Gas-Turbine Engine

a heat engine in which gas is compressed and heated and the energy of the compressed and heated gas is then converted to mechanical work on the shaft of the turbine. A gas-turbine engine may operate with continuous combustion of the fuel at constant pressure or with intermittent combustion at constant volume.

The idea of building a gas-turbine engine was first proposed in 1791 by the English inventor J. Barber, who proposed using a gas generator, a piston compressor, a combustion chamber, and a gas turbine. In 1892 the Russian engineer P. D. Kuz’minskii designed, and in 1900 built, a gas-turbine engine with fuel combustion at constant pressure; the engine was designed to power a small cutter. A multistage gas turbine was used in this engine. Because of Kuz’minskii’s death, tests of his engine were not completed. Between 1900 and 1904 the German engineer F. Stolze tried to build a gasturbine engine but failed. In 1906 the French engineers R. Armengaud and C. Lemale built a gas-turbine engine that operated on kerosine and burned fuel at a constant pressure; however, its efficiency was low, and it did not find application in industry. The Russian engineer V. V. Karavodin designed in 1906 and built in 1908 a compressorless gas-turbine engine with four intermittent-combustion chambers and a gas turbine whose output reached 1.2 kilowatts (kW), or 1.6 hp, at 10,000 rpm. In 1908 a gas-turbine engine with intermittent combustion was built according to the design of the German engineer H. Holzwarth. By 1933 the efficiency of intermittent-combustion gas-turbine engines was about 24 percent; however, they did not find wide application in industry. In 1909 the Russian engineer N. V. Gerasimov received a patent for the invention of a gas-turbine engine that he used to develop jet thrust (a turbojet gas-turbine engine). In 1913, M. N. Nikol’skoi designed a gas-turbine engine using a three-stage gas turbine to develop 120 kW (160 hp). In 1923, V. I. Bazarov proposed a design for a gas-turbine engine that was similar to the designs of modern turboprop engines. In 1930, V. V. Uvarov, aided by N. R. Briling, designed an engine with a centrifugal compressor, which was constructed in 1936. Major contributions to the creation of aviation gasturbine engines were made in the 1930’s by the Soviet designer A. M. Liul’ka (now an academician of the Academy of Sciences of the USSR), the English inventor F. Whittle, and the German engineer L. Franz. In 1939 a gas-turbine engine with a power of 4,000 kW (5,400 hp) was built and tested in Switzerland. The Slovak scientist A. Stodola was its creator. In Kharkov, in a laboratory headed by V. M. Makovskii, a gas-turbine engine with a power of 736 kW (1,000 hp) was built in 1939. This engine used as fuel the gas produced by underground gasification of coal. Testing of this engine in Gorlovka was cut short by the Great Patriotic War. Among the Soviet scientists and engineers who made major contributions to the development and improvement of gas-turbine engines were A. G. Ivchenko, V. la. Klimov, N. D. Kuznetsov, I. I. Kulagin, T. M. Mel’kumov, A. A. Mikulin, B. S. Stechkin, S. K. Tumanskii, la. I. Shnee, and L. A. Shubenko-Shubin. Among the foreign firms working on gasturbine engines in the 1940’s were Junkers and BMW of Germany, Bristol-Siddeley and Rolls-Royce of Great Britain, General Electric and General Motors of the USA, and Rateau of France.

Gas-turbine engines with continuous combustion of fuel at constant pressure are the type that is most widely used in industry. In this engine (see Figure 1), compressed atmospheric air passes from the compressor to the combustion

Figure 1. Gas-turbine engine: (1) centrifugal compressor, (2) combustion chamber, (3) fuel injector, (4) nozzle, (5) turbine rotor, (6) exhaust pipe

chamber, to which the fuel is supplied. As the fuel burns, it heats the air. The energy of the gaseous products of combustion is then converted to mechanical work in the gas-turbine. A large part of this work is expended in compressing the air in the compressor; the remaining part is transmitted to the unit being driven. It is this work that is the useful work of the engine. The useful work L_e per kilogram of the working component is equal to the difference between the work L_t developed by the turbine during the expansion of the gas in it and the work L_c expended by the compressor for compression of the air in it. The operating cycle of a gas-turbine engine may be plotted on a graph in a PV diagram, where P is pressure and V is volume (see Figure 2). The greater the efficiency of the compressor and the turbine, the lower L_c and the higher L_t, that is, the greater the useful work. An increase in the temperature of the gas before it enters the turbine also facilitates a rise in useful work L’_c (curve 3′4′, Figure 2). The operating efficiency of a gas-turbine engine is described by the ratio of useful work to the amount of heat expended to create the work. In modern gas-turbine engines the efficiency of compressors and turbines is 0.88-0.9 and 0.9-0.92, respectively. The temperature of the gas before it enters the turbine may be 1100°-1200° K in transportation and stationary gas-turbine engines and up to 1600° K in aviation engines. The use of heat-resistant materials in the manufacture of turbine parts and the presence of a cooling system have made possible operation at these temperatures. At the

Figure 2. Operating cycle of a gas-turbine engine in a PV diagram: 1P_nP₂2 is L_c, 4P_nP₂3 is L_t, 4123 is L_e, and 4′123′ is L′_e

present level of advancement of the flow section and a gas temperature of 1000° K, the efficiency of a gas-turbine engine operating according to the simplest design is not higher than 25 percent. To increase efficiency, the heat in the gases leaving the turbine is utilized during the operating cycle to warm the compressed air supplied to the combustion chamber. Heat exchange between the exhaust gases and the compressed air going into the combustion chamber takes place in regenerative heat exchangers. The operating process of the gas-turbine engine during which the heat of the exhaust gases is utilized is called a regenerative process. The efficiency of a gas-turbine engine may also be raised by heating the gas during its expansion in the turbine using the heat of exhaust gases, as well as by cooling the air while it is compressed in the compressor (see Figure 3). In this way useful work increases because of an increase in the work L_m developed by the turbine and a decrease in the work L_c required by the compressor. A design for such a gas-turbine engine was introduced in the 1930’s by the Soviet scientist G. I. Zotikov.

Figure 3. Diagram of a gas-turbine engine with regeneration of heat, cooling of air during compression, and heating of the gas during expansion: (1) starter engine, (2) low-pressure compressor, (3) medium-pressure compressor, (4) high-pressure compressor, (5) combustion chamber, (6) high-pressure turbine, (7) low-pressure turbine, (8) regenerator, (9) air cooler

A compressor and low-pressure turbine are mounted on the same shaft, which is not connected to the drive shaft of, for example, a generator or screw propeller. Their rate of rotation can change depending upon the mode of operation; this significantly improves the efficiency of the engine when not at full power.

Gas-turbine engines may operate on gaseous fuel (natural gas, by-product fuel gases, gas-generator gases, gases from blast and carbon-black furnaces, and gases produced by underground gasification), liquid fuel (kerosine, gas oil, diesel oil, and mazut), and solid fuel (coal and peat dust). Heavy liquid and solid fuels are used in gas-turbine engines operating on a semiclosed or closed cycle (see Figure 4). In closed-cycle engines the working component is not discharged after its work in the turbine has been done; rather, it is used in the next cycle. Such gas-turbine engines allow for an increase in unit power and for the use of nuclear fuel. Gas-turbine engines have found wide application in aviation as the main engines of the power plants in airplanes, helicopters, and drone aircraft. Gas turbines are used to drive generators in steam power plants and in mobile electric power plants—for example, aboard trains. Gas-turbine engines may drive air and gas compressors while simultaneously producing electrical and heat energy; they are used thus in the petroleum, gas, metallurgical, and chemical industries. Gas-turbine engines may be used as the traction motors in gas-turbine locomotives, buses, freight and passenger vehicles, caterpillar tractors, and tanks; as the power plant of ships, cutters and submarines; to drive auxiliary machines and mechanisms such as winches and pumps; and in military installations as sources of energy and as traction power units. The sphere of application of gas-turbine engines has been widening. In 1956 the capacity of all gas-turbine engines in the world exceeded 900 MW; by 1958 it exceeded 2,000 MW, and by early 1968 it reached 40,000 MW (not including aviation and the military). The most powerful gasturbine engine produced in the USSR has a power of 100 MW (1969). The operating efficiency of the engines has reached 35 percent.

Figure 4. Diagram of a gasturbine engine operating on a closed cycle: (1) surface heater, (2) turbine, (3) compressor, (4) cooler, (5) regenerator, (6) air accumulator, (7) auxiliary compressor

The development of gas-turbine engines is proceeding along the path of improvement of their components (the compressor, turbine, combustion chamber, and heat exchangers), increasing the temperature and pressure of the gas before it enters the turbine, and the use of combination power units with steam turbines and free-piston gas generators. The use of such units in stationary power systems and in transportation has shown that when the heat of exhaust gases is utilized and when the basic components are advanced, actual efficiency may reach 42-45 percent.