Preparing shipping’s prime movers for hybrid power

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“Two-stroke engines will drive big ships for the foreseeable future – but the main engine may become smaller.” Speaking at the ShipInsight Conference earlier this year, WinGD Global Sales Director, Volkmar Galke, offered one view on future propulsion trends. As shipping aims to reduce emissions, engines will be supplemented by other power sources, meaning the engine itself may have a reduced footprint while the overall propulsion system delivers the same power output. This is just one implication of shipping’s hybrid revolution.

The demand is clear. While carbon-neutral fuels are needed to help shipping meet its 2050 target of halving total greenhouse gas emissions, these fuels will not be widely available before another important deadline. By 2030, IMO aims to have cut shipping’s carbon intensity (or emissions per transport work) by 40%, based on the 2008 levels. WinGD’s X-DF engines have already greatly reduced the emissions levels through their benchmark low-pressure dual-fuel technology, but to reach the future IMO targets, energy efficiency measures are also needed. The increasing use of electrical energy – potentially using batteries to store energy surplus efficiently produced by onboard sources like rotor sails or solar panels – is one way of cutting emissions.

Using others power sources alongside engines requires several considerations beyond installed engine power. Among the most important is how energy will be managed. At any one time should propulsion be powered by the engine, the batteries, the alternative sources directly or by a combination? Managing these energy flows can be complex, explains Stefan Goranov, Program Portfolio Manager – Digital & Hybrid at WinGD.

“With just an engine driving the propeller, there is a relatively clear relationship between ship speed, engine power output and fuel consumption. With multiple power sources this is no longer the case.”

Hybridisation is already widespread on smaller vessels powered by four-stroke engines, but its adoption on larger vessels using two-stroke engines is more challenging. One reason is the wide variety of system configurations, determined by the objectives set for particular applications.

“To maximise efficiency there must be a match between the system topology and managing the energy flow,” explains Mr Goranov. “The selection of components in terms of power rating, capacity, physical size and weight is crucial. Oversizing leads to inefficiencies, but undersizing might lead to safety issues.”

Provided that the system components and the energy management strategies are appropriately selected, hybrid systems have great potential to improve the energy efficiency of ships with two-stroke engines. WinGD is prepared for this trend. The Winterthur-based developer of low-speed engines is developing an integrated hybrid propulsion system complemented with an enhanced engine diagnostics and a new energy management system.

In the development of the new hybrid solution, WinGD has analysed several different combinations of hybrid technologies on multiple vessel types. One key finding is that hybrid technologies when deployed alongside LNG-fuelled X-DF engines can further reduce GHG emissions by around 5% (on top of significant energy efficiency gains from X-DF engines), dependent on efficiency characteristics, battery capacity and main engine rating. A large portion of this gain is achieved by using hybrid power sources to reduce fuel consumption of the auxiliary engines.

Further gains are possible by integrating solar panels, for example. But the energy they would produce is only a small portion of the demand. A theoretical calculation shows that even covering a very large crude carrier with solar panels could generate only around a third of the power produced by the vessel’s main engine. Such options are further limited by a rather high initial investment, outweighing any savings from using less fuel or rationalizing the installed power on board. Indeed, Goranov reiterates that even more realistic emissions reductions can be easily negated if the hybrid arrangement is not optimised for the specific vessel and application.

An important element of managing a hybrid system is improved engine control and diagnostics. New WinGD integrated control electronics (WiCE) control architecture was launched in June 2019 and is now being rolled out to the new engine portfolio. It includes vastly upgraded connectivity to account for current and future demands for effectively integrating the engine with ever more ship systems for overall system performance enhancement.

Alongside the new control architecture, diagnostics system WiDE (WinGD integrated digital expert) also lays the groundwork for future digitalisation around ship power and propulsion. The first version, introduced in 2018, uses model and statistical-based methods to benchmark engine performance against set milestones such as factory tests and sea trials. In latest versions, the company offers artificial intelligence-based (AI) methods to find insights that are not otherwise detected and incorporates them to the diagnostics. The next generation of WiDE will expand beyond the engine, providing real-time advice on optimising overall system operation.

“It is not feasible to generate one model of the complete energy system,” says Mr Goranov. “It is just too complex. Instead you need to deploy algorithms for each sub-system and use what is known as a hybrid approach – a combination of model-based and data-driven methods– to generate insights about how to maximise the overall system performance.”

This is exactly the approach taken in a current WinGD collaboration with the Swiss Federal Institute of Technology (ETH) in Zurich, to enhance WiDE with AI (artificial intelligence)-based features for prognostics. This will allow WiDE to provide plausible advance indication of anomalies and performance degradation. Self-assessment capability will mean that engines and propulsion systems can define the maintenance or optimisation they require, enabling real-time advice on optimising operations.

These control and diagnostic advances will both feed into the new hybrid solution when it is made available later this year. As Mr Goranov explains, whatever other power sources are applied on a vessel, the engine remains the core.

He concludes: “The full potential of a hybrid system can only be reached when all components, and in particular the main engine, are integrated efficiently. For the sake of an effective and efficient system integration, knowledge and access to the main fuel consumer – the main engine – is crucial.”