The IMO Strategy on Reduction of GHG Emissions from Ships sets the target of net zero emissions from international shipping by 2050, including an increased uptake of future carbon-neutral fuels. Indicative checkpoints for emissions reductions are set for 2030 (a 20-30% reduction compared to 2008) and 2040 (a 70-80% reduction compared to 2008).
At the same time, the EU’s Emission Trading System (EU ETS) is also playing a part. Under this new regulation, ships sailing to or from ports in the EU and European Economic Area (EEA) must report on their emissions each year, and the biggest emitters must pay more for extra carbon allowances. The scheme covers carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) emissions, with the latter two included from 2026. The EU also has strict GHG reduction targets for 2030 and 2050, aiming to reduce emissions to at least 55% below 1990 GHG levels by 2023, and aiming for net zero emissions by 2050, in line with European Climate Law.
In order to meet those targets, the industry must accelerate the transition to future carbon-neutral fuels, especially those based on green hydrogen, including methanol and ammonia. This entails a much wider investment in the green hydrogen infrastructure to supply not only shipping, but also other hard-to-abate industries, including steel, chemical and cement production. Roughly $9 trillion is needed from now to 2050 to supply enough green hydrogen for those industries to reach net zero by 2050. Given the complex stakeholder landscape, the scaleup is expected to take many years.
Since those carbon-neutral fuels are currently both scarce and expensive, marine technology leaders are looking for ways to create a bridge through this prolonged energy transition, one that allows them to reduce emissions and keep sailing until there is enough carbon-neutral fuel for everyone. This has seen the emergence of a new kind of ship engine, the dual fuel engine.
Building a dual fuel bridge to a carbon-neutral future
As the name suggests, dual fuel engines are effectively engines that can run on two different fuels, with the ability to switch between fuels as necessary. They are designed to run on either a primary or a secondary fuel, with two different fuel injection systems – each tailormade for the specific fuel – and two different tanks of fuel. The primary fuel is generally the lowest in carbon intensity, either a future carbon-neutral fuel like methanol or ammonia, or a transitional fuel like liquefied natural gas (LNG). The secondary fuel is generally a conventional fuel that can be used when the primary fuel is not available.
This maintains business continuity and also ensures that ships do not become stranded in the middle of the ocean. Until carbon-neutral fuels are plentiful and affordable for most vessels, dual fuel engines are the most effective bridge through the energy transition.
Paolo Tremuli, Head of Turbocharger Application, Far East, and New Turbocharger Technologies at Accelleron, explains, “In principle, any fuels can be utilized in a dual fuel engine. The most common primary fuel choice has been LNG, since LNG is abundant and affordable, and reduces emissions by 25% compared to conventional fuels. However, for new build orders, methanol is rapidly catching up as a primary fuel choice, and ammonia orders are also growing. The rapidly growing orderbook for new dual fuel ships should result in a more sustainable global fleet that complies with new emission regulations and helps the industry to progress towards IMO targets.”
The use of dual fuel engines can offer vital flexibility to ship operators, given the disparity in fuel availabilities around the world. Ports in Europe, including Rotterdam, along with Los Angeles and Long Beach in the US, and Singapore in Asia, may have more carbon-neutral fuels available, for example. These ports have been investing in expanded bunkering capabilities for future fuels. Meanwhile, operators can switch back to more traditional fuels when sailing between other locations.
Overcoming the challenges of multiple fuels
“The main challenge of a dual fuel engine is to combine two different combustion systems in the same space,” Paolo explains. “Usually, combustion requirements are quite different for different fuels, and therefore they require different solutions. For dual fuel engines operating with diesel and LNG, for example, the diesel is a liquid fuel and burns according to the diesel cycle. Meanwhile, LNG is injected into the engine as a gas, and burns using the Otto cycle.
“In addition, LNG burns unevenly and is quite prone to knocking, which can cause wear or damage to the engine and other components. As such, it requires additional controls when it comes to managing the amount of air that’s present in the cylinder, to prevent irregular combustion.”
Methanol and ammonia are currently the most promising carbon-neutral fuels in shipping. These fuels can both potentially be burned as part of a dual fuel solution in a reciprocating engine, using either the diesel cycle or the otto cycle. Of course, there are important safety considerations. Since ammonia is corrosive and the fumes are toxic, it is important to prevent leakage to spaces where people are present. Ship operators need to ensure that people in the engine room wear protective equipment to avoid inhaling the ammonia fumes or getting the liquid on their skin or in their eyes. With appropriate procedural updates, ammonia-fueled vessels can be safely operated.
Dual fuel engines can also incorporate a third fuel as a blend. “It’s possible to mix a third fuel such as ammonia or hydrogen within the engine port,” Paolo explains. “While quantities of such carbon-neutral fuels are still very limited, incorporating small quantities of them into LNG can further reduce emissions.
“Currently, hydrogen is quite common as a third fuel, in ratios of up to around 20%. To include a higher percentage of hydrogen, further engine modifications would be required, such as reducing the engine compression ratio or increasing the amount of air in the cylinder. A similar approach can also be taken when it comes to ammonia. We’re likely to see these ratios increase in the future as technology evolves, leading to cleaner shipping even before we convert to carbon-neutral fuels on a wider scale.”
How Accelleron is supporting the dual fuel transition
Turbochargers have a key role to play in enabling the dual fuel strategy, starting with a 10% increase in engine efficiency. “On the one hand, you want to make expensive, limited carbon-neutral fuels go as far as possible. On the other, you want to limit the emissions from conventional fuels. The answer to both of those is to enable the highest possible combustion [energy] efficiency for a strategy that employs a range of fuels, from carbon-neutral fuels to conventional fuels. That means calibrating the air pressure according to the fuel type and engine load,” says Paolo.
Fuel injection systems are equally as important to enabling the safe and efficient use of multiple fuels in dual fuel engines. Both material and design demands are complex in dual fuel engines, and each engine requires a tailored fuel injection approach. (Read the in-depth interview on fuel injection systems for dual fuel engines and carbon-neutral fuels with Marco Coppo, CTO of Accelleron’s Officine Meccaniche Torino (OMT).)
Digitalization is another important enabler of efficiency and safety optimization for dual fuel ships and fleets. From engine performance and hull and propellor insights to voyage optimization and emissions reporting, Accelleron’s digital solutions support shipping owners and operators in devising the most efficient, flexible, and economical sustainability strategies for dual fuel fleets.
Tackling the carbon-neutral fuel infrastructure challenge
The biggest challenge remains future carbon neutral fuels themselves. Large-scale production and distribution of fuels such as methanol, ammonia and hydrogen, and staking out a priority claim for these fuels in the shipping industry – against demands from multiple hard-to-abate industries – remains the chief barrier to an accelerated energy transition. And it is one that can only be overcome in concert with many other sectors and stakeholders.
Green Shipping Corridors Around the World
“The introduction of green shipping corridors is helping to tackle the carbon-neutral fuel scarcity issue,” says Paolo. A green shipping corridor is a route from one port to another where ships aim to maximize the use of carbon-neutral fuels earlier than required by existing legislation and regulation. Green corridors are designed to accelerate the early adoption of carbon-neutral fuels by resolving key barriers at a manageable scale. In addition to the high cost and low availability of carbon-neutral fuels, corridors tackle safety regulations and bunkering issues
“Engines are as clean as the fuels they use,” says Paolo. “If we can scale up the carbon-neutral fuel infrastructure, then highly efficient turbocharged engines will carry us into a new era of sustainable shipping.”
Dual fuel is gaining momentum as a bridge through the energy transition
The shipping industry has no time to lose on the path to decarbonization, and the rapid rise of dual fuel orders reflects the industry’s answer to that mandate, with dual fuel engines making up 50% of orders from January to September 2024, compared to 45% in 2023.1 Dual fuel engines are a pragmatic way for ship owners and operators to cut emissions now, while they continue to fulfill their vital role in global trade, and sail into a future where there are enough carbon-neutral fuels for all.