The Effects of Particulate Matter on the Thermal Stability of Jet Fuel

It is estimated that 26 billion gallons of jet fuel are used every year in the United States. The ability of fuel to withstand heat, otherwise called its thermal stability, is of primary concern to the industry, and the effects of particulate matter are being investigated. Particulate matter and thermal stability are interrelated, as one generally influences the other.

Thermal Stability

• Thermal stability is a measure of the amount of heat jet fuel can be exposed to before it oxidizes. As aircrafts are upgraded to improve fuel consumption, the thermal stability of fuel used also requires improvement. It is also a requirement because of the fact that the quantity of heat produced increases with flight velocity. Additionally, jet fuel absorbs excess heat from cooling aircraft components such as engine oil, which leads to fuel oxidation.

Particulate Matter

• At temperatures above 163 degrees C, jet fuel oxidizes, giving rise to particulate matter deposits. Approximately 7 million lbs. of particulate matter are released each year by U.S. aircrafts. Examples of particulate matter include carbon and organic sulfur compounds such as sulfides and disulfides. Particulate matter is a direct occurrence of thermal instability and contributes to more instability by stimulating jet fuel oxidation.

Improving Thermal Stability

• Reducing the deposition of particulate matter greatly improves thermal stability, and vice versa. Thermal stability of jet fuel is usually modified by chemical additives, which also help remove particulate matter contaminants. The JP-8C+100 additive is reported to reduce particulate matter deposits by up to 95 percent. Antioxidant additives are added to fuel to prevent the formation of particulate matter such as peroxides and other free radicals, which in turn improves thermal stability.

Problems

• Despite successes, most additives are considered insufficiently effective at decreasing particulate matter. Researchers from the U.S. Air Force investigated the efficiency of 17 commercially available additives and found that all were substandard at reducing particulate matter deposits. Some chemical additives even further contribute to the presence of particulate matter when they themselves become oxidized, thus reducing their impact on improving the thermal stability of jet fuel.