Katerina Swanson
Jet fuel and diesel fuel are both fractional distillates of petroleum fuel oil, and while they have a lot in common, there are some key differences in their composition and application. Jet fuel is considered a high-sulphur fuel, and while it has a higher sulphur content than diesel fuel, sulphur compounds may be helping to cool the planet by forming clouds that reflect sunlight back into space. Jet fuel is also dryer than diesel fuel, and while it has a higher flash point, it has a very low freezing point. Diesel fuel, on the other hand, tends to freeze or form wax crystals at low temperatures, which can block filters and stall engines—a particular problem for aircraft flying at high altitudes.
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What You'll Learn
Jet fuel has higher sulphur content than diesel
Jet fuel and diesel fuel are developed from the same base petroleum distillate, but have different additives to make them their specific fuel type. Jet fuel, especially Jet-A type, is considered a high-sulphur fuel. It has higher sulphur content than diesel fuel, and much higher than gasoline. Sulphur compounds are linked to asthma and breathing disorders.
While jet fuel is considered to have higher sulphur content, diesel fuel has been found to produce more nitrogen oxides, which are also linked to asthma and breathing disorders. There is growing evidence that the health and environmental costs of nitrogen compounds in diesel outweigh the benefits of lower CO2 levels.
The specifications of jet fuel are designed to improve the safety and reliability of flight. For example, no blending of fatty acid methyl esters, as used in diesel, is permitted in jet fuel due to risks to low-temperature properties, impact on aircraft range, and fuel stability. Diesel specifications, on the other hand, are set on a more local level and can vary considerably in content.
The low popularity of diesel aircraft engines can be attributed to the comparatively low power-to-mass ratio of diesel engines. Diesel engines are usually heavy, and as they produce more power, they also become heavier. This is a significant disadvantage for aircraft.
In conclusion, while jet fuel has higher sulphur content than diesel, the overall environmental and health impacts of diesel fuel are currently a greater cause for concern, with a push for alternative fuel types to reduce pollution.
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Jet fuel is designed for gas-turbine engines
Jet fuel, also known as aviation turbine fuel (ATF) or avtur, is specifically designed for aircraft powered by gas-turbine engines. It is a colourless to straw-coloured mixture of various hydrocarbons, with Jet A, Jet A-1, and Jet B being the most commonly used types for commercial aviation. Jet fuel is defined by its performance specifications, such as freezing and smoke points, rather than its chemical composition, which can vary based on the petroleum source.
The development of jet fuel specifications by the aviation industry prioritises the safety and reliability of flight. These specifications ensure that the fuel maintains its quality during transport and storage and that any additives are strictly regulated. For example, jet fuel does not contain fatty acid methyl esters, which are used in diesel, to prevent issues with low-temperature properties, aircraft range, and fuel stability.
Jet fuel is utilised in gas-turbine engines, which can operate with a wide range of fuels due to the injection of fuel directly into the hot combustion chamber. Turbine engines typically use lower-cost fuels with higher flash points, which are less flammable and safer to handle and transport. The Junkers Jumo 004 axial compressor jet engine, for instance, used in the Messerschmitt Me 262A fighter, employed this principle.
Additionally, jet fuel is used in military applications, with the United States and other NATO nations primarily consuming jet fuels designated as JP, which stands for "Jet Propellant." These fuels are complex mixtures of aliphatic and aromatic hydrocarbons, derived from crude oil and/or kerosene, and enhanced with various additives. JP-8, a kerosene-based fuel, is considered a "universal fuel" by the United States military, powering both turbine-driven aircraft and diesel-powered ground vehicles.
While jet fuel is designed for gas-turbine engines, it is important to note that advancements in alternative fuels, such as aviation biofuel and synthetically created fuel ("e-jet"), collectively termed "Sustainable Aviation Fuel" (SAF), are being explored as replacements for conventional aviation fuel. These alternatives aim to reduce the environmental impact of aviation by providing sustainable options that are compatible with existing combustion engines and infrastructure.
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Diesel is heavier than avgas engines
There are two primary fuels in use in aviation: avgas and Jet-A. They are similar in nature to automotive fuel (unleaded gasoline) and diesel, respectively, but have some key differences in both their properties and applications in aviation.
Avgas is an ignition fuel, which means it requires a spark or other ignition source to burn. It is used in piston engine aircraft. On the other hand, aero-diesel engines are heavier than avgas engines because they are partly made of steel, and they are turbocharged, which adds weight. However, aero-diesel engines do not need magnetos, which saves some weight.
Another key difference is that avgas contains lead in the form of Tetra Ethyl Lead (TEL), which is extremely toxic and expensive to deal with. Without the lead, avgas engines can experience self-detonation at high-density altitudes, which can be deadly. This is a significant issue for aircraft that fly at high altitudes. In contrast, diesel fuel can freeze or form wax crystals at low temperatures, blocking filters and stalling engines, which is problematic for aircraft flying in cold conditions.
While aero-diesel engines may produce less CO2 than avgas engines, there is uncertainty around this due to a lack of data. Additionally, diesel engines produce more nitrogen oxides and sulphur compounds, which are linked to asthma and breathing disorders. Jet fuel has a higher sulphur content than diesel, which may contribute to cooling the planet through cloud formation. However, the environmental and health costs of diesel's particulates, nitrogens, and sulphur compounds may outweigh the benefits of lower CO2 levels.
In summary, while diesel may have some advantages over avgas in terms of CO2 emissions and the absence of lead, it also has several drawbacks, including higher weights, greater nitrogen oxide and sulphur compound emissions, and freezing issues at low temperatures.
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Jet fuel has a higher flash point than gasoline
Jet fuel has been developed by the aviation industry with safety and reliability in mind. Jet fuel has a higher flash point than gasoline, which means it is less flammable and therefore safer to transport and handle. The flash point of a material is the "lowest liquid temperature at which, under certain standardized conditions, a liquid gives off vapours in a quantity such as to be capable of forming an ignitable vapour/air mixture".
The higher flash point of jet fuel is a result of its kerosene base, which was derived from standards for kerosene use in lamps in the UK (known as paraffin). Jet A and Jet A-1, the most common types of jet fuel, have a flash point higher than 38 °C (100 °F). In comparison, aviation gasoline has a lower flash point and a higher autoignition temperature to prevent pre-ignition in high-compression aircraft engines.
The use of jet fuel with a higher flash point is particularly important for aircraft carriers, as it reduces the risk of fuel ignition during transport and storage. Turbine engines, including those in jet and gas turbine aircraft, can operate with a wide range of fuels due to the injection of fuel directly into the hot combustion chamber. This allows for the use of jet fuel with a higher flash point, which is safer but also has a lower energy density.
The higher flash point of jet fuel also has implications for its freezing point. Jet fuel typically has a very low freezing point, with some types having a freezing point of −60 °C (−76 °F). The low freezing point improves the cold-weather performance of jet fuel, making it suitable for use in extremely cold regions such as northern Canada and Alaska. However, a very low freezing point can also reduce the availability of fuel, as it is more challenging to produce and store.
While jet fuel has a higher flash point than gasoline, it is important to consider other factors when comparing their environmental impacts. Jet fuel has a higher sulphur content than diesel fuel and gasoline, which can contribute to the formation of acidic clouds that reflect sunlight back into space. Additionally, diesel engines produce more nitrogen oxide compounds, which are linked to asthma and breathing disorders. The push for alternative fuels, such as aero-diesel or completely lead-free options, aims to balance performance, cost, and environmental considerations.
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Diesel specifications are set on a local level
Diesel fuel is a liquid fuel specifically designed for use in internal combustion engines, which are known as diesel engines. In these engines, fuel ignition occurs without a spark, as a result of the compression of inlet air and the subsequent injection of fuel.
The variability in diesel specifications on a local level is influenced by several factors, including refinery ability, market demand, government regulation, seasonal requirements, and economic considerations. For example, in the past, diesel fuel contained higher quantities of sulphur. However, due to European emission standards and preferential taxation, oil refineries have significantly reduced sulphur levels in diesel fuels. As a result, ultra-low-sulfur diesel (ULSD) has become the standard in many regions, including the United Kingdom, mainland Europe, and North America.
The regional variations in diesel specifications lead to differences in the composition and quality of fuels used in various markets, ultimately impacting vehicle performance and emissions. These specifications are vital for engine performance, fuel economy, and emission control, promoting market consistency and consumer confidence. Compliance with diesel specifications is crucial to prevent engine damage, enhance combustion efficiency, and ensure environmental sustainability.
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Frequently asked questions
Jet fuel and diesel are both specific fractional distillates of petroleum fuel oil. However, jet fuel is designed for gas-turbine engines in aircraft, while diesel is designed for engines in ground transportation vehicles. Jet fuel is dryer and has lower lubricity compared to diesel fuel. Diesel fuel often requires lubricity additives to ensure the long-term functionality of the injector system. Jet fuel also has a higher flash point than diesel.
It is not clear whether jet fuel or diesel is cleaner. Jet fuel has higher sulfur content than diesel fuel, which is linked to asthma and breathing disorders. However, jet fuel does not contain blending of fatty acid methyl esters, which are used in diesel. Jet fuel specifications are also more strictly regulated than diesel, which can vary considerably in content depending on factors such as refinery ability and market demand.
Yes, jet fuel is sometimes used as an additive in diesel fuel. It is marketed as a fuel injector cleaner due to its high volatility. However, the effectiveness of jet fuel as a diesel additive is questionable, as the small amount used may not have a significant impact.
