What Is Seen As The Most Important Alternative Fuel To Diesel?

• Methanol is increasingly seen as the most important alternative fuel to diesel for reducing the carbon footprint of vessels using four-stroke engines.
• There is demand for tugboats, port support vessels and those providing coastal services to use high-speed methanol-combustion engines. 

A recent news article published in the Riviera states that Methanol leads the pack on four-stroke fuel alternatives.

Characteristics and challenges of alternative fuels

They discussed the characteristics and challenges of alternative fuels during Riviera Maritime Media’s Power plant and gensets: how new fuels are changing engine design webinar, held 30 August during Rivera’s Marine Propulsion & Marine Lubrication Webinar Week. 

On the panel were GasKraft Engineering owner Hinrich Mohr, MAN Energy Solutions vice president and head of research and development for four-stroke engines Alexander Knafl and Cummins director of business development and tug segment leader Eddie Brown. 

The experts considered the operational, safety and maintenance challenges of new fuels for prime movers and gensets, concluding that biofuels are viable now, methanol is likely to be adopted in the medium term and eventually ammonia will be introduced for marine fuels in the second half of this decade. 

Mr Mohr said some alternative fuels are available, or will soon be ready for two-stroke, slow-speed propulsion engines. 

Solutions for four-stroke medium- and high-speed engines

“Solutions for four-stroke medium- and high-speed engines are in different stages of maturity,” he said, “but challenged by the wide variety of alternative fuel options in combination with the engine specifics.” 

More work is needed on testing, certification and validation of alternative fuels on engines and gensets, but the technology is ready. “Most fuel technology is clear, but needs improvement and testing,” said Dr Mohr. “We need regulations from IMO and the fuel supply chain needs to be built up.” 

Alternative fuels need ignition sources such as pilot fuels and fuel-supply options include direct injection or port-fuel infection. Vessel owners will need reliable solutions for newbuildings and retrofits, that are low maintenance and need minimal extra crew training. 

Fuel properties come with challenges including increasing system complexity, sophisticated engine controls and integration with batteries, motors and other power sources in one propulsion system. 

Owners will question which is the right fuel for their application; what the engine concept will look like, how the fuels influence capital and operational expenditure; and are they fit for the vessel’s purpose? 

“Based on the wide variety of alternative fuels, a multi-fuel engine concept would be preferred, but realisation is challenging due to the different fuel properties,” said Dr Mohr. 

Ammonia testing and HVO 

Mr Knafl said MAN is testing an ammonia-fuelled engine in Copenhagen, Denmark, and is developing methanol combustion engines for marine applications. 

“Ammonia on high-speed engines is the most challenging. If we start with high-speed engines, we can unlock those challenges,” said Mr Knafl. 

“But methanol is an option for the entire marine segment and works well on tugs with four-stroke engines on vessels working locally or on specific routes. Methanol is being adopted for tugs, ferries, container ships and over a broad range of applications.” 

Mr Knafl said a short-term solution is using hydrogenated vegetable oil (HVO) in four-stroke engines to reduce the well-to-wake carbon footprint for owners. 

“HVO is a champagne fuel. It is great as a diesel alternative and has been thoroughly tested on smaller engines,” he said. Vessel owners can then mix in alternative fuels for field testing. 

But to reach 2040 and 2050 goals on cutting out greenhouse gas emissions, owners will need to adopt environmental e-fuels such as e-hydrogen, ammonia, and e-methanol, which show the greatest potential. 

These fuels are likely to be introduced into combustion engines through one of three methods – high-pressure direct injection of the diesel cycle, or low-pressure, port fuel injection or low-pressure direct injection of the Otto cycle. 

Methanol platform 

Mr Brown agreed HVO will be used in the short term and then methanol in the longer term. 

“HVO is approved for several platforms and a range of products. We have started this journey and have approved HVO on some engines, while still working on others.” He expects HVO to be approved for most engines in 2023. 

Mr Brown said methanol will be effective on tugs, workboats and other port and offshore service vessels. “It helps solve the green problem,” he said. “Methanol’s energy density is not as good as diesel but is better than hydrogen and ammonia, and it does not need high-pressure storage tanks.” 

However, sourcing methanol from renewable sources can be challenging. 

For zero-carbon emissions, even green methanol would be a challenge, which is why there is interest in developing ammonia and hydrogen as fuels for commercial ships. 

“Ammonia is challenging for smaller vessels such as tugs as it does not ignite well and is corrosive,” said Mr Brown.  

“Hydrogen is most challenging for its low energy density and storage issues.” Vessels using hydrogen will need large high-pressure tanks and changes in their operations to enable more frequent refuelling. 

“Hydrogen and ammonia will need new protocols for storage and handling, but methanol has less challenges,” said Mr Brown. 

“There still needs more work on validation and certification. It is viable, scalable and uptake will be significant.” Mr Brown said the maritime industry needs to identify the best green variants on local, regional and international levels, while “harmonised regulations are needed to drive focus and reality sooner rather than later.”