audace became the first LNG carrier fitted with two-stroke, low-pressure, dual-fuel X-DF engines from Swiss-based Winterthur Gas & Diesel (WinGD). Since that initial success, LNG carrier owners have gravitated to the two-stroke, Otto-cycle X-DF engines for their operating efficiency and environmental advantages – ‘out-of-the-box’ compliance with IMO Tier III, low NOx emissions, and virtual elimination of sulphur oxides and particulate matter.
Moreover, shipowners weren’t complaining about the lower capex offered by the engines, which do not require certain additional ancillary equipment associated with Diesel-cycle, high-pressure DF engines. This stems from the relative high cost of the fuel gas supply system (FGSS), including the high-pressure compressor, for boosting the pressure of the BOG to the 300-bar injection pressure needed for the ME-GI – an investment only needed for LNG carrier applications.
With LNG shipowners clamoring for Otto-cycle, low-pressure engines, Copenhagen-based engine designer MAN Energy Solutions set out in late 2017 to design its own version to fill a gap in its portfolio. The result of that research is the ME-GA engine, unveiled in a live stream event by the Danish engine designer’s Copenhagen Research Centre in March.
When announcing the first orders for the ME-GA in July, MAN Energy Solutions senior vice president and head of two-stroke business Bjarne Foldager said: “The ME-GA’s genesis owes much to us recognising a strong market desire for a lower-cost alternative to the ME-GI engine, driven primarily by the LNG carrier market”.
“These ships will be 35% more efficient than required by EEDI”
Mr Foldager said the engines would “deliver lower methane-slip compared to existing, Otto-cycle LNG engines, and better fuel-efficiency in both gas and fuel-oil modes” when coupled with the company’s exhaust gas recirculation (EGR) system. “This further confirms our leadership in the critical, dual-fuel, marine segment,” he said.
Using an EGR reduces NOx-emissions, ensuring IMO Tier III- compliance in diesel mode for the ME-GA. MAN Energy Solutions reports that EGR will enable the ME-GA to reduce specific gas consumption by about 3%, and specific fuel-oil consumption by 5%. Expectations are that the EGR will slash methane slip by 30 to 50% and improve the stability of the Otto-cycle combustion process, in which fuel and air are premixed and burned at a relatively high air-to-fuel ratio.
Integrated into the engine design to minimise the engine’s footprint, the ME-GA EGR solution interacts with the exhaust gas before the turbocharger. Its design-similarity to that of ME-C engines’ EGR systems will lower its price point, since the supply chain and components are already matured, said MAN Energy Solutions.
Additionally, the volume requirements of the ME-GA EGR system are also significantly lower, requiring less pipework than low-pressure EGR solutions.
First orders for ME-GA
South Korea’s Hyundai Heavy Industries Engine Machinery Division (HHI-EMD) has placed orders for 12 MAN B&W 5G70ME-GA10.5 engines, two of which will be fitted in each of six 174,000-m3 LNG carriers.
Two of the LNG carriers are being built for KLC, two for PanOcean, one for Knutsen LNG and one for JP Morgan Asset Management.
Delivery of the first engine by HHI-EMD is set for August 2022, with the final unit arriving at the shipyard in 2023. All of the engines will be fitted with MAN Energy Solutions EGR systems.
The six LNG carriers will be built by HHI and sister company Hyundai Samho Heavy Industries for charter to Shell Tankers (Singapore) Pte Limited on delivery. These newbuildings are part of at least 24 that Shell has secured on long-term charters to transport LNG from its portfolio as of mid-July.
When it comes to minimising each vessel’s carbon footprint and maximising its energy efficiency, the new ME-GA engines will not be the only advanced technology on board. “These ships will be 35% more efficient than required by the energy efficiency design index (EEDI) and 20% more than required by the annual efficiency ratio, delivering significant emissions reductions for our time-charter fleet,” said Shell global head of shipping and maritime Grahaeme Henderson.
As part of Shell’s time-charter fleet, each ship’s performance will be optimised by analysing real-time data from the ships and deploying Shell’s proprietary draft and trim optimisation software Just Add Water System (JAWS), to enable further efficiencies and emissions reductions.
Developed in co-operation with the University of Southampton, the software uses historic, high-frequency data from the vessel to determine the optimal conditions on previous voyages, which enables the system to advise on how best to enhance a vessel’s draught and trim at any given speed to reduce fuel consumption and lower emissions. JAWS monitors and reports live fuel and emissions savings back to managers, to give real-time feedback.
Floating on air
Other features designed to improve the LNG carriers’ EEDI are air-lubrication systems and shaft generators for auxiliary power, along with optimised hull forms and design speeds. Air lubrication systems (ALS) produce a thin layer of microbubbles along the full flat bottom of the vessel, reducing frictional resistance between the water and the hull, lowering fuel consumption and emissions in the process.
Shell is looking to fit air lubrication systems not only on newbuilds, but existing ships, too. More than a year ago, it inked a three-year framework agreement to retrofit an unspecified number of LNG carriers with air lubrication systems from UK-based Silverstream Technologies. Based on in-operation trials, Silverstream Technologies said its system reduces fuel consumption and associated greenhouse gas (GHG) emissions by between 5-10%, depending on the vessel’s operational profile.
The 2010-built, Shell-chartered Methane Patricia Camilla was fitted with a Silverstream ALS during its planned dry docking at Sembcorp Marine Admiralty Shipyard in October 2020.
Following operational testing of the retrofitted technology, Silverstream and Shell engineers demonstrated 6.6% net savings generated by the Silverstream system. The technology was tested at various vessel speeds during Methane Patricia Camila’s normal operations to calculate fuel and emissions savings.
South Korea’s Daewoo Shipbuilding & Marine Engineering (DSME) has developed a number of energy -saving devices for newbuildings and retrofits to support EEDI and Energy Efficiency Existing Ship Index (EEXI) compliance. Besides its own ALS, DSME has developed duct, pre-swirl stators, rudder bulbs and long caps to improve fuel efficiency by controlling the flow around the hull, the DS bow to reduce wave-making resistance, hybrid propulsion using shaft generators and batteries, and rotor sails to harness wind power.
Meanwhile, MAN Energy Solutions continues to build its portfolio of two-stroke, dual-fuel engines for a multi-fuel future. The 158 DF engines in operation have accumulated over 1.7M operating hours burning alternative fuels such as LNG, LPG, ethane and methanol. It expects to introduce a dual-fuel engine capable of operating on ammonia by 2024.
“If the fuel is commercially interesting to the industry, then … we will develop the best solution for the industry for that,” said Mr Foldager.
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