Gas measurement needs for clean maritime fuels

As part of the 2023 IMO Strategy on Reduction of GHG Emissions from Ships, the IMO has recently announced changes that will transform maritime fuels. By 2030 the Carbon Intensity of international shipping is targeted to decline by at least 40% compared to 2008 levels.
The intent is not to eliminate Carbon from maritime fuels, nor to prohibit the use of hydrocarbons. But the carbon intensity must be considered in the life cycle analysis of the fuel. For example, burning bio-diesel emits CO2 but does not emit fresh fossil CO2 to the atmosphere. Instead, it puts CO2 back into the atmosphere that a plant has previously removed.

Safe use of Ammonia

Ammonia is a carbon-free fuel which can support the IMO carbon intensity reduction ambitions. However, it is toxic and maritime engines to burn ammonia are not widely commercially available. The risk associated with toxicity can be mitigated through the use of reliable gas detection equipment.
Ammonia gas detection will also help to prevent explosive atmospheres building up. However, if  an ammonia leak does take place and is ignited, a specialised ammonia flame detection system can be used. Ammonia is not IR-active and burns with an ‘inorganic’ flame. This means that specialised flame detectors are required.

Ammonia engine development

When using ammonia as a fuel, its combustion properties must be considered during engine design. It burns with a slow, or lazy flame and has a very high ignition energy. Ammonia-fired engines are being developed which inject a small amount of diesel into the piston in addition to the ammonia. In each piston cycle, initially the diesel is ignited and this provides enough ignition energy to burn the ammonia.
The balance of diesel to ammonia in the fuel mix is approximately 5:95, so despite there being some CO2 emissions, ammonia offers the potential for significant greenhouse gas emissions reduction in the maritime sector.
Furthermore, ammonia contains nitrogen. So, in addition to nitrogen being introduced into the combustion chamber from the air intake, it is present in the fuel itself. This presents a challenge to minimise the emissions of oxides of nitrogen which are pollutant gases.
If the combustion is in an oxygen-lean environment, for example due to poor air/fuel mixing in the piston chamber, nitrous oxide can be formed. This is an extremely potent greenhouse gas, with an impact more than 200 times as severe as CO2 per kg of gas released to the atmosphere.
From a metrological perspective, the measurement of nitrogen oxides in the emissions footprint from ammonia engines is key. Within the engine this requires rapid response sensors to enact changes to the air fuel mixture. After the engine and the exhaust gas management system traces of the pollutant gases must be measured to ensure the emissions are adequately clean.

Methanol to the fore

Methanol-ready ship orders have been on the increase since 2020. Methanol burns in a similar way to diesel meaning that engines can easily be built to accommodate both fuels. Storage of liquid methanol on board can be achieved in the same tanks that are used for heavy fuel oil. So, building a ‘methanol-read’ ship adds only marginal cost.
Methanol ready ships can operate with traditional fossil fuels today and transition to a lower carbon fuel when the bunkering infrastructure is more developed and the economics are more favourable.
As part of the fuel transition, the emissions monitoring systems must either be changed, or built to be methanol ready from day-1. For example, methanol combustion is lean in particulate emissions but can result in methanol slip or formaldehyde production. The implication is that the gas metrology and instrumentation requirements will also transition.
An additional gas-measurement challenge is within the engine itself. Sensors are used to feed data to the engine management system. A common control loop is to measure the amount of partially combusted molecules to fine-tune the fuel air ratio. In the case of heavy fuel oil measuring CO would be appropriate. In the case of methanol as a fuel, methanol slip or formaldehyde may be a more appropriate control variable for the fuel/air ratio.
Methanol contains carbon and yields CO2 when burned in the ship’s engine. However, it can be built from biogenic carbon in which case the emissions are CO2-neutral.

EURAMET Maritime metrology project

Ajoy Ramalingam, a Research Scientist at the PTB in Germany is the Project Coordinator for the MaritimeMET initiative that is funded by the European Partnership on Metrology and co-financed from the European Union’s Horizon Europe Research and Innovation Programme and by the Participating States. “MaritimeMET covers Metrology for green maritime shipping: Emission control through traceable measurements and machine learning approaches”, he confirms.
“Our work focuses on the future metrological needs of ‘Power to X’ fuels such as ammonia and methanol. We believe these fuels will play an increasingly important role in shipping and we therefore want to ensure that the gas metrology and other physical property measurement capabilities are ready to support the energy transition.”
Beyond the PTB, other participants include metrological institutes, universities, gas analyser and sensor OEMs, engine developers and shipping operators. Additionally, the consortium is collaborating with sensor manufacturers on Machine Learning model uncertainties and intercomparison studies on dynamic pressure sensor calibrations.

Connect to learn more

On the  3rd of June 2025 from 10am to 11am CEST (Central European Summer Time) the MaritimeMET project team will be hosting a webinar looking into ammonia and methanol as emerging clean fuels and the gas metrology challenges associate with their introduction.
“We are delighted that Mr Stephen B. Harrison of sbh4 consulting will make a presentation and take an extended Q&A session for this webinar,” says Ramalingam. “And, of course, we are looking forward to welcoming participants from a diverse range of stakeholders. See you there!”

Registration for the webinar is free of charge. Please see here.