Jet fuel, primarily kerosene-based grades like Jet A and Jet A-1 used in commercial aviation, is defined by performance specifications rather than a single chemical formula. The temperature at which jet fuel burns is not a single number, but involves a range of thermal events from initiation to full combustion. These specifications govern distinct temperature thresholds that determine how the fuel behaves during handling, ignition, and sustained burning. Understanding these different temperatures is necessary to grasp the safety measures and operational physics involved.
Ignition Thresholds
The process of starting a jet fuel fire is governed by two distinct temperature points related to the fuel’s volatility and flammability. The flash point is the lowest temperature at which the fuel produces enough vapor to form an ignitable mixture with the air immediately above its surface. For Jet A and Jet A-1, this minimum temperature is 38°C (100°F), classifying it as a combustible liquid rather than a highly flammable one like gasoline. At this temperature, the vapor-air mixture will only ignite momentarily if an external source, such as a spark or flame, is applied.
A much higher temperature is required for the fuel to spontaneously ignite without any external ignition source, a point known as the autoignition temperature (AIT). For Jet A and Jet A-1, the AIT is approximately 210°C (410°F). This is the point where the fuel’s chemical components gain enough energy to react with oxygen on their own. This substantial difference between the flash point and the AIT is why kerosene-based jet fuel is considered relatively safe to handle compared to more volatile fuels.
Sustained Flame Temperature
Once the fuel is fully ignited and burning stably, the resulting flame temperature is significantly higher than either ignition threshold. The theoretical maximum heat a jet fuel flame could produce is known as the adiabatic flame temperature, which assumes perfectly efficient combustion with no heat loss. For kerosene-air combustion, this theoretical temperature is extremely high, often calculated to be in the range of 2,093°C to 2,210°C (3,800°F to 4,000°F).
In real-world scenarios, such as a spill fire burning in open air, the sustained flame temperature is much lower due to heat radiation, convection, and incomplete combustion. Open jet fuel fires typically generate temperatures between 815°C and 1,090°C (1,500°F and 2,000°F). This lower range occurs because the fire is often fuel-rich, meaning there is insufficient oxygen for complete burning, which results in characteristic black smoke. Inside a jet engine’s combustion chamber, however, the gas temperature is intentionally regulated to be much hotter, often exceeding 1,500°C to maximize efficiency and thrust.
Factors Influencing Combustion
The specific temperatures involved in jet fuel burning are not fixed values but fluctuate based on the fuel’s exact composition and the surrounding environment. Fuel composition directly influences volatility, as seen in the wide-cut Jet B fuel, a blend of kerosene and gasoline used in very cold climates. Because of the lighter, more volatile gasoline fraction, Jet B has a much lower flash point, sometimes as low as -18°C (-4°F). This enhances its cold-weather performance but requires more careful handling than Jet A.
External atmospheric conditions also play a significant role in modifying both the ignition and sustained burn temperatures. At high altitudes, reduced air pressure and lower oxygen concentration inhibit the initiation of combustion, making the air-fuel mixture harder to ignite. The sustained flame temperature is also significantly affected by confinement, as seen in highly energetic jet fires caused by pressurized leaks. When jet fuel burns in a confined space, greater heat retention can lead to localized flame temperatures approaching 1,350°C and causing rapid structural damage.