Decarbonisation Technology February 2026 Issue

the need to gain experience in handling these alternative fuels in a safe way, considering the toxicity of ammonia and the risks it poses for seafarers, harbour personnel, and the public at large. All of this suggests it may be prudent not to count on a very rapid scale-up of new ZNZ fuel technology to meet the NZF base targets. Regulatory considerations Going into the regulatory detail on how exactly to encourage the use of ZNZ and transitional fuels is beyond the scope of this article. Looking at the NZF as proposed, there is a lot of attention on the GFI reduction trajectory. However, the global average GFI attained will be the result of thousands of individual decisions made by shipowners and ship operators, as well as fuel manufacturers and suppliers. Their decisions will be driven primarily by confidence in a business case for alternative fuels. From a shipowner/operator perspective, this means that it should be more economic to operate a ship on an alternative fuel than continuing to use conventional fuels. In the case of using surplus units (SU) as defined in the NZF, this can be expressed in a simple equation as a necessary condition to create a solid business case: Price of alternative fuel – compensation received for SUs – depreciation factor < price of conventional fuel + cost of SUs needed whereby the depreciation factor represents the write-off cost for the additional vessel cost to enable the use of the alternative fuel, expressed in $ per ton of fuel consumed. Perhaps the delay in the adoption of the NZF offers an opportunity to reflect on what is needed to create a sound business case for both ZNZ and transitional fuels. This analysis shows the value of transitional fuels in moving towards the longer-term NZF objectives, but also in providing real near-term emissions reductions from shipping, giving more time to build experience and capacity for the longer- term solutions.

perspective. Changes in fuel specifications are made in a cautious way to make sure that an improvement in one aspect does not lead to unintended consequences elsewhere. As an example, when introducing the 0.50% sulphur requirement in 2020, concerns arose around the stability of low-sulphur fuel blends, leading to extensive work to develop guidelines and update ISO fuel standards to avoid on-board problems with unstable fuels. Introductions of new technologies, such as ammonia-fuelled vessels, typically follow an S-curve, with the development of know-how in the initial years, followed by a strong increase once the technology is fully demonstrated on a commercial scale. The uptake of LNG as a marine fuel is a case in point. Hence, scenarios with a strong role for transitional fuels make sense: they help bridge the period during which ZNZ fuels will go through their initial period of experience and know-how building, allowing a faster ramp-up towards the ultimate 2050 IMO net-zero target. Another example: LNG was introduced as a marine fuel to achieve large reductions in emissions of SO2, NOx, and particulate matter, but it soon became apparent that, depending on engine type and engine load, some methane can escape through the funnel. This is undesirable as methane is a short-lived climate forcer with a Global Warming Potential relative to CO2 (GWP100) of 28. Engine manufacturers have since managed to develop advanced engine technology that reduces methane slip to very low levels. In this way, the advantages in air emissions from using LNG can be retained, while Tank-to-Wake (TtW) GHG emissions from two-stroke slow speed engines can be 20% to 30% lower than when using fuel oil ( Schuller, 2021 ). Combined with proper control of methane during natural gas production and distribution, this can lead to a substantial overall WtW GHG footprint reduction. Similar experiences can be expected with new ZNZ fuels. For example, when running a ship on ammonia, emissions of NOx and in particular N2O (GWP100 of 265) will need to be carefully controlled. If hydrogen is used, hydrogen (GWP100 of 12) losses will need to be minimised throughout the production and use chain. Perhaps even more important is

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Eddy Van Bouwel evbouwel@skynet.be