Mercedes Mullins
The combustion of diesel fuel has been a topic of interest for scientists and engineers alike, who have been working on improving its efficiency and reducing harmful emissions. While diesel delivers greater energy efficiency than gasoline, it also releases toxic NOx emissions. Jet fuel, on the other hand, is developed by the aviation industry with specifications designed to improve safety and reliability. It is important to note that the comparison between diesel and jet fuel is not straightforward as they are used in different contexts and have distinct properties. So, which fuel burns cleaner, and what are the ongoing efforts to improve fuel efficiency?
Diesel vs Jet Fuel Characteristics
| Characteristics | Values |
|---|---|
| Flash point | Jet fuel has a higher flash point than Avgas. Jet fuel and diesel fuel have to be heated to greater than +38 and +55 °C respectively for the vapor to burn under ambient conditions. |
| Engine compatibility | Jet fuel is used in gas-turbine engines. Jet fuel can be used in diesel engines, but it has poor lubricating ability compared to diesel, which increases wear in fuel injection equipment. Diesel engines are uncommon in aircraft today. |
| Safety | Jet fuel specifications are designed to improve the safety and reliability of flight. Jet fuel is available in most places in the world, unlike Avgas. |
| Composition | Jet fuel is a mixture of different hydrocarbons. Jet fuel contains more sulfur than diesel, which gives it better lubricity. |
| Environmental impact | Jet fuel is often used in diesel-powered ground-support vehicles at airports. Jet fuel tends to be more expensive than diesel fuel. |
| Energy efficiency | Diesel combustion delivers greater energy efficiency than gasoline combustion. |
| Emissions | Diesel releases toxic NOx emissions. Soot emissions can be reduced by using Bunsen burner-inspired tubes for fuel injection. |
| Cold weather performance | Diesel may freeze or form wax crystals blocking filters and stalling engines at low temperatures. Kerosene is added to diesel fuel in cold weather to reduce the temperature at which it solidifies. |
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What You'll Learn
Kerosene is a cleaner-burning fuel than diesel
Kerosene, also known as #1 diesel fuel oil, is a lighter diesel oil than #2, which is regular diesel. Kerosene is distilled into a pure fuel, while diesel has a solid molecular structure. Kerosene is composed of hydrocarbon chains that contain 12 to 15 carbon atoms, while diesel has 16 carbon atoms. Kerosene has a lower lubricity than diesel, which can cause automotive mechanisms to experience wear and tear and burn out. Kerosene also has a lower energy value than diesel, producing about 135,000 BTU per gallon compared to 139,000 BTU for a gallon of #2 diesel.
Despite producing less heat, kerosene burns cleaner than diesel. Kerosene is frequently used at extremely cold temperatures since it does not thicken as easily as diesel. Kerosene is also less expensive than diesel due to the road taxes added to the price of diesel fuel. Kerosene has a higher flash point than diesel, meaning it requires higher temperatures for the vapour above the liquid fuel to catch fire. Kerosene's low carbon monoxide emissions mean there is a lower risk of carbon monoxide poisoning when using it.
Kerosene is often mixed with diesel fuel to reduce emissions and modify the cold-weather handling temperatures of diesel. Adding 10% kerosene to a diesel fuel blend lowers the cold filter plugging point by five degrees. Kerosene can also be used as a substitute for diesel in diesel engines during the winter, as it is less likely to gel in the cold. However, kerosene's lower lubricity can cause issues for fuel pumps, and its lower energy value can reduce the power and efficiency of engines.
While kerosene burns cleaner than diesel, it is not without its drawbacks. Kerosene contributes to greenhouse gas emissions and is a non-renewable oil that cannot be reused or recycled. Prolonged exposure to kerosene fumes can damage the skin and lead to lung diseases. Kerosene also has a persistent smell that can linger even after scrubbing.
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Jet fuel is designed to improve safety and reliability
Jet fuel is a type of aviation fuel designed for aircraft powered by gas-turbine engines. It is also used in propeller and jet fixed-wing aircraft and helicopters. Jet fuel specifications are designed to improve safety and reliability in flight. For instance, jet fuel has a higher flash point than gasoline-based fuel, meaning it requires a significantly higher temperature to ignite, making it safer in the event of a spill. Jet fuel is also designed to have a low viscosity at low temperatures, a limited range of density and calorific value, and to burn cleanly and remain chemically stable when heated to high temperatures.
Jet fuel is typically a mixture of various hydrocarbons, with the most commonly used types being Jet A and Jet A-1, which are produced to a standardized international specification. Jet B is another variety used for its enhanced cold-weather performance. Jet fuel is often kerosene-based, with Jet A-1 being an unleaded kerosene and Jet B being a naphtha-kerosene blend. Kerosene is a lighter diesel oil that burns cleaner than diesel fuel, producing fewer pollutants and lowering the risk of carbon monoxide poisoning.
To improve safety and reliability, jet fuel specifications also ensure that additives are strictly regulated. For example, no blending of fatty acid methyl esters, as used in diesel, is permitted in jet fuel due to the impact on low-temperature properties, aircraft range, and fuel stability. The development of jet fuel blends containing biofuel and synthetic jet fuels that reduce pollutants such as SOx, NOx, and particulate matter is also being explored.
In comparison to jet fuel, diesel fuel specifications are set on a more local level and can vary in content. Diesel fuel may freeze or form wax crystals that block filters and stall engines at low temperatures, which is a significant issue for aviators flying at high altitudes. While diesel engines have greater energy efficiency than gasoline engines, they release toxic NOx emissions, which can be minimized through a technique called dilution. However, this method does not consume all the fuel, resulting in partially burned carbon particles or soot.
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Diesel engines release toxic NOx emissions
Diesel engines are more fuel-efficient than petrol/gasoline engines, as diesel produces more energy for a given volume. However, diesel engines produce more harmful emissions than petrol/gasoline engines. One such harmful emission is NOx, which is a generic term for oxides of nitrogen, specifically nitric oxide (NO) and nitrogen dioxide (NO2). Nitrogen dioxide is a major pollutant and a component of smog, which irritates the eyes and respiratory tract. NOx emissions also affect ecosystems and agricultural crops.
There are various techniques to reduce NOx emissions from diesel engines. One method is Selective Catalytic Reduction (SCR), which is the most common approach in diesel vehicle exhausts. This method involves injecting proprietary blends of ammonia and urea into the exhaust flow, which react with NOx gases over a catalyst, turning them into harmless nitrogen and water. However, due to its expense, SCR is not used in small, cheap vehicles. Another technique is Selective Non-Catalytic Reduction (SNCR), which takes place at extremely high temperatures of around 1000°C (1800°F). At this temperature, urea or ammonia can be injected without the need for a catalyst, and the NOx gases are reduced to nitrogen.
Another strategy to minimize NOx emissions in diesel engines is dilution, where spent, low-oxygen combustion gases from the previous engine cycle are routed back into the air intake. This lowers the temperature and oxygen concentration in the fuel-air mixture, reducing the production of nitrogen oxides. However, this technique results in incomplete fuel combustion, leading to the formation of soot particles. This trade-off between soot and NOx emissions presents a long-standing challenge for diesel engine development.
To address this dilemma, researchers have explored methods to achieve complete combustion while maintaining low temperatures to minimize NOx formation. One innovative approach involves utilizing Bunsen burner-inspired fuel injection tubes in the diesel combustion chamber to promote better burning and reduce soot emissions. By premixing the fuel with air before ignition, the charge can burn at a lower temperature, potentially reducing the presence of soot particles.
While diesel engines produce toxic NOx emissions, ongoing research and the development of mitigation strategies demonstrate a commitment to reducing these harmful pollutants.
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Bunsen burner-inspired tubes may reduce soot emissions
The diesel combustion process is more energy-efficient than gasoline engines, but it releases harmful nitrogen oxide emissions (NOx) and soot particles. This has been a long-standing problem, and engineers have been trying to find a way to burn diesel fuel completely, thereby avoiding soot, while maintaining low temperatures to prevent excess nitrogen oxide.
Charles Mueller, a combustion scientist at Sandia National Laboratories, believes he has found a solution inspired by the Bunsen burner, a familiar lab-bench heater. Mueller's patented technology, called ducted fuel injection (DFI), involves placing small metal tubes, akin to tiny Bunsen burner chimneys, near the injector nozzle hole. This setup enables a more thorough premixing of fuel and air, resulting in a cleaner, soot-free, blue-flame burning at lower temperatures. The Bunsen burner, with its vertical tube, produces a clean blue flame when the tube is in place, as the burner consumes more of the fuel, reducing soot particles.
Mueller's DFI technology aims to address the soot-NOx trade-off, where lowering temperatures to minimise NOx leads to incomplete fuel combustion and increased soot. By promoting better burning, DFI has the potential to reduce soot emissions and decrease the need for exhaust aftertreatment systems, making diesel engines fundamentally cleaner.
While diesel engines have faced scrutiny due to their emissions, such as in the Volkswagen "Dieselgate" scandal, innovations like Mueller's DFI offer hope for reducing soot emissions and improving diesel's environmental footprint. The development of green replacements, such as electrochemical batteries and hydrogen fuel cells, is also underway, but they have yet to match diesel's power in the global economy.
In summary, Bunsen burner-inspired tubes show promise in reducing soot emissions from diesel engines by enhancing fuel-air mixing and enabling cleaner burning at lower temperatures. This innovation addresses a critical engineering challenge, bringing diesel engines a step closer to becoming truly clean.
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Kerosene is a lighter diesel oil than #2 diesel
Kerosene, also known as #1 diesel, is a lighter diesel oil than #2 diesel. It has a lower weight and energy content, with roughly 135,000 BTU per gallon compared to 139,000 BTU per gallon for #2 diesel. Kerosene is composed of hydrocarbon chains with 12 to 15 carbon atoms, while diesel has a solid molecular structure of 34 hydrogen and 16 carbon atoms.
Kerosene is less volatile than gasoline and has a higher flash point temperature of 100 degrees Fahrenheit. It is commonly used as a heating fuel and is known for its ability to maintain flow in cold temperatures, making it useful for changing the cold-weather handling temperatures of diesel fuel in winter. During the winter months, individuals often add a small amount of kerosene to their diesel fuel to reduce the temperature at which it solidifies.
Kerosene is also said to burn cleaner than #2 diesel, resulting in lower emissions and pollutants. This is because kerosene has a lower concentration of aromatic compounds, which are present in #2 diesel and heavier diesel fuel oils. However, kerosene contributes to greenhouse gas emissions and is non-renewable, meaning it cannot be reused or recycled.
One disadvantage of kerosene is its lack of lubricity, which can cause increased wear and tear on fuel pumps and other engine components. This can be mitigated by adding automatic transmission fluid or 2-cycle oil to the kerosene. Despite its cleaner-burning properties, propane is typically easier to locate and purchase than kerosene.
In summary, kerosene is a lighter diesel oil than #2 diesel with unique properties that make it useful for specific applications, particularly in cold climates. However, it also has environmental and maintenance-related drawbacks that should be considered.
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Frequently asked questions
Kerosene, which is the most common type of jet fuel, burns cleaner than diesel. Diesel fuel produces more BTUs (heat) than kerosene, but it has a larger paraffin/wax concentration.
Diesel fuel releases toxic NOx emissions and soot particles. Diesel also has a lower flash point than jet fuel, meaning it is more flammable. Diesel can also freeze or form wax crystals at low temperatures, blocking filters and stalling engines.
One way to make diesel burn cleaner is to fully combust the fuel, thus avoiding soot, while keeping temperatures low to avoid excess nitrogen oxide. Another method is to use fuel injection through Bunsen burner-inspired tubes, which can cut down on soot emissions.
