The Naval Architect: January 2018
The Energy Efficiency Design Index (EEDI) established a baseline for CO2 emissions from vessels in terms of grams of CO2 per tonne (of cargo) per nautical mile. The EEDI is being phased in gradually. By the time Phase 3 kicks in from 2025 onwards, the requirement is a reduction of 30% against baseline.
So now the shipping industry has emission reduction targets, how will it achieve them? Can this, as the main marine engine builders suggest, be achieved with the advances made in new engine, turbocharger and propeller designs? Are coating suppliers also able to contribute? Do we simply switch fuel?
Most of the two-stroke engines now being installed are long stroke engines with a higher power to weight ratio, which increases propulsion efficiency. To improve the efficiency of an engine manufacturers will seek to improve the ratio of the maximum pressure i.e. the firing pressure and the mean effective pressure. The greater the ratiom, the higher the engine efficiency is and the lower the Specific Fuel Oil Consumption (SFOC).
MAN Diesel & Turbo says “With the constraints given by the engine design itself b – mainly how high the maximum acceptable pressure inside the cylinder is (the most important parameter) when designing engine structures, bearings, combustion chamber components. and how high the maximum acceptable power (crankshaft design) is – the efficiency of a modern two-stroke main engine and a modern four-stroke auxiliary engine is in fact close to the maximum theoretical efficiency. The efficiency of both engine types is approx. 50%, and further improvement will require significant design efforts, especially when ever-tighter emission legislation has to be fulfilled.”
But further improvements can be made says MAN Diesel & Turbo: “Since we are very close to what is theoretically possible for high-performing two- and four-stroke engines, the efficiency gain has been limited to 1-2% for the two-stroke engine and somewhat more for the four-stroke engine. However, it is important to note that with the ultra-long-stroke G-type engine design, directly-driven larger-diameter propellers can be fitted to ships and, thereby, form the basis for a significant improvement of the overall ship propulsion efficiency. For certain ship types, this improvement of the propulsion efficiency combined with an improved ship design has resulted in up to 20-25% reductions of CO2 emissions per tonne-mile.”
Significant advances have been made with the four-stroke engine too. According to Patrik Wägar, Product Director, Medium Bore Engines at Wärtsilä Marine Solutions: “With the market introduction of our latest engine type the Wärtsilä 31, the Guinness World record for four-stroke engines was broken reaching efficiency over 50% on the output shaft.”
“The Wärtsilä 31 incorporates technologies such as electronic fuel injection, 2-stage turbo-charging, hydraulic valve actuation, a new generation Control and Automation System the UNIC 2 and a more robust base design to withstand higher pressures and increase thermal loading.”
Wägar furthers “Looking back, we have improved efficiency by approximately 1% every three and a half years, so 10% over 35 years. With the Wärtsilä 31 a big leap was achieved with efficiency improvement of 1.5 – 4% units depending on fuel type and load range. With the release of a new platform, the potential is built in for upgrades and further efficiency improvement. The limits have been pushed forward. During the next 5-20 years we will see several design upgrades both in terms of improved efficiency, increased output and reduced emissions.”
In all types of engine there are efficiency gains to be made mechanically. By improving the lubrication and the materials of all engine parts subjected to friction further improvements in the overall efficiency of the engine can be made. The predominant area for frictional losses is the piston ring package. Therefore, manufacturers have put a great deal of effort into reducing this loss.
Bearings are another source of friction and again material and lubrication improvements contribute to a reduction in losses and therefore improved efficiency.
Another way that has been proven to improve efficiency is the switch from mechanical control of engines using camshafts to electronic control. Electronic controllers can monitor and adjust for more parameters during the operation of the engine.
Electronically controlled turbocharging also has a part to play in improving a ships overall efficiency. By having a system that adjusts to the operating condition of the engine manufacturers have been able to reduce the SFOC by up to 3%.
Efficiency gain: 5-8%
Waste Heat Recovery
As the in-engine gains are becoming smaller further improvements are being found elsewhere within the ships systems. MAN Diesel & Turbo says: “Although small, we do expect that we will continue to see improvements in engine efficiency. However, the big gains in CO2 emissions reduction are expected to come from improved synergies between the engine and a waste heat recovery system, from intelligent utilisation of hybrid solutions (potentially batteries).” The engine builder continues: “In combination with a waste heat recovery system, the efficiency of the prime mover will increase to approximately 60% from the approximately 50% today for a standalone engine.”
Efficiency gain: 10%
Computer Aided Design
Wärtsilä’s Wägar, meanwhile, adds that the new developments in computer assisted engineering techniques can help to improve the overall efficiency of the engine. “Through simulations and virtual validation techniques we get a good view of the potential in theory, and today simulations have been improved that much that we are surprisingly close to what we see in reality. We do not want to revweal numbers at this stage, but there is clear potential. We are confident to keep a pace of 1% improvement every 3.5 years, perhaps even escalate the progress.”
Efficiency gain: 2-5%
Another way of improving a ships efficiency is the hull coating. Over at Hempel they have been developing Hempaguard. Hempel claim “Hempaguard can deliver six per cent fuel savings across the entire docking interval compared with best-in-class antifouling solutions. Since its inception in 2013, Hempaguard has been very well received by ship owners and operators around the world with over 800 full vessel applications. This is thanks to its unique technology – the patented Actiguard technology.”
“The only hull coating to combine the low surface friction of silicone with efficient fouling preventing biocides in a single coat, Hempaguard achieves outstanding resistance to fouling, even during idle periods of up to 120 days. Hempaguard goes one step further in delivering efficient operations as it retains its effectiveness when switching between slow and normal steaming offering unrivalled flexibility in fleet utilisation.
“Hempel also recently launched a new antifouling coating range, the Globic 9500 series. These are two premium antifouling coatings – Globic 9500M and Globic 9500S – which offer customers a potential 2.5 percent reduction in speed loss, equating to significant fuel savings and lower CO2 emissions. This significantly improves the operational efficiency of a vessel and minimises the operator’s environmental footprint.
“This new range of antifoulings have been specifically designed for new buildings and dry-dockings. Globic 9500M (M for maintenance) protects against slime as well as soft and hard fouling. Globic 9500S (S for static) protects against hard fouling even during extended outfitting periods.
“Interestingly these two coatings are built on nano acrylate technology that provides full and immediate antifouling protection the moment the vessel is placed in the water. It encompasses a fine polishing control mechanism to bring the integral biocides to the surface at a steady and stable rate.”
“Together these two coatings deliver unparalleled protection and are the next step in high performing antifouling protection offering customers improved operational efficiency, flexibility and a high return on investment.
Hempel continued: “We also believe in offering the right services to further assist our customers achieve operational efficiency. For example, we have a hull performance management team that works with customers to accurately measure performance data of the hull. This determines the environmental efficiency and performance of the vessel, and subsequently the return on investment of the hull coating. Utilising this information correctly and determining exactly how fuel savings are being achieved, we can offer solutions and discuss making adjustments if the performance of the vessel drops.”
Efficiency gain: 6%
A great deal has been made about Liquefied Natural Gas (LNG) being the panacea for ships’ fuel. However, the fact that LNG is predominantly methane which is a greenhouse gas (GHG) 28 times more potent than CO2 is usually ignored. Methane slip through the entire supply chain not to mention through the engine has the potential to negate any benefits LNG may offer. There are better alternative fuels such as methanol which do not have the hazards associated with LNG.
Efficiency gain: 0-20%
So, as a very simplistic analysis the possible accumulated gains are 23-29% improved efficiency before we consider a switch of fuel. Both MAN Diesel & Turbo and Wärtsilä Marine Solutions are continuing to develop engines with greater efficiency. By combining these engines with other technologies, such as waste heat recovery to generate electricity, and advanced coating technology, the future emissions targets appear achievable.