Diesel cycle simplifies dual-fuel methanol 2-stroke design

There’s good reasons why WinGD has chosen Diesel cycle combustion for its dual-fuel 2-stroke methanol engines: “Combustion is fully based on the conventional diesel engine design, so it’s essentially a diesel engine with an additional injection system for methanol,” says Marcel Ott, Head of Strategic Marketing.

This means that both fuels can be burnt at the highest possible efficiencies to provide the same power output and full redundancy of the diesel engine remains available. Additionally, the SCR catalyst selection and sizing requirements to meet Tier III are the same, because NOx emissions are greater for diesel fuel than for methanol.

The methanol injection system is lean by design and features a spring controlled injection valve, low pressure sealing barrier with air ventilation and an integrated purge valve that is hydraulically actuated. The system’s operation involves:

• Actuation oil supply unit pressurises oil up to 300 bar in the actuation oil rail
• Actuation oil flows to each methanol booster unit (MBU) (1x cylinder)
• Low pressure (13 bar) methanol flows on upper part of MBUs
• Solenoid (Rail) Valve activates oil ingress in the actuation control unit of the MBU
• Piston and plunger within the MBU boost methanol pressure up to 600bar
• High pressure methanol is pushed in the injection pipes and lifts injection valve needles: methanol injection occurs.

Pilot fuel injection is required to stabilise the combustion timing, as methanol has a relatively long ignition delay. At high load, less than 5% of the energy requirement is met by the pilot fuel. Towards low loads, the relative share of pilot fuel increases. WinGD’s testing has demonstrated that running on methanol brings 2% higher fuel economy than diesel. It’s possible to achieve higher efficiencies running on methanol because the specific fuel oil consumption versus NOx emissions trade-off that is made for diesel fuels is more favourable with methanol. “Diesel cycle engines are usually tuned in a way that makes them NOX compliant, but not by much because you want to squeeze out the maximum efficiency. That means the performance of diesel engines is typically limited by NOx emissions, and with methanol as a fuel there is a better trade-off between NOx and consumption.”

The 2% reduction in fuel consumption was verified on a 10-cylinder, 92-bore 10X92DF‑M engine which was run on a testbed at CSSC-MES Diesel (CMD) in Shanghai in mid-December. The engine is installed on the fourth of a series of 16,000 TEU container vessels being built for COSCO Shipping Lines at COSCO Shipping Heavy Industry (Yangzhou) shipyard. The new engines provide 52000kW x 75rpm, weigh 1,953 tonnes and have overall dimensions of: 21.5m x 11.4m x 16.9m.

The single-fuel diesel 10X92-B engines installed on the three earlier vessels in the series have since been converted for methanol with the first vessel showing great success in recent sea trials.

Using the conventional diesel engine design will simplify the conversion – the methanol injection system, including new cylinder cover, is the only new equipment that will need to be added. The combustion chamber design and cylinder design remain the same between the two engine types. “Even compression ratios remain the same,” says Ott.

An upgrade to engine control software will be required. “We have one common software platform among all engines that can handle all fuel types. So, the hardware is already there, and from a control perspective, it’s only an update of the software that is required.”

Testing has also been performed on a 52-bore test engine, and this bore size would normally have been the first to be commissioned on a vessel, but with COSCO’s incoming order, WinGD built a one-cylinder 92 bore test engine to finalise its research and development and validate the technology on the same bore size prior to deployment on the first customer project.

Other orders for the X-DF-M include 82, 62, and 52-bore engines for bulkers, tankers, container ships, and car carriers. Owners include COSCO Shipping Lines, COSCO Shipping Bulk, COSCO Shipping Energy, Maersk, ONE, Seaspan, and Evergreen.

WinGD is working on diesel-to-methanol conversion packages that are expected to be available this year. “We’re ready to discuss projects,” says Ott, who cites the comment of one customer after a demonstration: “Introducing a new fuel like methanol will inevitably add complexity to the engine, but my impressions from the 10X92DF-M was that you have found some good and – very important for the engine crews – service friendly ways of handling this complexity by good design and engineering work.”