Recent developments among Japanese and Chinese four-stroke engine suppliers will offer more options for operators looking to use LNG as a marine fuel
LNG has been used in four-stroke engines for more than a decade now, but there are still advances to be made. One such development priority involves reducing pilot fuel oil consumption and expanding the gas fuels that can be used. Recent projects in China and Japan highlight the approach to these challenges.
A pure gas, four-stroke engine developed in China is ready to be put into service, according to enginebuilder and designer Shanghai Marine Diesel Engine Research Institute (SMDERI).
The company’s eight-cylinder M23G engine deploys the lean-burn, Otto cycle method of low-pressure gas injection. It is notable for its ignition process, initiated by a spark plug in a pre-combustion chamber that features a separate gas supply to the engine cylinder. The air-to-fuel ratio in the cylinder is controlled by a throttle which adjusts the air inlet and exhaust wastegate.
The M23G meets IMO Tier III NOx emission limits without after-treatment. The eight-cylinder version, with a bore of 230 mm and a stroke of 320 mm, boasts a power output of 1,600 kW at 1,000 rpm.
The engine, which has been in development since 2015, has accumulated 600 hours on the testbed, while a prototype based on SMDERI’s 6CS21 diesel engine has been installed on a tugboat and has been operated for several hundred hours. China Classification Society has issued a type approval certificate for the new engine.
"SMDERI's lean-burn engine is notable for its ignition process, initiated by a spark plug in a pre-combustion chamber that features a separate gas supply to the engine cylinder"
“The design, production and test phase are complete and the engine has already been well developed,” says Li Xiang of SMDERI’s new technology department. “Based on the successful application of the 6CS21 diesel engine, we believe that the M23G will be accepted by the market in the near future.”
SMDERI’s gas engine development programme follows the introduction of the CS21 medium-speed diesel engine range in 2011. The company also co-designed the Auxpac 16 generating set with Wärtsilä. Described as the world’s smallest generating set, it delivers 735 kW through six 160 mm-bore cylinders.
While SMDERI is aiming to allow operators to run purely on gas, another engine designer is taking measures to broaden the range of gas fuels it can use. Japanese enginebuilder Daihatsu is in the final stages of validating a new technology that would enable its LNG-burning engines to use LPG as fuel.
The company’s solution involves an onboard gas reformer to convert propane-based LPG into substitute natural gas (SNG), which can be used in the company’s dual-fuel engines. The technology was presented publicly for the first time at a regional event held by internal combustion engine council CIMAC in Kobe in October 2018.
LPG is more readily available than LNG, is easier to handle and boasts a similar emissions profile. But the variability of the component gases (mainly propane and butane) makes it difficult to use in engines. Daihatsu’s solution is to follow land-based gas reforming principles: desulphurising LPG, methanising it by steam reformation and then removing carbon dioxide and water to leave SNG that can be burned in engines alongside LNG.
The company studied a traditional gas reformer plant before installing a scaled down prototype, which could eventually be put on board a ship, at its factory in Moriyama. There, Daihatsu conducted reformed gas evaluation tests using the factory’s power generator.
"LPG is more readily available than LNG, is easier to handle and boasts a similar emissions profile. But the variability of the component gases makes it difficult to use in engines"
At the same time as testing the prototype gas reformer, the company investigated the performance of reformed gas in its lean-burn, dual-fuel engines. This included identifying combustion timings and the speed at which engine load could be ramped up, finding a slightly longer combustion time than for Japan’s City Gas, but a quicker ramp-up to full engine load. A gas composition test identified the ratio at which methane and propane need to be mixed during the reforming process, dependent on engine load.
In the final stages of development, Daihatsu is now examining the long-term reliability of engines operating on reformed gas, as well as evaluating the deterioration of the reformer catalyst.
While engine developers in Asia advance LNG concepts, one of the world’s biggest manufacturers of marine four-stroke engines, Wärtsilä, is looking ahead to a gas fuel of the future - hydrogen.
Hydrogen, which burns in engines with no carbon or sulphur emissions, could soon be produced using renewable electricity, if promising advances in electrolysis are realised to a commercial scale. For this reason, countries around the world are investing in researching and developing hydrogen energy networks. For some – notably Norway – this has led to early initiatives exploring marine applications for hydrogen-powered fuel cells.
Given the need for hydrogen fuel onboard ships with fuel cells, it could make sense if engines on those ships could also burn hydrogen. With this in mind, Wärtsilä recently conducted an experiment into burning hydrogen in its dual-fuel and spark-ignited, pure gas, medium-speed engines.
Results suggest that, in tightly controlled parameters and with extra safety precautions for handling the gas, Wärtsilä’s engines could run on a mix of natural gas – or LNG – that comprises a maximum of 30% hydrogen.
If commercialised, the development would offer the chance for many gas-fuelled ships to consider hybrid power arrangements that include fuel cells, with hydrogen fuel onboard used to power fuel cells or engines.
MAN extends reach in offshore wind
Two nine-litre MAN 21/31 engines in diesel-electric configuration will drive United Wind Logistics' new deck carrier
Elsewhere, MAN Energy Solutions has added two unusual four-stroke engine-powered vessel references to its installed base in early 2019, both serving the burgeoning offshore windfarm sector.
A new heavy-lift crane installation vessel for Oslo-based Offshore Heavy Transport (OHT), the Alfa Lift, will be powered by four MAN 12V32/44CR gensets with a total output of 28,800 kW. The vessel will be built at China Merchants Heavy Industry’s shipyard in Nantong with delivery due at the end of 2020. The order includes options for three more vessels.
Alfa Lift is designed to install all types of bottom-fixed offshore wind foundations. It will also transport and install topsides and subsea modules, as well as other heavy cargoes in the oil and gas sector. It features a free deck length of 148 m and free deck area of 8,100 m² on the main deck, with a further 2,470m² on the foredeck.
The company will also supply two MAN 9L 21/31 and two MAN 6L16/24 gensets to an unusual heavy cargo deck carrier under construction at Jiangsu Zhenjiang Shipyard for Hamburg-based United Wind Logistics. Designed by engineering company HeavyLift@Sea, the vessel will transport very heavy but fragile turbine components in the North Sea and Baltic Sea.
The ship design squeezes 3,600 m² of deck space, with a loading capacity of 10,000 tonnes at maximum draught, onto a vessel that is 148.5 m long and just 28 m wide. This was achieved in part by making the superstructures, including the 21-person accommodation block, as compact as possible.
The requirement for deck space also proved challenging for the propulsion installation, especially for the positioning of the exhaust funnel and selective catalytic reduction units. A diesel-electric configuration was the chosen solution, with engines installed near the ship’s bow and a propulsion room with electric motors driving fixed-pitch propellers via conventional shafting in the aft.