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THE HISTORY OF THE JET ENGINE Sir Frank Whittle : Was an English aviation engineer and pilot, the son of a mechanic, Whittle joined the Royal Air Force or RAF as an apprentice. He later became a pilot after training at the RAF College, Cranwell. He joined an RAF fighter squadron in 1928. The young RAF officer was only 22 when he first thought to use a gas turbine engine to power an airplane. born: June 1, 1907, Coventry, Warwickshire, England died: Aug. 8, 1996, Columbia, Md., U.S. Doctor Hans Joachim Pabst von Ohain : Was a German airplane designer, who invented an operational jet engine. Ohain obtained his doctorate at the University of Göttingen in Germany. He was the junior assistant to Hugo von Pohl, director of the Physical Institute at the University. German aircraft builder Ernst Heinkel asked the university for assistance in airplane design and Pohl recommended his star pupil Ohain. born: Dec. 14, 1911 , Dessau, Germany died: March 13, 1998, Melbourne, Fla., U.S. A jet engine operates on the application of Sir Isaac Newton's third law of physics: for every action there is an equal and opposite reaction. This law is demonstrated in simple terms by releasing an inflated balloon and watching the escaping air propel the balloon in the opposite direction. In the basic turbojet engine, air enters the front intake and is compressed, then forced into combustion chambers where fuel is sprayed into it and the mixture is ignited. Gases which form expand rapidly and are exhausted through the rear of the combustion chambers. These gases exert equal force in all directions, providing forward thrust as they escape to the rear. As the gases leave the engine, they pass through a fan-like set of blades (turbine) which rotates the turbine shaft. This shaft, in turn, rotates the compressor, thereby bringing in a fresh supply of air through the intake. Engine thrust may be increased by the addition of an afterburner section in which extra fuel is sprayed into the exhausting gases which burn to give the added thrust. At approximately 400 mph, one pound of thrust equals one horsepower, but at higher speeds this ratio increases and a pound of thrust is greater than one horsepower. At speeds of less than 400 mph, this ratio decreases. In a turboprop engine, the exhaust gases are also used to rotate a propeller attached to the turbine shaft for increased fuel economy at lower altitudes. A turbofan engine incorporates a fan to produce additional thrust, supplementing that created by the basic turbojet engine, for greater efficiency at high altitudes. The advantages of jet engines over piston engines include lighter weight with greater power, simpler construction and maintenance with fewer moving parts, and efficient operation with cheaper fuel. History of Jet Fuel The first simple jet engines were developed just prior to and during the early part of World War II. Hans von Ohain in Germany developed the first successful aviation turbine engine that flew in the Heinkel He 178 on 27 August 1939. Gasoline was the fuel used because of its ease of evaporation and known performance properties in piston engine aircraft. Across the English Channel Sir Frank Whittle also developed an aviation turbine engine which first flew in a Gloster E28/32 aircraft on 14 May 1941. Whittle's engine used illuminating kerosene since gasoline was in short supply because of the war. The Whittle engine became the forerunner of successful jet engines in both the US and Britain, and now, more than 50 years later, kerosene remains the primary jet fuel that powers the world's airlines and military fleets. Early proponents of the jet engine claimed that these new engines could operate on any fuel from whiskey to peanut butter. Although jet engines are much more tolerant than gasoline and diesel engines, the aircraft and engine fuel system are sensitive to the chemical and physical properties of the fuel. Early advances in engine and aircraft design greatly expanded the flight envelope which necessitated new standards for turbine engine fuel quality. This led to the introduction of a variety of fuel types for different purposes and to the development of specifications to ensure the fuel met equipment requirements under all flight conditions. In 1944 the US published specification AN-F-32 for JP-1, a -600C freezing point kerosene. The freezing point so limited availability that is was soon superseded by various wide cut fuels; JP-2 (1945), JP-3 (1947) and JP-4 (1951 - avtag, NATO F-40). These wide cut fuels are mixtures of naphtha and kerosene which greatly increase availability. The first British jet engine fuel specification, RDE/F/KER (Provisional), was introduced by the end of World War II and covered what was virtually an illuminating kerosene. After a few amendments, RDE/F/KER was superseded in 1947 by D.Eng.RD. (DERD) 2482 and this was in turn reissued from time to time with increasingly stringent requirements. This specification became obsolete in 1965 when it was replaced by D.Eng.RD 2494, the predecessor to current commercial (Defence Standard 91-91 and British military (Defence Standard 91-87) specifications. Even though the first US jet engines were direct copies of early British designs, these pioneering jet fuel specifications differed significantly in volatility, freezing point, specific gravity, sulfur and aromatic limits. The US specification was most likely derived from the aviation gasoline specification, while the British specification reflected the properties of illuminating kerosene. High flash point kerosene was introduced as early as 1948 to reduce the fire risk aboard aircraft carriers. The first specification for this grade was RDE/F/KER 203 and called for a flash point similar to light diesel fuel. The - 650C freeze point was later amended to -600C in D.Eng.RD 2488 as it was too restrictive. Defence Standard 91-86 (D.Eng.RD 2452) is the current British military specification for high flash kerosene. The first US Navy aircraft used aviation gasoline, but the lead in the fuel attacked the hot section components in the engine. One proposed approach was to blend aviation gasoline with kerosene to form Jet Mix, a product similar to JP-4. JP-5 (avcat, NATO F-44), a high flash point kerosene developed by the Navy for use in Jet Mix, was first covered by the specification MIL-F-7914 in 1952. Subsequently, JP-5 was included in MIL-F- 5624B in 1953. Although considerable work was done on Jet Mix, this product was never used operationally and JP-5 remains the primary jet fuel for most navies around the world. A kerosene fuel very similar to commercial Jet A-1 , was developed by the USAF to reduce the fire hazards associated with wide cut fuels which became apparent during the Southeast Asian conflict. JP-8 replaced JP-4 as the primary military jet fuel for USAF operations in Great Britain in 1979, and is currently the primary jet fuel for NATO. The USAF completed its conversion to JP-8 in 1995. JP-8 is covered by the specification MIL-DTL-83133 and British Defence Standard 91-87. Although JP-8 has replaced JP-4 in most every case, the potential need for JP-4 under emergency situations necessitates maintaining this grade in specifications MIL-DTL-5624 and Defence Standard 91-88. There are several other special military grades of aviation kerosene that exist today or have been made redundant for specific reasons. JP-6 was a kerosene fuel developed in 1956 for the XB-70 aircraft. JP-6 was similar to JP-5 but with a lower freezing point and improved thermal oxidative stability. The cancellation of the XB-70 program resulted in the cancellation of the JP-6 specification, Mil-J-25656. JPTS is a special purpose jet fuel developed in 1956 to power the high flying U-2 aircraft. JPTS is an extremely thermally stable jet fuel with a low freezing point to support this type of mission. JPTS, produced to specification MIL-DTL-25524, is still used today in the U-2 and the newer TR-1 aircraft. The development of the SR-71 in the late 1960s required a new fuel having low vapor pressure and excellent thermal oxidative stability to meet the requirements of high altitude and Mach 3+ cruising. JP-7 is not a distillate fuel like most other jet fuels, but is composed of special blending stocks to produce a very clean hydrocarbon mixture low in aromatics (typically 3%), and nearly void of the sulfur, nitrogen and oxygen impurities found in other fuels. The combustion characteristics are also tightly specified to ensure adequate combustor life. The JP-7 specification, MIL-DTL-38219, was first published in 1970.
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