Boat Fuel Chemistry: Understanding The Chemical Composition

Boat fuel is a broad term for the gasoline used in boats, with the specific type depending on the engine in the vessel. The most common types of boat fuel are ethanol-free gasoline, oil and gas mixtures, and marine gas oil (MGO) or marine diesel oil (MDO). The type of fuel used can have a huge impact on the performance and longevity of a boat. For example, ethanol-free gasoline protects the condition of a boat's engine and extends its life, but it is more expensive than other fuel types. On the other hand, E10 fuel (10% ethanol) is safe for most boat engines and helps to reduce hydrocarbon emissions, but it can corrode rubber and fibreglass and clog fuel lines. Diesel fuel is another option, mainly used for larger boats as it provides increased torque and horsepower.

Ethanol-free gasoline

One of the main advantages of using ethanol-free gasoline in boats is that it does not have the corrosive effects associated with ethanol-containing gasoline. Ethanol can quickly corrode rubber and fiberglass, leading to degraded fuel lines and other components. Additionally, ethanol attracts water into the fuel system through "phase separation," resulting in internal corrosion, erosion of fiberglass, and uneven performance. Therefore, ethanol-free gasoline can provide better performance and a longer lifespan for boat engines.

However, there are some downsides to using ethanol-free gasoline. It is more expensive than E10 or other types of gasoline. Additionally, ethanol-free fuel uses the octane enhancer additive methyl tert-butyl ether (MTBE) to produce cleaner exhaust. Combining MTBE with ethanol from other fuel types can cause a gummy residue, leading to clogged fuel filters and performance issues. As a result, it is crucial not to mix ethanol-free gasoline with other types of gasoline. Switching between gasoline types may require a thorough cleaning of fuel tanks and lines.

Oil and gas mixtures

It is important to note that oil should only be mixed into the fuel for specified engines. Most larger, modern boat engines have separate lubrication systems, eliminating the need for oil-gas mixtures. For engines that require oil-gas mixtures, it is crucial to refer to the owner's manual for exact mixing ratios, as these can vary depending on the particular model. Common mixing ratios (gas:oil) include:

• 25:1 (typically during the break-in period)
• 50:1
• 100:1

To achieve these ratios, basic math is required. For example, a 50:1 gas:oil ratio would mean using 2.6 fluid ounces of oil per gallon of gas added to the fuel tank. For a 25:1 ratio, you would use 5.2 fluid ounces of oil per gallon of gas, and for a 100:1 ratio, you would use 1.3 fluid ounces of oil.

It is essential to find the correct ratio of oil to fuel to prevent issues such as smoking motors, hiccuping performance at high RPMs, and even significant internal damage. Adding too much or too little oil can be detrimental to the engine's performance and longevity. Therefore, many boaters pre-mix their gasoline before filling up to avoid imbalances.

When mixing oil and gas, it is recommended to use only marine oil that meets the TC-W standard. This type of oil is specifically designed for the demands of the marine environment, including higher RPMs and proximity to water sources. It ensures the best performance and longest life for 2-stroke engines.

Sulphur fuel

Sulphur is a common component of marine fuel, and its presence has important implications for both environmental sustainability and human health.

In 2020, the International Maritime Organization (IMO) introduced stricter regulations on the amount of sulphur allowed in marine fuel, limiting sulphur emissions to 0.5% for all ships operating worldwide. This followed an earlier, more limited restriction that applied only to ships operating in North American and North Sea coastal waters between 2010 and 2015. The IMO's more recent regulation has significantly reduced air pollution from ships, cutting total sulphur oxide emissions by 70% and bringing about cleaner air in ports and coastal areas.

Sulphur is a natural component of crude oil, and its by-product, sulphur dioxide (SO2), is released into the atmosphere when marine fuel is burned. Heavy Fuel Oil (HFO), used by most ships in service today, is relatively inexpensive but has a high sulphur content and can emit up to 3.5% sulphur oxide. The high sulphur content of marine fuel contributes to an estimated 19,000 to 91,000 premature deaths each year in coastal regions. Shipping air pollution is estimated to cause around 50,000 premature deaths per year in Europe alone.

The IMO's regulations aim to address these health and environmental concerns by reducing the maximum permitted sulphur content in marine fuel. Very-low sulphur fuel, often referred to as Marine Diesel Oil (MDO), is created by blending refinery residues with low-sulphur distillates, while Ultra-low sulphur fuel, or Marine Gas Oil (MGO), is a distillate fuel that has been through a refining process. These fuels are more expensive and can be unstable when mixed with other fuels, but they help reduce harmful emissions.

While the shift to low-sulphur marine fuel has benefits for human health, it has also had an unintended impact on global warming. Sulphur particles in ship exhaust fumes have been counteracting some of the warming effects of greenhouse gases. By reducing the sulphur content of marine fuel, the "masking effect" of these particles has been weakened, contributing to an increase in global temperatures. This side effect of the IMO's clean air regulations is estimated to increase global temperatures by around 0.05°C by 2050, equivalent to approximately two additional years' worth of emissions.

Diesel

• Particulates not otherwise regulated
• Benzene
• Formaldehyde
• 3'-Hydroxyacetophenone
• 2-Hydroxy-4-methoxyacetophenone
• 3-Methyl-2-cyclopentene-2-ol-one
• Trimethylbenzene (mixed isomers)
• Polynuclear aromatic hydrocarbons
• Benzo [b]fluoranthene
• Benzo [k]fluoranthene
• Coal tar pitch volatiles
• Dibenz [a,h]anthracene
• Indeno [1,2,3-cd]pyrene

Biodiesel, a renewable and clean alternative energy source, can be blended with diesel fuel to improve its characteristics. Biodiesel has excellent lubricity, superior biodegradability, and high combustion efficiency. Blending biodiesel with diesel fuel can reduce toxic pollutants and greenhouse gas emissions. It also helps lower the sulfur content of the fuel, which is particularly beneficial for high-sulfur fishing boat fuels.

Gasoline

Ethanol-free gasoline offers better performance and a longer lifespan for boat engines. However, it is more expensive than E10 and other types of gasoline. It uses the octane enhancer methyl tert-butyl ether (MTBE) to produce cleaner exhaust. Combining MTBE with ethanol from other fuel types can cause clogged fuel filters and performance issues, so it is essential not to mix ethanol-free gasoline with other types.

Overall, the use of gasoline in boats comes with specific considerations, and boat owners need to be mindful of the potential issues associated with different types of gasoline to ensure optimal performance and engine longevity.

Frequently asked questions