Decarbonisation Technology - November 2023 Issue

by BAR Technologies (see Figure 1 ). Each sail is predicted to save 1.5 tonnes of fuel per day at sea.  Engine optimisation . Medium-speed four- stroke internal combustion engines used either as main or auxiliary engines are already reaching 50% efficiency, but further improvements are still to be had. Special attention should be paid to combustion efficiency in low-pressure gas- fuelled engines, as an increase in combustion efficiency directly translates into lower methane emissions. An example of technology development to reduce methane emissions and increase engine efficiency was recently demonstrated on board the Aurora Botnia RoPax ferry as part of the SeaTech project (see Figure 2 ). Aurora Botnia is a state-of-the- Figure 1 Pyxis Ocean bulk carrier fitted with two rigid wing sails to reduce fuel consumption ( ©CHEK project/Cargill )

art ferry powered by four Wärtsilä 31DF dual fuel gas engines as part of a hybrid propulsion system. One of the installed engines was upgraded to reach sizeable emission reductions and ultra-high energy conversion efficiency by precisely controlling the fuel mixture at every operating point of the engine. The VTT Technical Research Centre of Finland conducted a measurement campaign on board to verify the results. Measurements were conducted on the upgraded engine and one of the non-modified Wärtsilä 31DF engines. Figure 3 illustrates the main results on measured methane emissions from both the non-modified engine (Main Engine #4, or ME4) and modified engine (Main Engine #3 or ME3) (Lehtoranta, Kuittinen, Vesala, & Koponen, 2023). The achieved emission reduction is quite clear and sizeable, ranging from a 50% reduction at the highest loads to up to 75% at lower loads.  Engine and fuel optimisation . Having gone through the first four optimisation steps, the remaining gap for the required emission level will have to be tackled by optimising the carbon intensity of the fuel burned on board. Where the preceding steps often result in increased vessel profitability, this last step will increase the operational cost of the vessel. However, this is about to change. With legislation under development that includes so-called ‘market- based measures’ – such as carbon taxes, fuel levies or subsidies on renewable fuels – the playing field starts to tilt towards the utilisation of renewable fuels. With this in mind, Wärtsilä is developing a portfolio of engines able to run on methanol, ammonia, and hydrogen. Working to a compressed timeline, the market Figure 2 M/S Aurora Botnia photographed in the Vasa archipelago

14.0

ME3, GC ME4, GC ME3, FTIR ME4, FTIR

12.0

10.0

8.0

6.0

4.0

2.0

100

Engine load (%)

Figure 3 Methane emissions measured on board Aurora Botnia for Main Engine 4 (non-modified W31DF) and Main Engine 3 (equipped with the technology developed in the SeaTech project) ©Lehtoranta, Kuittinen, Vesala, & Koponen