Wednesday, January 28, 2009

Aviation Fuel

Aviation Turbine Fuel

Jet propulsion can be traced back to the 1st century B.C. when an Egyptian, Hero, is credited with inventing a toy that used jets of steam to spin a sphere. Sixteen centuries later, Leonardo da Vinci sketched a device that used a flux of hot gas to do mechanical work. By the 17th century, inventors were beginning to develop simple turbine systems to operate machinery.

The development of a turbine engine for aircraft began independently in Germany and Britain in the 1930s. In Germany, Hans von Ohain designed the engine that powered the first jet flight in 1939. Germany deployed the jet-powered Messerschmitt 262 late in World War II.

In Britain, Frank Whittle obtained a patent for a turbine engine in 1930. An aircraft powered by an engine he designed first flew in 1941. The first British jet fighter, the Gloster Meteor, also flew late in World War II.

T Y P E S O F F U E L

Illuminating kerosene, produced for wick lamps, was used to fuel the first turbine engines. Since the engines were thought to be relatively insensitive to fuel properties, kerosene was chosen mainly because of availability; the war effort required every drop of gasoline.

After World War II, the U.S. Air Force started using “wide-cut” fuel, which, essentially, is a hydrocarbon mixture spanning the gasoline and kerosene boiling ranges. Again, the choice was driven by considerations of availability: It was assumed that a wide-cut fuel would be available in larger volumes than either gasoline or kerosene alone, especially in time of war.

However, compared to a kerosene-type fuel, wide-cut jet fuel was found to have operational disadvantages due to its higher volatility:

  • Greater losses due to evaporation at high altitudes.
  • Greater risk of fire during handling on the ground.
  • Crashes of planes fueled with wide-cut fuel were less survivable.

So the Air Force started to change back to kerosene-type fuel in the 1970s and has essentially completed the process of converting from wide-cut (JP-4) to kerosene-type (JP-8) system-wide. The U.S. Navy has used a high flashpoint kerosene-type fuel (JP-5) on aircraft carriers because of safety considerations since the early 1950s. See Figure 3.1 for a list of U.S. military jet fuels.

When the commercial jet industry was developing in the 1950s, kerosene-type fuel was chosen as having the best combinations of properties. Wide-cut jet fuel (Jet B) still is used in some parts of Canada and Alaska because it is suited to cold climates. But kerosene-type fuels – Jet A and Jet A-1 – predominate in the rest of the world.

Jet A is used in the United States while most of the rest of the world uses Jet A-1. The important difference between the two fuels is that Jet A-1 has a lower maximum freezing point than Jet A (Jet A: - 40°C, Jet A-1: - 47°C).

The lower freezing point makes Jet A-1 more suitable for long international flights, especially on polar routes during the winter. However, the lower freezing point comes at a price. Other variables being constant, a refinery can produce a few percent more Jet A than Jet A-1 because the higher freezing point allows the incorporation of more higher boiling components, which in turn, permits the use of a broader distillation cut. The choice of Jet A for use in the United States is driven by concerns about fuel price and availability. Many years of experience have shown that Jet A is suitable for use in the United States, especially for domestic flights.

F U E L C O N S U M P T I O N

The consumption of jet fuel has more than doubled in the United States over the past 25 years, growing from 32 million gallons per day in 1974 to 70 million gallons per day in 1999. Most of this growth has occurred since 1984.

Data for the worldwide use of jet fuel are available only for years after 1989 (see Figure 1.2). In 1998, the most recent year for which data are available, consumption was 178 million gallons per day, up 13 percent from 1990. Figure 1.2 shows how this total is distributed around the globe. The United States is the largest single market by far, consuming about 38 percent of the worldwide total.

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