Ammonia more suited for 2-stroke engines - GCMD

Ammonia would be a better option for larger vessels than smaller ones, hinted a recent post from Global Centre for Maritime Decarbonisation (GCMD) chief executive, Lynn Loo.

PHOTO: 3D image of WinGD's dual-fuel ammonia marine engine. WinGD

Since ammonia has a high auto-ignition temperature, it ignites and burns more slowly than fossil fuels. Therefore, ammonia-powered engines need a certain amount of pilot fuel, such as diesel, for ignition and combustion. This need for a pilot fuel would potentially keep the vessels dependent on fossil fuels for a long time.

Based on an analysis conducted in August, ENGINE estimated that ammonia-powered ships could consume 5-20% of pilot fuel.

However, during her visit to Swiss engine manufacturer Winterthur Gas & Diesel’s (WinGD) engine research centre, GCMD’s Lynn Loo found that pilot fuel requirement could go as high as 30% in four-stroke engines.

“WinGD’s 2-stroke engines need < 5% pilot fuel,” she wrote in a social media post, “To the contrary, 4-stroke engines need much more pilot fuel (as high as 30%) because they run at more revolutions per power stroke.”

Four-stroke engines are ideal for powering smaller vessels including feeder vessels, ferries, fishing vessels or cruise ships, according to German engine maker MAN Energy Solutions (MAN ES). Two-stroke engines are suitable for larger vessels like tankers, large and ultra-large container vessels and bulk carriers.

The high pilot fuel consumption of smaller vessels powered by four-stroke engines would undermine the overall use of cleaner bunker fuels like ammonia. Since pilot fuels contain fossil components, these vessels would still produce substantial greenhouse gas (GHG) emissions despite using a fuel with zero-emission potential.

“So, the slow-burning character of ammonia is more compatible with the operations of a 2-stroke engine,” Loo added. WinGD will start validating its ammonia-fuelled engine concepts later this year, according to the company website. The engine maker is expected to bring its dual-fuel ammonia engines into service from the first quarter of 2025.

It is possible to replace diesel with biofuel or synthetic alternatives such as synthetic marine diesel oil (MDO) or dimethyl ether (DME) or even combine it with carbon capture technologies for ships. However, the timeline for the widespread availability of these fuels and technologies is still uncertain. 

Ammonia would therefore be ideal for fuelling larger vessels in the near future until cleaner pilot fuel options are widely available.

By Konica Bhatt

Please get in touch with comments or additional info to news@engine.online