Because internal combustion engines have been designed to run on hydrocarbon fuels, any decarbonisation initiatives require fuels with a lower or zero carbon content leaving just hydrogen to provide the energy for the engine to run.
As the most common element on the planet, hydrogen would seem an ideal choice, not least because when combusted in air the only by product would be water vapour. Pure hydrogen can be used in an engine and no doubt will be included in the future marine fuels mix but it presents three particular problems.
Its energy density at ambient temperature, its characteristic of making metals brittle and its ability to diffuse through many materials including metals. Hydrogen can be liquidised to increase the energy density in the same way as LNG, but to remain liquid hydrogen has to be stored at temperatures below -253°C.
However, hydrogen in its pure form is not found on earth and is only available as a chemical compound combined with other elements. Hydrogen must either be extracted from the compound or the compound itself must be combustible.
The most common hydrogen containing compound is water (H20) but that is not suitable for use as a fuel for internal combustion engines. Ammonia (NH3) can be burned and looks at the moment to be a promising carbon-free fuel for the mid to long term.
Marine engine manufactures see the internal combustion engine as an excellent choice to utilise hydrogen, but energy can also be obtained by combining hydrogen with oxygen in a fuel cell to produce electrical energy, heat and water.
Exploring all avenues
Wärtsilä has had feet in both camps pursuing both engine and fuel cell technology through the 21st Century. In 2010 the Finnish technology company installed a 20kW solid oxide fuel cell on board the car carrier Undine owned by Wallenius Marine. Despite planning to develop fuel cells for ships in a number of collaborations, Wärtsilä decided in 2013 to withdraw from the sector. This year Wärtsilä became involved in a new fuel cell project underway in Norway and involving tanker operator Odfjell, fuel cell specialist Prototech and Lundin, an offshore oil & gas company.
Although fuel cell technology was put on hold, Wärtsilä was still researching the potential of hydrogen but now as a fuel for internal combustion engines. In 2015, tests were carried out using LNG as a fuel enriched with up to 25% hydrogen and found to be promising. Research has continued using higher quantities of hydrogen and also pure hydrogen. It is hoped to have an engine running on pure hydrogen at some point in the very near future.
Kaj Portin General Manager, Sustainable Fuels, Wärtsilä’s Marine Power believes that although hydrogen will have a place in the marine fuel mix, there are problems to overcome and it may not be suitable for all vessel types. For ships that need a long sailing range, the space needed to store the fuel is the biggest hurdle. Although storage in a liquified state is possible this requires extreme low temperature or alternatively very high pressure at ambient temperature.
Hurdles to clear
For ferries and other vessels with a short endurance requirement, hydrogen is more feasible assuming the shore infrastructure for regular bunkering is in place. A big problem for any ship will be periods of low or no activity such as when waiting at berths or anchorage. In a refrigerated tank, the hydrogen will begin to boil off in the same way that LNG does in an LNG carrier and must then either be vented or reliquefied which would require additional machinery.
Portin believes that demand will likely be far stronger from power production than from marine. Partly this is due to the space requirement for storage being far less of an issue for a power station than for a ship. Another reason is that the production of hydrogen can take place closer to the point of use removing the issue of transporting the fuel.
He also says that regardless of the final user, the hydrogen used needs to be green and not produced in a less sustainable way. Currently around 95% of all hydrogen production is what is termed ‘brown’ hydrogen with the gas being extracted from fossil fuels including coal. Although using brown hydrogen as a fuel would reduce pollution at the point of use, overall it actually involves even more emissions that using fuel oil in a ship.
Another issue that needs to be overcome for ships using hydrogen as a fuel is the twin matters of hydrogen embrittlement and diffusion. Many of the materials used in marine diesel engines are not ideal for use with hydrogen as a fuel allowing both problems to take place. Portin says that these matters are currently being researched and investigated by Wärtsilä’s metallurgy specialists.
Much of the research around hydrogen as a marine fuel is being funded and promoted by regulatory bodies such as the EU and this may well lead to solutions being found for the various issues identified and yet to be discovered. Some believe that for hydrogen to be considered as a marine fuel there may need to be subsidies available to offset the likely additional cost of the fuel and also for building the infrastructure needed for storage and bunkering.