1.2. Design features of manifold types of gas turbine engines

Gas turbine engines can be of different designs. They differ both in relative position of the main engine units and accessories arrangement, that is layout, and units design. Generally, the GTE design of manifold types is selected taking into account the designation and requirements made of the engine.

Table 1.3

Main specifications for some serial turboprop and turboshaft

engines used in civil aviation

Engine	Country	Takeoff rating power N, kW	Efficient fuel con-sumption Ce, kg/(kWh)	Com-pressor pres-sure ratio *c	Mass air flow rate Ga, kg/s	Turbine inlet tempe-rature Т*ti, К	Mass of engine Meng, kg
ТГД-10	USSR	736,0	0,340	7,4	4,1	1270	225
ТГД-20	USSR	1100,0	0,330	9,5	5,9	1270	360
АИ-24Т	USSR	2075,0	0,340	7,7	14,4	1200	600
АИ-20М	USSR	3200,0	0,330	8,5	21,0	1200	1000
НК-12МВ	USSR	11000,0	0,280	9,7	49,5	1200	2950
ГТД-350	USSR	258,0	0,480	6,0	2,5	1228	175
ТВ2-117А	USSR	1100,0	0,360	6,6	8,2	1150	330
ТВ3-117	USSR	1840,0	0,340	8,5	9,2	1300	300
Д-136	USSR	8700,0	0,300	17,5	55,0	1400	1000
GT7-5	England	912,0	0,330	7,5	5,5	1370	307
PT-7A	Canada	1026,0	0,360	9,0	6,5	1250	500
T55L-9	USA	1860,0	0,376	6,4	9,7	1400	620
T56A-7	USA	2980,0	0,330	9,5	15,0	1243	846
T53L-13	USA	1130,0	0,357	7,4	5,8	1200	240
T55L-5	USA	1620,0	0,358	6,3	8,7	1250	258
T-700-68	USA	1147,0	0,307	17,0	4,5	1473	235

The turbojet engines structurally differ in such characteristic features as: the type of compressor and turbine, the number of rotors, means of thrust augmentation, inlet and exhaust arrangement types.

Single-rotor TJE with subsonic inlet, axial-flow or centrifugal compressor and without afterburner is an engine of an elementary scheme, which is used on aircraft with subsonic flight speeds. The inlet of such engines functions as a channel, that supplies air to the compressor without considerable transformation of air kinetic energy into pressure potential energy. The compressor can be of axial-flow or centrifugal type depending on the required value of air pressure ratio. The principal scheme of TJE with the axial-flow compressor is shown in Fig. 1.1. and the principal scheme of the TJE with the centrifugal compressor is shown in Fig. 1.2. The combustion chambers are tubular (“can”), annular or cannular (“can”-“annular”). The gas turbine has one or two stages. A nozzle, as a rule, is of a constant geometry. The arrangements of sound suppression and thrust reversing can be placed in an exhaust arrangement. They are used for decreasing an airplane roll-out after landing as well a s for noise abatement.

Fig. 1.1. Principal scheme of TJE with an axial-flow compressor

Fig. 1.2. Principal scheme of TJE with a centrifugal compressor

The augmented ATJE (Fig. 1.3) has an afterburner, located behind the turbine. In the afterburner the additional fuel is burnt to increase engine thrust for a short time. The ATJE nozzle is a variable to provide an augmented turbojet engine afterburning rating, to facilitate the engine starting, and also to increase the engine efficiency and profitability in flight.

Depending on the number of rotors, TJEs are subdivided into single- and two-shaft. Two-shaft ATJE (Fig. 1.3) has two consecutive compressor spools of low and high pressure, which rotate with the help of kinematically independent turbines.

Such layout has a number of important advantages. There is no unstable compressor operation in case engine rating deviates from designed one due to “rotors slip”. Thus, the absence of mechanical connection between rotors permits a more flexible engine control under the optimal laws. It is enough to crank only high pressure rotor for engine starting, and due to this the required starter power and starting time of the engine are reduced. The two-shaft engine is structurally more composite than single-shaft engine because of the greater number of supports, shafts, couplings and more complex lubricating system.