Description of the D-18T engine

The D-18T was developed by the Ukrainian company Sich, Zaporozhye Motor Sich was founded in 1907 and acquired a big knowledge about the creation of motor's plane. The D-18T three-shaft bypass engine is intended for powering transport planes. The engine features high bypass ratio, three-spool design including axial 15-stage compressor, intermediate casing, annular combustion chamber, 6-stage turbine, thrust reverser inside bypass (fan) duct and separated fixed-area exit nozzles of bypass and main ducts.

The peculiar feature of the three-spool design is that the compressor consists of three independent rotors, every one of them being driven by its own turbine. The rotors have different optimized rotational speeds and have the gas-dynamic relation only. The engine rotary part is supported by six bearings, any of three rotors rides on two bearings.

The engine design is based on modular assembly principle.

The engine consists of 17 main modules and 4 sub-modules, each of them is essentially a complete structurally-technological assembly and can be (except for the master module) removed and replaced in service.

Details of the engine

Compressor

Engine compressor is an axial three-spool assembly consisting of supersonic fan (1), transonic intermediate pressure compressor (2) and subsonic high-pressure compressor (3).

Single stage

Single stage fan consists of the fan rotor wheel, fan casing, straightener vanes, fan shaft with bearing and rotating spinner.

Caption:
1-Fan casing; 2-Protecting ring; 3-Noise suppression panel; 4-Fan rotor wheel; 5-Anti-vibration platform; 6-IPC fairing; 7-Straightener Vane; 8-Spinner; 9-Shaft; 10-Ball bearing.

Intermediate pressure compressor (IPC)

Intermediate Pressure Compressor (IPC) is of the seven-stage design, comprises the front casing, stator and rotor. The front casing fairing separates the air flow downstream of the fan rotor wheel and IPC. The guide vanes and shroud rings of all stages together with casing from stator section of IPC. The frame with removable noise suppression panels form the internal surface of the engine bypass duct in the IPC area. The IPC casing and frame with noise panels make a part of the engine master modules while the IPC st.7 guide vanes assembly makes a part of the intermediate casing from the point of view of providing the engine modular design.

Caption:
1-IPC Front Casing; 2-IPC air bleed valve; 3-Fan guide vanes; 4-Intermediate Casing; 5-IPC Variable inlet guide vanes; 6-IPC st.7 guide vanes assembly; 7-Stator; 8-IPC rotor front bearing; 9-Rotor.

The IPC air bleed valves and variable stator vane are devices anti-pumping. When the engine accelerate, it needs breathing. But due to their inertia, the fan wheel and the compressor don't give it enough air and its temperature increase. So we open the Variable Stator Vane in pointing them in the air flow. In the mean time we close the variable bleed valves.
In the opposite when the engine slow down, the same inertia gives it too much air and an extinction can occur, so we close the variable stator vanes in pointing them perpendicular to the flow and we open the variable bleed valves to drain off the surplus of air.

IPC rotor

IPC rotor is of a drum-and-disk design. The welded drums of st 1 thru 4, st.6 and 7 and st.5 rotor wheel are bolted to front and rear shafts and to each other. The rotor blades are secured in the disk rim by means of dovetails attachment. The IPC rotor is spline-connected to the intermediate pressure turbine rotor. As a unit these assemblies form the intermediate pressure rotor. The IP rotor is installed in two bearing assemblies fitted with the oil dampers. Besides, the IPC front ball bearing is installed in the resilient squirrel-cage support with a rigid travel constraint.

Caption:
1-St.5 rotor wheel; 2-St.6 thru 7 rotor section; 3-St.6 thru 7 rotor section; 4-Front casing; 5-Bearing housing; 6-Jet; 7-Ball bearing; 8-Front shaft; 9-Air bleeding pipe; 10-Rear shaft.

High pressure compressor

High pressure compressor (HPC) is a seven-stage assembly consisting of the inlet guide vanes assembly, rotor, stator, casing and air bleed valves. The HPC rotor is of a drum-and-disk design. The welded drum of st 1 thru 4, st.5 thru 7 disks, spacers and shafts are interconnected by bolts. The rotor blades are secured in the disk rim by means of dovetail attachment. The HPC rotor is bolted to the high pressure turbine rotor. As a unit these assemblies form the high pressure rotor. The HP rotor is installed in two bearing assemblies fitted with the oil dampers. Besides, the HPC front ball bearing is installed in the resilient squirrel-cage support with a rigid travel constraint.

Caption:
1-St.1 thru st.4 rotor section; 2-St5 thru st7 rotor wheels; 3-HPC variable inlet guide vanes; 4-Ball bearing; 5-HPC rear shaft; 6-Jet.

Intermediate casing

Intermediate casing is located between the intermediate pressure compressor and high pressure compressor to form the bypass duct flow section, it serves to secure some engine accessories and accessory drives as well as the high pressure compressor rotor front bearing and engine forward mount.

The intermediate casing consists of the following basic assemblies:

• Intermediate casing proper
• Accessory drive gear box and intermediate drive
• Centrifugal breather drive
• Internal drive

The outer ring of the fan straightener vanes assembly is attached to the front flange of the intermediate casing external shell while the engine thrust reverser is attached to the rear flange.

Combustion chamber

Combustion chamber comprises the casing with two shells to pass air in-between for cooling the IPT elements, air intake diffuser with the HPC st.7 outlet guide vanes, annular flame tube, fuel manifold, fuel nozzles and start igniters.

Caption:
1-Fuel manifold; 2-Fuel nozzle; 3-Igniter; 4-Casing; 5-Dilution air hole; 6-Main air hole; 7-HPT nozzle guide vanes assembly; 8-HPC rotor wheel; 9-Diffuser; 10-HPC outlet guide vanes assembly.

Turbine

Turbine is a three-shaft reaction-type assembly consisting of high-pressure turbine (HPT), intermediate pressure turbine (IPT) and fan turbine (FT). The single-stage HPT and IPT rotors drive the HPC and IPC rotors accordingly while the four-stage FT drives the fan rotor.

Caption:
1-HPT roller bearing (high pressure rotor rear bearing); 2-IPT roller bearing (Intermediate pressure rotor rear bearing); 3-FT roller bearing (fan turbine rotor rear bearing); 4-Fan shaft.

High-pressure turbine

High pressure turbine (HPT) comprises the nozzle guide vanes and rotor wheel. The nozzle guide vanes assembly consists of the separate segments. The vanes are connected by brazing within the same segment. The NGVs are hollow and air-cooled. The HPT rotor blades are also air-cooled. Each slot of the disk accommodates 2 blades. The blades are attached to the disk by means of fir-tree roots.

Caption:
1-Nozzles guide vanes assembly; 2-HPT stator; 3-HPT rotor.

Intermediate pressure turbine

Intermediate pressure turbine (IPT) comprises the bearing housing and rotor wheel. The bearings housing accommodates the rear bearings of the HP and IP rotors. The IPT disk, IPT nozzle guide vanes and rotor blades are cooled. The IPT rotor blades are attached to the disk through fir-tree roots.

Caption:
1-IPT stator; 2-IPT rotor.

Fan turbine

Fan turbine (FT) comprises the rotor and the stator. The fan turbine stator consists of a casing and four NGVs assembled of separate cast segments.

Caption:
1-FT stator; 2-FT rotor.

Fan turbine rotor

FT rotor is of the drum-and-disk design. The disks are connected to each other using spacers and FT rotor shaft by means of bolts. Neither FT NGVs nor rotor blades are cooled. The rotor blades of all FT stages are shrouded.

Caption:
1-Rotor wheel; 2-Labyrinth seal ring; 3-Sealing ring; 4-Roller bearing; 5-Shaft; 6-Radial-face contact seal.

Turbine exhaust

Turbine exhaust unit consist of the rear bearing and main duct jet nozzle. The rear bearing accommodates the fan rotor roller bearing.

Caption:
1-Jet nozzle; 2-Heat insulation material; 3-Exhaust cone.

D-18T Séries 4

D-18T, series 4, engine also differs from D-18T, series 3, engine due to installation of the noise-suppression structures, updating the engine control system and engine thrust reverser control system.
In red the differences between series 3 and 4.

Caption:
1-Fan wheel; 2-IPT NGVs; 3-Nozzle guide vanes and rotor blades; 4-Fan turbine blades and NGVs; 5-Fan turbine st.3 disk; 6-Main duct nozzle.

System

Engine thrust reverser is of an annular lattice assembly with flaps closing the engine bypass duct flow area during thrust reversing.

Fuel system provides for the duel supply to the engine in quantity determined by the position of the throttle control lever and the flight conditions. The fuel system permits to use either domestic grades of fuel (PT, TC-1) or foreign grades (Jet A-1 DERD 2494, Jet-A ASTM 1655)

Engine starting is performed automatically. The acceleration of hight-pressure rotor is effected by the air turbine starter installed on the accessories drive gear box. The plane-mounted auxiliary gas-turbine engine, ground air source as well as another operative propulsion engine can be used as compressed air supply for acceleration of the air turbine starter.