Design optimization of the suspension unit of the liner in the combustion chamber housing

. The design of the suspension unit of the flame tube in the housing of the annular combustion chamber of a ground-based gas turbine installation of a gas pumping unit is given for placing it in a device for fixing the flame tube in the combustion chamber housing, where automatic clearance selection is required arising between the contacting surfaces of the docking nodes of the combustion chamber and the nozzle apparatus of the turbine, when the combustion chamber is operating as part of the engine. The proposed design of the suspension unit of the flame tube in the annular combustion chamber housing makes it possible to increase the reliability and resource of the combustion chamber and, in general, the entire ground-based gas turbine installation by eliminating the jamming of the split rings in the cups of the suspension units and the misalignment of the pushers relative to the suspension units and split support rings.


Introduction
Currently, aviation gas turbine engines (GTE), which have spent their flight life, are widely used to drive gas pumping units (GTU), electric generators, gas jet installations, devices for cleaning quarries, snow plows, etc.The mass use of aircraft engines that have spent their flight life and have retained the ability for further use allows us to preserve the labor embodied in engines (and in general in high-tech products) and save expensive materials used in their creation, as well as achieve economic growth [1][2].
In the article, the possibility of using converted aircraft engines on ground-based power plants will be investigated by the example of the gas turbine engine (largely determining the weight, the possibility of obtaining high operating parameters, the resource and safety of engine operation.The destruction of the main parts of the turbine, both in flight and at gas pumping stations, leads, as a rule, to significant destruction inside the power plant.Therefore, the problem of accurately predicting the durability of the main parts of the turbine, minimizing the probability of destruction, has always been and remains relevant at all stages of the creation, refinement and operation of engines) -serial single-circuit twoshaft gas turbine ground engines NK-16ST and NK-16-18ST for the GTU, developed after the aircraft engines have worked out the resource in flight operation and based on the conversion of aircraft engines of the NK-8-2U family designed by N.D.Kuznetsov.The experience of creating drive units based on an aircraft engine shows that up to about 75% of the components and parts of the base engine can be preserved [1][2].Changes are carried out in the nodes associated with the new purpose of the product, the change of the type of fuel used and the appearance of a power turbine in the converted engine.The power turbine is being created anew (Figure 1 shows the engines and sections of the NK-8-2U engines, as well as NK-16ST and NK-16-18ST).Modern trends in the development of gas turbine engines and ground-based installations, including convertible aircraft engines, determine the development of a heat engine with moderate and high parameters of the thermodynamic cycle, high reliability, large resource combined with operational manufacturability and low cost.Simplicity, reliability, decades-old proven technology of design, manufacture and operation, singlecircuit fuel supply system and unambiguous control in the main modes make justified numerous attempts by designers to improve traditional combustion chambers in order to improve their environmental characteristics, reliability, and resource [3].
To create the most economical and efficient machines, optimization of all major processes and nodes is required.The combustion chamber of a gas turbine engine is one of its main elements, and largely determines the overall environmental characteristics, resource and efficiency of the engine.
Despite the relative simplicity of the design, complex processes occur in the combustion chamber that are difficult to predict and calculate.Currently, traditional design methods are already becoming insufficient, so in recent years various methods of computer-aided design and fine-tuning of engines and their components have been widely used [4].
The suspension unit of the liner in the annular combustion chamber housing is designed to be installed in a device for fixing the flame tubein the annular combustion chamber housing, where automatic clearance selection is required arising between the contacting surfaces of the docking nodes of the combustion chamber and the nozzle apparatus of the turbine.
There are known devices where the nozzle apparatus of a high-pressure turbine is mechanically connected to the rear end of the combustion chamber and forms a single node with it [5,6].
The main disadvantage of these devices is the complexity of their manufacture, and the cantilever suspension of the front part of the flame tube when working as part of the engine can lead to wear of the parts of the burners in contact with the flame tube.
A device is known for fixing a flame tube in the combustion chamber, containing a pin mount on the flanges of the housing in front of the chamber, and at the junction with the turbine -an annular suspension of the ends of the shells of the flame tubeon the annular projections of the turbine stator.The annular protrusions of the outer and inner shells of the flame tubeare supported by split (support) rings equipped with annular protrusions with inclined walls resting on the bevels of the pushers of the suspension units of the flame tube mounted on the camera body and the inner shell.The housing of the suspension units of the flame tube is made in the form of a cup, in the cavity of which the pushers are supported by spherical surfaces on split rings, spring-loaded with a package of disc springs with an adjustment ring between them.There must be at least three suspension units for each shell [7,8].
The main disadvantage of the device is the jamming of the split rings in the cups of the suspension unit due to the load of the disc springs on the split rings.When assembled under the influence of this load, the split rings increase in size in diameter and jam in the cup.During the operation of the combustion chamber in the engine, under the action of thermal linear expansion of the shells of the flame tube, the split support rings move towards the turbine, which, due to the presence of spherical surfaces on the pushers, leads to their skewing relative to the suspension units and the inclined walls of the support split rings.The misalignment of the pushers leads to a decrease in the contact area of the working surfaces between the annular inclined walls of the split support rings and the bevels of the pushers, which, in turn, causes intensive wear of the inclined walls of the split support rings and the bevels of the pushers at the place of their contact.Due to the fact that the split rings in the cups are jammed and the pushers with disc springs are not able to compress the split support rings, then, due to the appearance of gaps, avalanche-like wear of the contact surfaces of the annular protrusions of the shells of the flame tube and the details of the pin connection of the attachment of the flame tube to the camera body in the front part occurs, which dramatically reduces the reliability and service life of the camera, even within the warranty resource.
The purpose of optimizing the design of the suspension unit of the flame tube of the annular combustion chamber is to increase the reliability and resource of the combustion chamber by eliminating the jamming of the split rings in the cups of the suspension units and the misalignment of the pushers relative to the suspension units and split support rings.
The improvement of the design of the suspension unit of the flame tube of the annular combustion chamber is achieved by the fact that the device for fixing the flame tube in the annular combustion chamber uses a pin mount on the flanges of the housing in front of the chamber, and at the junction with the turbine -an annular suspension of the ends of the shells of the flame tube on the annular protrusions of the turbine stator.The annular protrusions of the outer and inner shells of the flame tube are supported by split support rings equipped with annular protrusions with inclined walls resting on the bevels of the pushers of the suspension units of the flame tube mounted on the camera body and the inner shell.The body of the suspension units is made in the form of a cup with pushers placed in it with a package of disc springs and an adjustment ring.To avoid jamming of the pushers in the cups of the suspension unit, the pushers with bevels are made according to a twosupport scheme in the form of a piston with a cylindrical rod and anti-friction coating of all surfaces in contact with adjacent parts.The body of the suspension unit, made in the form E3S Web of Conferences 431, 02020 (2023) ITSE-2023 https://doi.org/10.1051/e3sconf/202343102020 of a cup, contains an additional cylinder for placing a cylindrical rod in it.At the same time, a package of disc springs with an adjustment washer is installed in such a way that it rests on the bottom of the suspension unit body on the one hand, and on the other -on the end surface of the piston.
The absence of split rings, spring-loaded with a package of disc springs, eliminates jamming of them and the pusher in the bodies of the suspension unit, and the two-support design of the pusher eliminates the distortion of the pushers and wear of the contacting surfaces of the suspension parts.Figure 2 shows a general view of the device of the suspension unit of the flame tube in the housing of the annular combustion chamber.The suspension unit contains (Figure 3) a housing 1 with an additional cylinder 2, an annular protrusion 3 of the shell of the flame tube 4, supported by a split support ring 5 with annular inclined walls 6, which, in turn, are supported by the bevels 10 of the pushers 7, made at the same time as a whole the form of a piston 8 with a cylindrical rod 9, and a package of disc springs 11 with an adjustment washer 12 rests on one side in the bottom of the body of the suspension unit 1, on the other -in the end surface of the piston 8.To reduce wear, all the surfaces of the pushers are covered with an anti-friction material, for example, copper.The suspension unit works as follows.After centering the nozzle apparatus with the combustion chamber housing, a split support ring 5 is installed on the annular protrusion 3 of the flame tube 4. Then the suspension units are assembled by placing pushers 7 in the housings 1 with additional cylinders 2, made in the form of a piston 8 with cylindrical rods 9.Between the bottom of the body 1 of the suspension unit and the end surface of the pistons 8, packages of disc springs 11 with adjustment rings 12 are installed to ensure the specified gaps in the free state (not pressed) to the camera body within the tolerance The bodies of the suspension unit 1 are mounted on the flanges of the combustion chamber housing and they are pressed against the chamber housing with bolts 13.The two-support design of the pusher eliminates its misalignment relative to the body 1 of the suspension assembly and the split support ring 5, which, regardless of the operation of the engine, ensures constant uniform compression of the split support ring 5 by the pushers 7.At the same time, a constant contact area is provided for the inclined walls 6 of the removable locking ring 5 and the bevels 10 of the pushers 7. Considering that all the surfaces of the pushers are additionally coated with an antifriction material, for example, copper, this device reduces the wear of the contacting surfaces, increases the reliability and service life of the combustion chamber.

Conclusions
The proposed design of the suspension of the flame tube in the body of the annular chamber has been tested by long-term operation of the NK-16ST and NK-16-18ST engines and confirms the stated advantages.The novelty of the design is confirmed by a patent of the Russian Federation.The described changes in the design, as well as some other measures to clarify the resource of the main parts of the gas turbine engine, made it possible to significantly increase the assigned resource of the NK-16ST and NK-16-18ST engines from 150,000 hours to almost 200,000 hours.

Fig. 2 .
Fig. 2. General view of the suspension unit of the annular combustion chamber flame tube

Fig. 3 .
Fig. 3.The device of the suspension unit of the flame tube of the annular combustion chamber