GEEN RAY study credits engine technology advancements for lower methane emissions

The GREEN RAY project has published its findings on methane emissions from a study carried out onboard the Wasaline ferry Aurora Botnia which is powered by LNG.

The study was conducted by a team of experts from the VTT Technical Research Centre of Finland, comprising Kati Lehtoranta, Niina Kuittinen, Hannu Vesala, and Päivi Koponen.

The research focused on emissions from the exhaust of two Wärtsilä 31DF engines onboard the vessel. Operating on its normal route between Vaasa, Finland, and Umeå, Sweden, the engines were studied under five different load conditions.

Notably, one of the engines implemented a new combustion concept, running on liquefied natural gas (LNG), while the other employed a standard setup built in 2021.

The study’s results revealed that the methane emissions from the Aurora Botnia were lower than those reported in previous onboard studies featuring similar-sized low-pressure dual-fuel engines. While the new combustion concept led to a slight increase in CO2 emissions, the overall CO2 equivalent, considering both methane and CO2, was smaller than that of the standard dual-fuel engine. This finding underscores the significant potential of recent advancements in engine technology to benefit the environment by reducing emissions.

Additionally, the new combustion concept engine exhibited lower levels of nitrogen oxides (NOx) and formaldehyde compared to the standard dual-fuel engine. However, it was observed that particle emissions increased in comparison. These findings present an important consideration for further development and deployment of methane slip abatement technologies, the study said.

Decarbonizing maritime transport stands as one of the most significant challenges facing the shipping industry. LNG, with its composition primarily consisting of methane, has emerged as the leading alternative fuel in the transition towards renewable and low-carbon options. When combusted in a low-pressure dual-fuel engine, LNG emits considerably less CO2 compared to traditional fuels like diesel. It also generates negligible amounts of particle emissions, nitrogen oxides (NOx), and sulfur, meeting the stringent Tier III limits set by the International Maritime Organization (IMO).

However, LNG as a marine fuel has been on the receiving end of a lot of criticism due to the occurrence of the methane slip, which is the unintentional release of methane during the storage, transfer, and combustion processes. Although LNG engines are designed to minimize methane emissions, there is still a possibility of leakage or incomplete combustion, leading to methane being released into the atmosphere.

Furthermore, while LNG emits lower levels of CO2 and other pollutants compared to traditional marine fuels, critics argue that the overall greenhouse gas emissions associated with LNG may be higher when considering the full life cycle of the fuel. The process of extracting, liquefying, and transporting LNG involves energy-intensive processes, which can contribute to indirect emissions and environmental impact.

That being said, there is no exact data on the impact of methane slip on the overall emissions of a vessel as the quantification of methane slips has been rather sporadic and the information on the matter has been limited.

This is one of the reasons industry majors joined hands under the GREEN RAY project.

The project is coordinated by VTT Technical Research Centre of Finland, and it brings together shipyard Chantiers de l’Atlantique, ship owner CMA CGM, classification society DNV, the Finnish Meteorological Institute, ship manager MSC Cruises Management, non-profit organisation Revolve Water, energy major Shell and technology group Wärtsilä. Most recently it was joined by seven new members.