By 1939, scientists had been conducting laboratory experiments with early jet turbine engines. However, due to the large size and impractical fuel consumption, these machines remained in the laboratory setting. Nevertheless, World War II offered significant financial and military incentives for the advancement of jet engines. In Germany during the War, Hans von Ohain used his jet engine to power Ernst Heinkel’s small aircraft – the Heinkel He178. In late 1939, the flight of this airplane became the first practical use of jet engines. Simultaneously, in England, Sir Frank Whittle was testing his jet engine, the W1. After the Gloster Aircraft Company created their small experimental aircraft, the W1 made its first flight in1941. In history, both Hans von Ohain and Frank Whittle are recognized as the inventors of the jet engine.
Throughout each jet engine, a few components create the primary mechanism of the engine. As air enters through the front of the engine, it passes through a compressor. In this process, the air becomes denser to create greater potential energy. Then, the air is mixed with fuel and explodes in the combustion chamber. Finally, it is directed through a turbine, which is propelled by the extreme velocity of the fuel/air mixture. The first engines of Ohain and Whittle were no exception to these processes. Whittle’s W1 was originally a water-cooled engine weighing 700 pounds and similar to today’s jet fuel, the W1 burned a kerosene-based fuel at a rate of 1,170 lb/hr, while providing 850 lbf. Also during World War I, a German engine designer, Anselm Franz, created a jet engine to be implemented with a military fighter jet. However, after being installed on the Me262, the military realized that due to its size and large fuel consumption, they could not afford to regularly use it in combat.
As Whittle progressed in his development of the engine, he communicated his research and concepts to two engine manufactures: the American based General Electric, and its British counterpart, Rolls Royce. Both of these companies continued the development of the jet engine for the purpose of military aviation. General Electric began with the I-16 engine in 1942, followed by the Allison J33. The latter became the propulsion for the P-80 Shooting Star aircraft.
When World War I came to an end in 1945, the American engine companies of General Electric and Pratt & Whitney gained access to the engine research of Ohain. From this, they further understood the issue of having a high fuel consumption and low thrust. This complication became the primary goal of both companies. In 1948, Pratt & Whitney became the first company to provide a solution. With their J-57 engine, they invented the concept of the dual spool. They implemented two compressors, the first compressed it to the typical pressure and the second compressed it further, creating improved performance. Furthermore, with the higher pressures, they were able to construct two turbines, which provided enough power to drive the two compressors. At the same time, Pratt & Whitney began to incorporate the afterburner into their engines. Contrary to their fuel efficiency goals, the afterburner consists of a chamber at the trailing edge of the engine, which ignites fuel to created increased thrust. With these new technologies, the Pratt & Whitney J-57 created its legacy with the US Air Force F-100, one of the first aircraft to break the sound barrier.
However, in these early stages of the jet engine, there were still more issues that needed investigating. For example, engineers noticed that at certain speeds, the compressor would stall. This occurred because the mechanisms could not function fast enough to use all the intake air. Thus, a blast of air would shoot forward in the engine, causing a complete loss of thrust. This time, General Electric was able to solve the problem, when engineer Gerhard Neumann invented the variable stator. This concept used vanes within the compressor that regulated the airflow through the engine. By controlling the airflow, this idea was able to reduce compressor stalls and improve the efficiency of the engine, by regulating the fuel/air mixture. This invention led to the construction of the General Electric J-79 in 1955. This engine was eventually used with the Lockheed F-104 Starfighter. Costing $1.42 million, this aircraft, with the propulsion of the GE J-79 was able to achieve Mach 2.2. Also around this time, Rolls Royce developed the Olympus. This engine was used to propel the Concorde passenger airliner. The turbojet engine was chosen because of its narrow profile and high performance.
The next step in jet engine technology occurred in 1965 for both General Electric and Pratt & Whitney. With the turbofan, or fanjet, engineers maximized the potential of the exhaust by placing a large turbine near the back of the engine. This final turbine was able to utilize the remaining power of the exhaust. With an additional turbine, engineers were able to add another compressor. However, unlike previous compressors, this new addition acted more like a fan. Placed at the very front of the engine, this fan looks like and behaved similarly to a propeller. With these engines, this fan often provide up to 90 percent of the engine’s total thrust. These engines were primarily developed for large bodied aircraft and resemble the engines that are used with today’s airliners. In the past, engineers focused on increasing thrust and decreasing the weight of the engine. However, with the increase of commercial aviation, engineers saw the need to focus on increasing fuel efficiency with these turbofans. These turbofan engines first went into production with General Electric in 1965. The GE TF-39 was one of the first high-bypass jet engines available. With this, the compressors and turbines consisted of various stages. For instance, a low-pressure compressor may have consisted of six unique stages, creating even high pressures within the engine. This engine was originally used with the Lockheed C-5 in 1968, but it became known in 1969 for its role as the engine of the Boeing 747. However, with this aircraft, fuel efficiency is not ideal. The Boeing 747-400 can carry 63,500 gallons. When carrying 126,000 pounds, the Boeing 747-400 will consume an average of five gallons per mile. Therefore, if the 747-400 only flew a short flight from Minneapolis-St. Paul International Airport to O’Hare International Airport in Chicago, IL, it would fly 335 miles, burning 1,675 gallons of fuel. At the current rate of kerosene-based jet fuel in Minneapolis, MN of approximately $6.00 per gallon, the flight would use $10,050 worth of jet fuel.
From that point, the jet engine structures have remained the same. However, engineers continue to experiment with various metals, different compressor blade spacing/orientation and different number of stages for compressors and turbines. Since 1970, General Electric has developed the GE-90, which adds an additional stage in the high-pressure compressor and uses composite materials for the fan. In 1995, this engine became used as the propulsion for the Boeing 777. Next, in 2000, Rolls Royce created the Trent 900 series, which was a larger engine used for powering the Airbus A380.
Finally, in 2006, General Electric began developing the GEnx engine for use with the Boeing 787 Dreamliner. This engine aims to reduce weight, decrease fuel consumption and increase engine life. Using composite metal and titanium, the leading fan blades are lighter. Also, the internal turbine blades are created with titanium aluminide. To improve fuel efficiency, this engine uses a high-pressure compressor with a 23:1 pressure ratio. Also, this engine uses lower internal temperatures, to improve with the engine cooling.
Today, researchers are looking at the future of jet engines for commercial and military aviation. In the future, engineers with focus on using lighter and cheaper materials, creating quieter engines and reducing the carbon footprint of aviation.
