Dual fuel Maritime Energy Systems: Speed models and analysis

The shipping industry’s transition towards cleaner fuels would entail an increase in the cost and complexity as the number of potential fuels increases coupled with other parameters such as fuel availability, future price uncertainty and policy measures that could possibly impact each choice differently. Alongside any major changes be it new policies or adopting new fuels are new challenges to maintain efficient shipping operations as shipping companies may need to more frequently re-evaluate over time investments and/or tactical decisions concerning ships that can utilize alternative fuels when the relative fuel prices diverges or as the supply chain for alternative and/or synthetic fuels develops.
The transition towards full decarbonization in the maritime industry would require a change in the current fuel mix away from fuel oil as the main fuel for marine propulsion. When considering which alternative fuel to adopt, the energy content of the fuel as well as the cost of implementing the required systems on board can be huge. The volume and weight of storage required will influence the operating range of the vessel throughout its lifespan which is typically 20 years. Dual fuel engines for example have the ability to run in three distinct modes: fuel-oil-only mode, gas modes (minimum pilot oil) and mix dual fuel mode. These modes can be switch seamlessly even during operations and allows the ship operators greater flexibility in choosing which type of fuel to utilize, analogous to having a physical option throughout the lifetime of the vessel. Such flexibilities may be particularly beneficial whereby it may even be optimal to have a fleet of ships with several fuel mixes.

Academic literature regarding the flexibility to utilize a mix of both fuels with dual fuel marine engines is limited which necessitates a study on dual fuel vessels in its own right. This report presents the results of a preliminary study in a dual fuel-liquefied natural gas context concerning flexible bunkering, speed models in a flexible fuel setting and a flexible fuel mix with constraints on fleet level carbon emissions. In this context, the transition towards a multi-fuel maritime sector necessitates a study to analyze the economics of some of these alternatives as several alternative propulsion systems and energy efficient technologies with different working principles, technological lifespans such as electric barges, fuel cells, fixed sails etc., as well as alternative bunker fuels i.e. liquefied natural gas, methanol, grid power etc. for ships become more readily available amidst multiple pathways of compliance in the industry’s transit towards a multi-fuel future in order to decarbonize and meet the environmental agenda.

The research work in this thesis consists of two major parts. Firstly, to extend academic literature on bunkering for liner shipping with the application of dual fuel engines in providing fuel flexibility subjected to limited liquefied natural gas bunkering facilities. New liquefied natural gas bunkering facilities have developed in recent years along a subset of the major shipping lanes East of Suez. This is critical to the uptake of LNG as a bunker fuel while with the installation of dual fuel engines, vessels operators will now have a choice regarding the main fuel for propulsion. An additional layer regarding the combinatorial aspect of different fuel types to utilize as well choice to bunker at LNG facilities enroute (not calling port) is incorporated subjected to maintaining weekly schedules by speed adjustments.

Secondly, to analyze speed optimization and speed reduction models for liner shipping in a flexible dual fuel LNG context with regards to the current ongoing speed limit debate at the IMO. The focus is on the interplay of an average speed limit on the optimal speeds, carbon intensity and emissions in conjunction with fleet deployment. For a perspective, the case where carbon neutral drop in fuels can be utilized in variable proportions but at high prices in order to maintain sailing at higher speeds as an alternative to speed reductions subject to the same environmental constraint if the fleet were to reduce speeds is examined as well.
Carbon-neutral fuels are a necessary pre-requisite for a fully decarbonize shipping industry, although fuel flexibility with dual fuel engines can facilitate that transition in the short to medium term as the supply chain for carbon-neutral fuels develop by allowing a flexible fuel mix intermittently.