The ‘green marine’ fuel quest 16 May 2023

shipping greenhouse gas emissions

Maritime shipping has long been dominated by heavy diesel engines, which contribute to global warming. Could that all be about to change as punitive new regulations come into force, asks Brian Wall

Global shipping spews out 3% of worldwide greenhouse gases [GHG], reports the European Union – or more than 144 million tonnes of CO₂ in 2019. “With the maritime industry responsible for transporting no less than 90% of world commerce, there is increasing pressure on the sector to reduce its carbon footprint swiftly,” it states.

It’s a situation that is of much concern to Syed-Asif Ansar, head of department, energy system integration, at the German Aerospace Center Institute of Engineering Thermodynamics. “While 3% might not seem titanic in scale, growth in demand for shipping worldwide means that maritime emissions have been accelerating faster than most other sectors,” he says. “Without action, shipping could be responsible for 10-13% of global emissions within a few decades. To curb its carbon emissions and reduce its pollutants, the shipping industry needs to accelerate technology progress on new power generators such as fuel cells and on synthetic fuels based on renewable power.”

It seems appropriate, therefore, that maritime shipping is being included in the EU emissions trading scheme (ETS) that starts in 2024. How will this work and in what ways might it affect maritime engineering?

First, the salient details. Amendments to the International Convention for the Prevention of Pollution from Ships (MARPOL) Annex VI entered into force on 1 November 2022. Developed under the framework of the Initial IMO Strategy on Reduction of GHG Emissions from Ships, agreed in 2018, these technical and operational amendments require ships to improve their energy efficiency in the short term and thereby reduce their greenhouse gas emissions.

From 1 January 2023, it became mandatory for all ships to calculate their attained energy efficiency existing ship index (EEXI) to measure their energy efficiency and to initiate the collection of data for the reporting of their annual operational carbon intensity indicator (CII) and CII rating.

According to International Maritime Organisation (IMO) secretary-general Kitack Lim, “The short-term GHG reduction measures, adopted in 2021, form a comprehensive set of amendments to MARPOL Annex VI, which provide important building blocks for IMO’s future mid-term greenhouse gas reduction measures.” Adds Lim: “Decarbonising international shipping is a priority issue for IMO and we are all committed to acting together in revising our strategy and enhancing our ambition.”

IMO member states are actively engaged in the process of revising the Initial IMO Strategy on Reduction of GHG Emissions from Ships, with a view to adoption of a revised strategy in mid-2023. For the maritime sector, regulators are allowing a phase-in period. This has the advantage that only a share of the overall emissions will need to be compensated during the initial years, with the first submission of certificates (EUAs) to EU authorities beginning in April 2025.


Bernhard Schulte Shipmanagement (BSM) is one company developing a range of solutions to support its customers to navigate the complexity of the upcoming requirements. “BSM has been focusing on the EU Emissions Trading System for some time, because it will have extensive impact on our and our clients’ business,” says Sebastian von Hardenberg, chief financial officer of BSM. “We invest in the development of specialist teams and IT tools required to ensure a smooth EU ETS process and certificate administration for owners and their charterers. As ship managers, we will offer transparent live data-driven applications, showing a vessel’s consumption in relation to geolocation and time, as well as the resulting EU ETS exposure.”

As set out in the EU ETS regulations, ship owners and operators will need to acquire emission permits for 40% of their applicable emissions in 2024, increasing to 70% in 2025, and 100% in 2026 and every year thereafter. This is applicable to intra-EU voyages and voyages between EU ports and non-EU ports. The costs incurred depend not only on emitted emissions, but also on volatile EUA prices. “Low-emission fleets, combined with efficient digital performance solutions and an intelligent trading strategy for EUA certificates, will therefore be crucial on future competitiveness,” adds von Hardenberg.

The responsibility to pay for EUA certificates first lies with the charterer, then the ship owner, as per the ‘polluter pays’ principle. However, in the eyes of the EU regulator, the statutory responsibility for non-compliance lies with the DOC (document of compliance) holder.

“As a DOC holder, this will expand the exposure and tasks of a ship manager,” says von Hardenberg. “At the same time, it will strengthen our role as part of the maritime industry – if we are able to offer strong solutions to master these complex requirements.”


A group of academic and industrial partners is embarked on a £5.5million grant-funded project to accelerate the understanding, technologies and policies relating to the use of ammonia as a sustainable marine fuel. The lead investigator is Prof Alasdair Cairns, chair in propulsion systems, engineering faculty, the University of Nottingham, where the majority of the research is being undertaken.

“As countries seek opportunities for decarbonisation, there is a great deal of interest in green ammonia as an energy vector and a fuel for commercial shipping,” he says. “However, there are a number of considerations relating to the greenhouse gas emissions of international shipping. Roughly 80% of the emissions from the maritime sector are emitted by larger commercial vessels, where alternative solutions such as electric and fuel cell remain limited in energy density and/or cost. This challenge is compounded by the fact that the engines in these vessels typically remain in service for several decades.

“Ammonia represents an attractive solution,” adds Cairns, “but significant challenges remain around slow combustion and the emissions of NOx, and it is these challenges we wish to address through research in fast-burning and ultra-low NOx combustion systems.”


Practical research relevant to this project is underway at the university’s Powertrain Research Centre in the faculty. This is focused on a new Volvo marine specification compression ignition (diesel) engine, jet ignition engine and suite of Signal Group exhaust gas analysers. Liquid ammonia is stored in a tank at the centre where research fellow Abdelrahman Hegab (pictured below) and research technician Nigel Sykes have installed a fuel supply line to the Volvo engine, which draws vapourised ammonia from the tank.

However, the combustion characteristics of ammonia differ greatly from conventional fuels, so the researchers are looking at ways to refine the technology, while maximising the efficiency with which energy is utilised and minimising potentially harmful emissions.

“The burning velocity of ammonia is relatively low,” states Hegab, “so there is potential for unburned ammonia to pass through to the engine exhaust. For this reason, Signal Group has supplied us with their new S4 NEBULA, a continuous ammonia analyser which employs tunable diode laser spectrometry (TDLS). This analyser is deployed in conjunction with a comprehensive suite of Signal’s reference method analysers to ensure that we are able to gain a full understanding of engine emissions under differing research conditions.”

Brian Wall

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Bernhard Schulte Shipmanagement (Isle of Man) Ltd

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