Additional flexibility when supply chains vary.
Combustion behaviour, material compatibility and injection logic.
Greater procurement flexibility and a gradual transition path.
Blends must not be misunderstood as a shortcut.
Ethanol (C₂H₅OH) and methanol (CH₃OH) are both alcohols, but their physical-chemical properties differ significantly in operationally relevant ways. Methanol has a calorific value of approximately 19.9 MJ/kg; ethanol sits at around 26.8 MJ/kg. A blend of both theoretically offers a higher volumetric energy content than pure methanol, which could partially mitigate the range problem.
However, combustion chemistry is not as linear as the calorific values suggest. Ethanol-methanol blends alter the ignition behaviour, flame propagation speed and emissions profile. In dual-fuel two-stroke engines optimised for pure methanol, adding ethanol can shift the injection parameters. The injection quantity must be adjusted because the energy content per unit volume changes. Ignition delay may vary, requiring compensation from the engine control system.
On the materials side, the challenges are subtler but no less important. Methanol is known for its aggressiveness towards certain elastomers and sealing materials. Ethanol behaves similarly but attacks different materials to varying degrees. With blends, the risks do not simply add up – they can overlap in unexpected ways. Fuel lines, O-rings, pump seals and tank coatings must be tested and approved for the specific blend composition.
A particularly critical point is water uptake. Both methanol and ethanol are hygroscopic – they attract water from the environment. Blends of both substances can exhibit phase separation at certain temperatures and humidity conditions, where a water-rich phase separates from the fuel. In a bunker tank, this can lead to corrosion, filter blockage and injection problems.
Engine manufacturers are correspondingly cautious about approving blends. MAN Energy Solutions and WinGD have specified their ME-LGIM and X-DF-M platforms for pure methanol. Approval for ethanol-methanol blends would require extensive test programmes – including long-term endurance tests evaluating the effects on injector nozzles, cylinder liners and piston rings under real operating conditions.
From a procurement perspective, blends could offer a pragmatic advantage. Bioethanol is significantly cheaper and available in larger quantities in some regions – particularly Brazil and the United States – than green methanol. Blending could therefore reduce fuel costs whilst simultaneously improving supply security.
However, this concept faces regulatory hurdles. The FuelEU Maritime regulation and the EU ETS assess fuels by their well-to-wake CO₂ equivalent. The crediting of a blend depends on whether both components are certified as sustainable – and whether the mixture is treated as a standalone fuel or as a combination of two separate fuels. IMO regulations are even less clear in this regard.
For bunkering logistics, blends add complexity. The mixture must either be delivered pre-blended or mixed on site at the port. Both have consequences: pre-blended fuels require their own supply chain with quality control for the specific composition. Port-side blending requires additional infrastructure, metering and monitoring technology and clear responsibilities.
Documented operational experience with ethanol-methanol blends in maritime use remains scarce. Most findings originate from the automotive sector and stationary plants where such mixtures have been used for longer. However, transferability to large marine engines is limited, as operating conditions – high load gradients, extended continuous running times, salt-laden atmosphere – are fundamentally different.
Some engine manufacturers have conducted internal tests with blend variants but have not published the results. The reluctance suggests that the findings do not justify straightforward approval. For operators, this means: anyone considering blends must be aware that they would be operating outside the OEM specification – with all consequences for warranty, insurance and classification.
Operators should evaluate ethanol-methanol blends against the following criteria:
OEM approval: Is there explicit approval from the engine manufacturer for the intended blend composition? Without such approval, warranty claims typically become void.
Class acceptance: Has the responsible classification society accommodated the use of the blend within the existing notation? If not, a special procedure may be required.
Supply chain reliability: Can the specific blend composition be reliably procured along the entire trading route?
Regulatory crediting: Is the blend recognised as emissions-reducing by the relevant regulations (FuelEU, EU ETS, IMO)?
Any operator seriously considering an ethanol-methanol blend, rather than simply monitoring the topic, should treat it as a formal trial program and not an operational shortcut. That starts with written sign-off from the engine manufacturer for the specific blend ratio under consideration, obtained before any fuel is loaded, because retroactive approval requests after an incident carry far less weight and rarely arrive in time to matter.
A trial should run on a single vessel first, with enhanced monitoring of injector condition, cylinder liner wear and fuel line integrity at intervals shorter than the normal maintenance schedule, so that material compatibility issues surface before they cause unplanned downtime. Fuel samples from every delivery should be tested for water content and phase stability, since the hygroscopic behaviour of both alcohols means that a supply chain reliable for pure methanol is not automatically reliable for the blend.
The classification society and hull and machinery insurer should be informed before the trial begins, not after a claim arises. Operating outside the OEM specification without informing these parties can jeopardise cover regardless of how carefully the trial itself is managed, and a documented, pre-approved trial protocol is the only basis on which warranty and insurance questions can be resolved cleanly if something does go wrong during the test period.
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