The times are indeed a-changing for the conventional two-stroke engine, which is being developed into an environmentally-friendly power unit for post-2020 use, writes Selwyn Parker
With the 2020 emissions deadline hanging over the industry like an ominous (albeit clean) black cloud, engine manufacturers are unveiling increasingly advanced and ingenious solutions to make their power units cleaner and greener before it is too late.
ABB for example, now offers a direct current-based power energy management system (PEMS) designed specifically for new and alternative energy sources. The direct-current technology will be widely adopted in two- and four-stroke engines alike because PEMS facilitates rock-bottom fuel consumption with minimum wear and tear. Unlike standard alternative-current systems, direct current allows the generators to run at variable speeds.
“This [system] contrasts with traditional alternative-current systems, where generators run at a fixed maximum speed irrespective of the power demand on board,” explained ABB global product manager for onboard DC grid in the marine and ports division John Olav Lindtjorn. “This leads to excessive engine wear and poor fuel efficiency at lower loads,” added.
Not to be outdone, MAN Energy Solutions has started delivering the first of its latest emissions-reducing technology for two-stroke engines, a high-pressure system built around honeycombs.
Officially described as a selective catalytic reduction (SCR) system, the technology was unveiled in Japan early last year for sale in early 2018. Available for two-strokes of all bore sizes, it cuts back NOx emissions to IMO Tier 111 limits. Originally developed for four-strokes, the system has been reduced dramatically in size for the smaller power unit.
According to MAN’s vice-president and head of engine design Gunnar Stiesch, the technology works by providing more bang per buck. “The reactor design has been driven by the desire to reduce the SCR system’s overall size while still maintaining the effectiveness of a much larger design,” he explained. The cornerstones of its development were the honeycomb and the reactor concept.
MAN predicts “remarkable cost reductions” from the technology, which covers engines up to 25 MW. These savings would come in the form of the much simpler and faster Scheme B engine-approval process. Already well established in four-stroke engines, the Scheme B process eliminates several steps in certification because the engine is run on a test bed in a way that meets the IMO Tier 111 mode.
The MAN SCR-CP (CP standing for controllable pitch), as it has been christened, puts another NOx reduction technology on the shelf for two-strokes, sitting neatly alongside MAN’s system for exhaust gas recirculation (EGR). Unlike the SCR, which cleans emissions up after the combustion process, EGR does so by controlling them from inside the engine during combustion.
Elsewhere, two offshore-loading shuttle tankers will be launched in 2019 with a full suite of ABB’s specialist marine technology. As well as deploying PEMS, these Statoil-contracted, two-stroke 125,000 dwt vessels, currently under construction at Samsung Heavy Industries, will also feature a power distribution system called the Onboard DC Grid; this can be configured for new energy sources, such as fuel cells.
The performance of the shuttle tankers’ twin engines will be monitored by ABB’s remote diagnostic system. ABB claims handsome savings from the system, saying it “will reduce by up to 70% the number of on-call visits by service engineers and [reduce] maintenance costs by up to 50%”.
ABB said it is a firm believer in highly configurable, DC-based two-strokes. “These tankers will be future-proofed for technology and regulations for years to come,” pointed out ABB managing director for marine and ports Juha Koskela when the shuttle tankers contract was announced in March. With a working life of at least 30 years ahead of them in the North Sea, these vessels have been designed with the notion of energy transition in mind.
“It is clear that the next generation of ships – electrical, digital and connected – spells a bright future for DC-based electric propulsion,” said Mr. Lindtjorn. As he explained in a recent technical paper titled Onboard DC Grid – a system platform at the heart of Shipping 4.0, the virtue of DC-based power systems lies in their simplicity, flexibility and functional integration of all energy sources, including variable speed gensets, shaft generators, batteries and fuel cells.
“A DC and power-electronics-based power system provides a unique platform for digital solutions onboard a vessel,” Mr. Lindtjorn said. “Equipped with sensors and communication infrastructure, data is transmitted between systems in an instant.” In short, the digital age is overtaking engine technology across the global marine fleet.
ABB’s own direct-current solution – the DC Grid – is being installed in a wide variety of vessels, such as the HH Ferries-owned Aurora and Tycho Brahe which were recently converted from alternative-current systems. DC Grid is also entering service on offshore support vessels, icebreakers, shuttle tankers and, imminently, expedition vessels.
The PEMS system is shaping up to be an integral component of future-proofed two-strokes. The technology not only manages the balance of power, which is the traditional job of PEMS, it also controls the energy in the power system. As Mr Lindtjorn noted: “The latter becomes important when adding sources like batteries or super capacitators, with very finite amounts of energy available.”
In the USA, where the price of global maritime pollution is estimated at US$330Bn, conventional engines may soon be a thing of the past. Next year, passengers will step aboard America’s first hydrogen fuel cell-powered ferry.
In late June, the Californian government handed a US$3M grant to a group called the Golden Gate Zero Emission Marine to build the Water-Go-Round, an Incat Crowther-designed, 21 m aluminium catamaran that will be powered by two 300 kW electric motors using independent electric drive trains manufactured by BAE systems. Still experimental, the Water-Go-Round is due to start service in 2019.
Meanwhile, heavyweight research is being conducted on fuel cell-driven power systems. In June, Canada’s Ballard Power Systems and ABB signed an agreement to develop the next generation of fuel cells in a joint endeavour to help the marine industry clean up its emissions.
As the companies explained in a release, current fuel-cell technologies are only on a kW scale; their goal is to “pioneer MW-scale solutions suitable for powering larger ships”. They are aiming for a 3 MW capacity, equal to 4,000 horsepower, but no bigger in physical size than a conventional marine engine.
This is not wishful thinking; Ballard Power Systems has already built MW-scale, containerised systems for land-based use. Passenger ships will be the first recipients of these marine versions and since fuel-cell power is combustion-free, they will more than meet the requirements of the post-sulphur age.
Biography: John Olav Lindtjorn
John Olav Lindtjorn specialises in energy efficiency, including energy storage, at ABB. He first joined the group in 2006 and was one of the team that developed the Onboard DC Grid. Holding a Master of Science in electrical and electronics engineering from the Norwegian University of Science and Technology, he has an important role in ABB’s research and development projects.