Advanced future fuels

In both the marine and large stationary gas engine markets, sustainability and decarbonisation goals are prompting investment in the use of greener low and zero-carbon fuels. These include advanced biofuels, methanol, ammonia and hydrogen, with each at different states of commercial readiness. When widely available, the move to these fuels would clearly be one of the most effective ways to cut carbon emissions. However, each fuel type has a number of challenges associated with its use.

Biofuels

One fuel type that could be dropped into the existing marine fuel pool is biofuel. Fatty acid methyl ester (FAME) or hydrotreated vegetable oil (HVO) have well-established bio-credentials. And now a number of biofuels including those created by recycling used cooking oils and forest product residues are being tested in ocean-going ships. The marine world will be watching to see if there are any adverse effects on the equipment and the fuel processing on board these vessels. If not, these fuels may be widely accepted in marine applications since the fuel, which can be used without engine modification, delivers a reduction in carbon dioxide emissions and ‘virtually eliminates’ sulphur oxide (SOx) emissions. However, availability and cost are issues here and it is likely that on-road transportation will create a strong pull on scarce supply.

Ship trials have shown that biodiesel can also contribute towards a reduction in total hydrocarbons, particulates and carbon monoxide. However, oxides of nitrogen (NOx) emissions are generally higher. Lowering the peak combustion temperature and using combustion improver technology are effective ways to help reduce the NOx contribution from biofuels that are incorporated into the marine pool.

Marine biofuels introduce different lubricant performance requirements with regards to oxidative stability and cold flow properties.

Supply constraints aside, we can expect an increased use of bio-blends as a viable option to contribute towards greenhouse gas (GHG) reduction while we wait for other alternative fuels come online.

Methanol

In the marine sector, methanol has a number of advantages – it has low SOx, NOx and particulate matter emissions, is biodegradable and widely available. However, on the downside it can be expensive, has a low energy content compared to other fuels and has a flash point of only 12^oC.

In 2020, IMO approved methanol in its interim guidelines for low-flashpoint fuels.

This has led to increased interest in it as a suitable compliant fuel today and to help carry internal combustion engines into future technology platforms. The use of methanol in marine engines will introduce very different lubricant performance needs, and it is likely that additional corrosion inhibitors and antioxidants, will be required and care will be needed with respect to both the detergent itself and any destabilisation of the detergent core.

Ammonia and hydrogen

The advantages of ammonia are that it is a carbon-free fuel that can be burnt in a combustion engine using a pilot fuel or used to power fuel cells. However, as well as being toxic and corrosive, ammonia has a lower energy density and is heavier than heavy fuel oil (HFO) and needs to be stored at very low temperatures or at a pressure of 10 bar. Despite these challenges, ammonia is already being evaluated by a number of OEMs as a fuel to help shipping cut GHG emissions. Since, from an emissions standpoint, it is a much lower carbon route to take, we are likely to see the experience being gained with ammonia in marine ventures passed on to the power generation side.

As for hydrogen, on the plus side it is a zero-emissions fuel that can be burnt in a combustion engine or used to power fuel cells. But just as with the other future fuels it has its downsides in that it must be stored at high pressures or low temperatures and its high flammability and highly reactive nature give rise to safety concerns. In addition, current high costs and lack of available infrastructure are also barriers to its adoption. More effort is needed to scale up production and to replace high-carbon hydrogen produced from coal and oil with low-carbon green hydrogen made by using clean electricity from surplus renewable energy sources, such as solar or wind power, to electrolyse water. Despite its current drawbacks, the environmental and sustainability credentials means there is a high appetite for investment here and a number of OEMs are already evaluating its use.

One of the key issues with the use of hydrogen and ammonia is how to burn them in a spark ignited gas engine. 

The issue with hydrogen is that being very easy to burn it is more difficult for OEMs to control the speed of combustion. Whilst with ammonia the opposite is true in that it is not very easy to burn and takes more energy to get going. Marine OEMs are adopting a dual fuel strategy, where a diesel pilot fuel provides the ignition source to burn the rest of the fuel in the mix. Here lubricants will typically be designed to be suitable for use with the diesel fuel that is used. Alternatively a direct spark ignited gas engine, which removes the need for a separate pilot fuel, can be used, which could require new and carefully formulated bespoke lubricants.

Multi-fuel future

It looks fairly certain that the future lower/zero carbon and more sustainable fuel mix will be even more diverse than today. It will be important for OEMs to ensure their engines and aftertreatment systems are compatible with the new fuels. This need for compatibility will also extend up and down the supply chain – in the vessel, the bunkering facilities, storage, supply and production. In addition, it is likely that in some applications new bespoke lubricants will be needed to ensure sufficient performance and protection are delivered.

Sustainability and CO₂ emissions reduction will continue to drive innovation throughout the marine and gas engine industries.

As engine designs and fuels evolve, they will present new challenges. Infineum is working to ensure its fuel and lubricant additive technologies are matched to the new requirements that are emerging.

Download this article