Rolls-Royce Power Systems has successfully tested what it claims is the world’s first high-speed marine engine powered exclusively by methanol, at a specially redesigned test bench in Friedrichshafen, Germany. This project was undertaken through the meOHmare research initiative, funded by the German Federal Ministry for Economic Affairs and Energy, which combines the expertise of Rolls-Royce, injection system specialist Woodward L’Orange and the WTZ Roßlau technology and research centre.
Using methanol requires significant changes to engine design, including modifications to the combustion process involving the fuel system, the charging and engine control systems, as well as all engine subsystems that come into contact with the fuel. The entire fuel system is made of stainless steel, to prevent corrosion.
The first test hours are said to have shown that the engine runs well, with only fine-tuning now required. “We are currently improving the settings so that the engine runs smoothly and accelerates cleanly under load,” says Dr. Johannes Kech, head of methanol engine development. By the end of 2025, all engine components will have been extensively tested and further developed, and discussions are underway with partners and funding agencies to bring the technology to practical application.
Unlike diesel, liquid alcohol does not ignite spontaneously and requires a completely new injection technology. Steffen Theiß, development engineer and project lead for MeOHmare at Rolls-Royce Power Systems, says: “The biggest challenges in designing the methanol engine are injection, mixture formation, the ignition system and the safety concept for liquid low-flashpoint fuels.” As there are no off-the-shelf methanol injectors available for this performance class, Rolls-Royce engineers are developing hardware that is durable and consistently precise in its metering.
Another challenge is to achieve a homogeneous fuel-air mixture in the combustion chamber that can burn cleanly. Theiß explains: “Due to methanol’s lower lubricity, the fuel cannot be injected into the combustion chamber at pressures of 2,000bar and above, as is the case with diesel. However, the lower the pressure, the more difficult it is to create a homogeneous mixture in the combustion chamber. The finest possible methanol droplets must be present throughout the combustion chamber so that they evaporate quickly, ensuring a homogeneous and ignitable mixture at the spark plug.”
Combustion and flame propagation are highly dependent on the mixture distribution and the charge movement in the combustion chamber. Theiß says: “The challenge with ignition is to ensure that, at the thermodynamically optimal ignition point, the mixture composition and the degree of turbulence of the flow directly at the spark plug enable ignition. Compared to a diesel engine, the charge movement in the combustion chamber must be adjusted much more precisely.”
Another aspect of the engine design is the ignition phase itself. “Since the ignition behaviour, mixture distribution and charge movement vary slightly from one combustion cycle to the next, there are also significant fluctuations in combustion and consequently in the pressure build-up in the cylinder and the power output,” says Theiß. “In comparison, diesel engine injection and combustion are much more reproducible, so that the combustion cycles differ only slightly from one another.”
Rolls-Royce developed the safety concept of the new engine type in accordance with DNV requirements. Theiß says: “Unlike diesel engines, ensuring the necessary safety levels requires a double wall with ventilation. We paid particular attention to having a compact installation space and in addition we have integrated systems for detecting methanol.” The team developed a new safety concept specifically for the test bench. This included special flame detectors, methanol detectors, ventilation systems and a flushing concept for all lines.
The combustion process for the methanol engine has been tailored to work with a specially designed turbocharging system, to ensure clean combustion, rapid boost pressure build-up and high efficiency across the entire operating range. The result is that the engine combines the dynamic response of high-speed diesel engines with a fuel that advances the maritime energy transition. “For operators, this means familiar performance and a better carbon footprint,” concludes Theiß.
While the methanol engine concept is generally suitable for all marine applications, the company is initially focusing on workboats, tugs, ferries, offshore support vessels and yachts. The next stage will be to identify a pilot ship to test the new engine under operational conditions at sea.
