Combustion

Part 9 - Turbines

Jet engines can be dated back to the invention of the aeolipile, around 150 BCE, which used steam jets directed through two nozzles to cause a sphere to spin rapidly on its axis.

English engineer John Barber patented the first detailed description of a gas turbine between 1766 and 1792 although it was not a practical design. 

Sir Charles Algernon Parsons was head of electrical equipment development for a maker of ship engines in 1884 when he developed a steam turbine engine to drive an electrical generator. (Today about 80% of the world's electrical supply is generated by steam turbines).

Parsons realized that steam turbine would revolutionize shipping. Turbines were more efficient than the huge, complicate, reciprocating steam engines used to drive ships at the time. Turbines were more powerful, more efficient, faster, weighed less, had less vibration and were cheaper to make.

But, Parsons was not able to convince conservative ship owners so he built the steam ship Turbinia, in 1894.  It was 100 feet long, 9 feet wide and displaced 44 tons.  Parsons connected three turbines using the exhaust steam from one to drive the next.  This triple expansion system provided 2,100 horsepower to drive three shafts with triple propellers on each shaft.   Now all he needed was a good place for a demonstration.

In June, 1897, in honour of her 60th year on the throne, Queen Victoria reviewed the Royal Navy near Portsmouth.  Just as her son, Edward, the Prince of Wales, appeared and the band played the national anthem, Turbinia sped into the passing review at 34 knots. A Royal Navy picket boat, sent to intercept, was nearly sunk in Turbinia's wake. The stunt generated interest and, in 1905, the first turbine-powered North Atlantic liners were built. They were the 12,000-ton Virginian and Victorian. In 1906, the warship HMS Dreadnought was launched with Parsons turbines and within 12 years, all first line ships in the Royal Navy were powered by steam turbines.

Since the 1980s, most ships have been fitted with diesel engines because of their greater efficiency. But fast warships now use auxiliary gas turbines to provide greater speed when required. Steam turbines are still used by nuclear powered ships and submarines and liquid natural gas (LNG) carriers (which burn evaporating natural gas to generate steam).

William Ægidius Elling, a Norwegian inventor, who built the first practicable gas turbine in 1903, used a rotary compressor and turbine to produce 11 bhp (brake horse power) (8 kW). Finding materials that could withstand the high temperatures needed achieve high output powers was a problem. His 1903 turbine could withstand inlet temperatures up to 400° Celsius (752° F). Elling understood that if better materials could be found, the gas turbine would be an ideal power source for aircraft.

Piston engines were the only source of power suitable for aircraft, in the 1930s, but engineers knew that propulsive efficiency declined as propeller blade tips approached the speed of sound. They began to develop other power sources and one of these was the gas turbine (jet) engines.

The jet engine required a gas turbine to drive an air compressor but there were many problems with engineering design. The engines had to be light, safe and reliable. Gas turbine blades and bearings had withstand extreme dynamic loads at high temperatures for long periods.

Maxime Guillaume obtained a French patent, for an axial-flow gas turbine to power an aircraft, in 1921 but it was never made.

Dr. Albert Fonó, a Hungarian mechanical engineer and a pioneers of ramjet propulsion and turbojet engines, was first to be granted German patents in 1932.

In 1935 Germany, Hans von Ohain developed a gas turbine design. The prototype needed external power to run but he was able to demonstrate the concept to the Ernst Heinkel who formed a new division of his aircraft manufacture company. Ohain had a gas turbine engine with a centrifugal air compressor running by September 1937. The first fuel was hydrogen but he switched to gasoline for the HeS 3 engine and this produced a thrust of 1,100 lbf (pound force) or 5 kN (kilo Newtons). Heinkel fitted this into a He 178 airframe that flew on 27 August 27 1939. It was the world's first turbojet-powered aircraft to fly.

György Jendrassik, a Hungarian mechanical engineer, build the world's first turboprop (where the propeller is driven by a gas turbine) but only one was built before the program was cancelled.

In Britain, Frank Whittle received his first patent for a turbo-jet, in 1932 and had an engine running in April 1937. The W1, capable of a thrust of 1000 lbf (4 kN), was installed in a Gloster E28/39 airframe and first flew on 15 May 1941.  Whittle used a centrifugal compressor similar to the centrifugal superchargers commonly used on piston engines. The incoming air was accelerated outward and then compressed in a duct, converting its velocity into pressure. The air flow was reversed through the combustion section and again reversed into the turbine thus reducing efficiency.

Frank Halford, a British aircraft engine designer, developed an axial compressor 'straight through' version of Whittle's centrifugal compressor and this design became the de Havilland Goblin.

The first turbines were not able to spin fast enough to reduce the compressor diameter so they had a large frontal area and more aerodynamic drag. However, they were simple, lightweight and reliable so they could be rapidly developed during wartime.

A cutaway of the Junkers Jumo 004 engine.  Note the muliple rows of compressor fan blades and the single row of gas turbine blades driving the compressor.

Anselm Franz, an Austrian engineer working at Junkers' engine division (Junkers Motoren or Jumo), developed an axial-flow compressor. Air coming in the front of the engine was compressed and forced into the combustion chambers by sets of multi-bladed fans while the burning air/fuel mixture exhausted through the turbine that directly drove the compressor fans. The hot exhaust gas provided the thrust that drove the aircraft. The more complicated compressor made the engine smaller in diameter and thus better suited for high speed aircraft.

Mass production of Jumo 004 engines started in 1944 for the world's first jet-fighter aircraft, the Messerschmitt Me 262, and the world's first jet-bomber aircraft, the Arado Ar 234. 

In Britain, the first axial-flow engine, the Metrovick F.2, was first flown in 1943. It was more powerful than the centrifugal designs but too unreliable so it was improved as the Armstrong Siddeley Sapphire engine which was later built in the USA.

After the war, American, British and Russian engineers studied the German jet engines and adopted many of the features.

Centrifugal compressor were improved with better materials and bearings that allowed higher speeds greatly reducing the diameter of the compressor. Helicopter designers were attracted to the short engine length, lighter weight and lower risk of damage caused by foreign objects.

British gas turbines were made under license in the USA and some were sold to Soviet Russia where they were reverse engineered. The British Nene engine design was thus used to for the MiG-15 jet fighter while the General Electric J47 engine powered F-86 Sabres in the 1950s.

In the 1950s, British designs were approved for civilian use, and were used on the de Havilland Comet and Avro Canada Jetliner. By the 1960s, all large civilian aircraft were jet powered.

Continuous improvements in turboprop design and jet engines and innovations like the high by-pass jet engine made high altitude, long distance travel available at ever decreasing cost.