What is Gel? The Marine Fuel Revolution Explained

When Wärtsilä introduced gel fuel technology to the maritime industry, it marked a quiet but significant shift in how vessels could operate more efficiently and sustainably. Gel, in the context of marine propulsion, refers to a specially formulated fuel that combines heavy fuel oil with water and emulsifying agents to create a stable, homogeneous mixture. This innovation has gained traction among shipowners seeking cleaner combustion, reduced emissions, and improved engine performance without requiring extensive vessel modifications.

Understanding Gel Fuel Composition and Properties

Gel fuel is fundamentally different from conventional marine fuels. The formulation typically contains 50 to 70 percent heavy fuel oil, 20 to 40 percent water, and a small percentage of emulsifying additives that keep the mixture stable and prevent separation. The water content is the key differentiator—when properly emulsified, it doesn’t phase-separate or cause the corrosion problems that free water would create in fuel tanks.

The viscosity of gel fuel falls between that of traditional heavy fuel oil and marine diesel oil, making it suitable for use in medium-speed diesel engines without requiring fuel heating systems as complex as those needed for conventional HFO. This property alone has attracted significant interest from operators of smaller and medium-sized vessels. The fuel’s density and flow characteristics have been engineered to work seamlessly with existing fuel injection systems on compatible engines, though not all powerplants can burn gel without modification.

What makes gel particularly attractive is its combustion behavior. The water content, when properly dispersed, undergoes microexplosions during the combustion process. These tiny explosions improve fuel atomization and mixing, leading to more complete combustion. The result is reduced particulate matter emissions, lower nitrogen oxide levels, and decreased fuel consumption compared to straight heavy fuel oil burning.

Real-World Applications and Industry Adoption

Gel fuel has found its strongest foothold among tugboat operators, offshore supply vessels, and other working boats that operate in environmentally sensitive waters or near populated coastal areas. These vessel types benefit most from gel’s emission reduction profile without needing to invest in scrubber systems or switching to more expensive marine gasoil.

Several European and Asian shipping companies have conducted extensive trials with gel fuel over the past decade. The results have been encouraging enough that some operators now run gel as their standard fuel choice for certain routes or operational profiles. Wärtsilä’s own research documented fuel consumption reductions of up to 5 percent in some applications, along with measurable improvements in air quality metrics around ports where gel-burning vessels operate.

The regulatory environment has also influenced gel adoption. As International Maritime Organization regulations tightened around sulfur content and emissions, gel presented an alternative compliance pathway for operators who didn’t want to retrofit scrubbers or switch to distillate fuels entirely. In regions with strict local air quality standards—particularly around major ports in Northern Europe and parts of Asia—gel fuel offers a middle ground between cost and environmental performance.

Challenges and the Path Forward

Despite its advantages, gel fuel hasn’t achieved widespread adoption across the global fleet. The primary barrier remains infrastructure. Gel fuel requires specialized handling, storage, and supply systems. Not every port has the capability to supply it, and vessels need compatible fuel treatment systems to handle the water content safely. Engine compatibility is another consideration—while many modern medium-speed engines can burn gel, older tonnage often cannot without significant modification.

The economics also matter. Gel fuel pricing hasn’t consistently undercut heavy fuel oil, particularly when fuel oil prices drop. Without a clear cost advantage, many operators default to conventional fuels, especially on long-haul routes where fuel represents a massive operating expense.

Looking ahead, gel fuel occupies an interesting position in the maritime energy transition. It’s neither a short-term solution like scrubbers nor a long-term answer like ammonia or hydrogen. Instead, gel represents a practical optimization tool for operators seeking incremental emissions reductions while maintaining compatibility with existing engine technology. As the industry continues its gradual shift toward cleaner fuels, gel will likely remain relevant for specific vessel types and routes where its particular combination of performance, cost, and environmental benefits aligns with operational requirements.