(CVBreard) wrote

Jet fuel used be be JP-4 (I believe there was also a JP-5,
perhaps others), and is now Jet A. What are the differences?

Charlie...almost everything you ever wanted to know about jet
fuel thanks to the miracle of OCR and Pratt & Whitney. :-)

Bob Moore

Military Fuels
The fuels used in gas turbine engines by the military services have
been given the prefix, "JP." A brief review of these fuels will
illustrate the evolution that has taken place in the development of
aircraft-gas-turbine fuels since the engines were first introduced.
The JP-1 and JP-2 fuels are no longer available, as such.

JP-1 was a kerosene-type of fuel of low freezing point. Because the
low freezing-point (-76°F) requirement made procurement difficult,
production of this fuel was rather limited.

JP-2 was somewhat more volatile than JP-1, but was never used
extensively. The specification was written late in World War II, as
a means of relieving a potential shortage of JP-1.

JP-3 was developed as a fuel of maximum availability, and was, as a
result, more volatile than JP-2. Because of its volatility, great
losses were experienced in flight through evaporation at high
altitude and during high rates of climb.

The specification for JP-4 was issued in 1951. The fuel has a
desirable, lower volatility than JP-3, but was, at first, a step
backward toward JP-2, because the JP-4 specification was more
restrictive as far as availability was concerned. Later, some of
the properties of the fuel, other than volatility, were altered to
ease the supply-situation.

JP-5 was developed as a heavy kerosene to be used as a product to
be blended with gasoline to produce a fuel similar to JP-4. This
procedure was desirable for naval operation aboard aircraft
carriers where only limited storage space was available for the
necessarily large quantities of JP-4. The JP-5 fuel could be
blended, as needed, with the supply of aviation gasoline carried
aboard ship for aircraft powered with reciprocating engines. The
JP-5 could be stored in any available tanks normally used for the
ship's diesel-engine fuel. In emergencies, it was also possible to
use the JP-5 in the ship's own engines. However, as aircraft-gas-
turbine development progressed, even JP-4 became too volatile for
some operations, so engines were designed to use JP-5 directly. The
JP-5 has a high flash-point (140°F) and very low volatility
characteristics.

JP-6 was developed by the Air Force for land-based, high-speed,
supersonic aircraft. The fuel is slightly more volatile than JP-5,
and has a low freezing point (- 65'F) for aircraft operation in
cold climates and at high altitudes.

Commercial Fuels
When it was assured in 1956 that gas turbine engines would be used
in commercial aircraft, it became evident that a definition was
needed for a fuel suitable for commercial airline operation. The
American Society for Testing Materials (A.S.T.M.) has published two
specifications defining grades of fuel suitable for commercial-gas-
turbine-engine use. The first is known as the "A" Specification,
and is for a kerosene-type fuel, not unlike JP-5. The A.S.T.M. "B"
Specification is for a JP-4 type of fuel. Pratt & Whitney Aircraft
has issued a specification, designated PWA 522, which defines the
properties needed in the fuel for the Pratt & Whitney Aircraft
axial-compressor engines which power commercial turbojet and
turbofan airliners and business aircraft. The requirements of the
PWA 522 specification, together with any additional requirements
desired by individual airlines, will provide an adequate
specification for various commercial airline operators to employ
when purchasing gas-turbine fuel. In all likelihood, each operator
will use a slightly different purchase-specification to suit the
needs of his particular operation. Commercial-gas-turbine-engine
fuel will therefore embody a range of volatility characteristics,
similar to that encompassed by both the JP-4 and JP-5 military
fuels.