Different Types of Combustion Chamber and Turbine

Different types of combustion chamber and turbine TYPES OF COMBUSTIO C!"MBE# Mu$tip$e combustion chambers %Mu$tip$e can&type combustion chamber' This type of combustion chamber is used used on centri centrifug fugal al compr compress essor or type type engines. It has several cans disposed arou round the the engin gine. Each can is a complete

combustion

chamber 

consis consistin ting g of its own air outer outer with with a flame-tu flame-tube be

(or burner burner liner) liner) inside. inside.

Compressor delivery air is directed by ducts to pass into the individual chambers. Each can contain its own fuel nozzle. The chamber cans are all interconnected. This allows each can to operate at the same pressure and also allows combustion to propagate around the flame tubes during engine starting. Igniter plugs are installed on two of the cans approimately at ! and " #$cloc% positions.

Turbo&annu$ar Turbo&annu$ar combustion chamber %Can&annu$ar '

 &

Turbo-

annular  combustion chamber  design used

is on

many

large

turbo'et and turbofan engines. Individual burner cans are placed side by side to form a circle of cans inside an annular space between outer  and inner air casings. The cans are essentially individual combustion chambers with concentric rings of perforated holes to admit air for cooling.

"nnu$ar combustion chamber  ome aial compressor engines have a single annular combustion chamber. This type of combustion chamber consists of a single flame

tube (i.e. liner) completely

annular in form which is contained in the annulus of an inner and outer casing. The chamber

is

open

at

the

front

to

the

compressor and at the rear to the turbine nozzles. *owever the burner liner on some engines cannot be disassembled without removing the engine from the aircraft which is a distinct disadvantage.

Operation Mu$tip$e combustion chambers %Mu$tip$e can&type combustion chamber'

The chambers are disposed around the engine and compressor delivery air is directed by ducts to pass into the individual chambers. Each chamber has an inner flame tube around which there is an air casing. The air passes through the flame tube snout and also between the tube and the outer casing.

Turbo&annu$ar combustion chamber %Can&annu$ar ' #n some engine models each can is provided with a round perforated tube which runs down the middle of the can. The tube carries additional air which enters the can through the perforations to provide more air for combustion and cooling. The effect is to permit more burning per inch of can length than could otherwise be accomplished. everal fuel nozzles are placed around the perimeter of the forward end of the can. Instead of individual combustion chambers the compressed air is introduced into an annular space formed by a combustion chamber liner around the turbine shaft. +sually enough space is left between the outer liner wall and the combustion chamber housing to permit the flow of cooling air from the compressor. ,uel is introduced through nozzles or in'ectors connected to a fuel manifold. The nozzle opening may face upstream or downstream to airflow depending on engine design. arious means are provided to introduce primary (compressed) air  to the vicinity of the nozzle or in'ectors to support combustion and additional air downstream to increase the mass flow. econdary cooling air reduces the temperature of gases entering the turbine to the proper level.

"nnu$ar combustion chamber  The liner of this type of combustion chamber consists of continuous circular inner and outer shrouds. *oles in the shrouds allow secondary cooling air to enter the center of the combustion chamber %eeping the flame away from the shrouds. In the annular combustion chamber fuel is introduced through a series of nozzles at the upstream end of the liner. ecause of their proimity to the flames all types of burner liners are short-lived in comparison with other engine components re/uiring more fre/uent inspection and replacement. This type of  combustor has the advantage of being able to use the limited space available most effectively permitting better miing of the fuel and air within a relatively simple structure.

M"TE#I"(S "D COTS#UCTIO

Mu$tip$e combustion chambers

Each can-type combustion chamber consists of an outer case or housing with a perforated stainless steel (highly heat-resistant) combustion chamber liner or inner liner. The outer case is divided for ease of liner replacement. The larger section or chamber body encases the liner at the eit end0 the smaller chamber cover encases the front or inlet end of the liner. The interconnector (flame propagation) tubes are a necessary part of can-type combustion chambers. ince each can is a separate burner operating independently of the others there must be some way to spread combustion during the initial starting operation. This is done by interconnecting all the chambers. The flame is started by the spar% igniter plugs in two of the lower chambers0 it passes through the tubes and ignites the combustible miture in the ad'acent chamber. This continues until all chambers are burning. The flame tubes will vary in construction details from one engine to another although the basic components are almost identical. The interconnector tubes are shown in the figure above. ear in mind that not only must the chambers be interconnected by an outer tube (in this case a ferrule) but there must also be a slightly longer tube inside the outer one to interconnect the chamber liners where the flame is located The outer tubes or 'ac%ets around the interconnecting flame tubes not only afford airflow between the chambers but also fulfill an insulating function around the hot flame tubes. The spar% igniters are normally two in number. They are located in two of the can-type combustion chambers. ¬her very important re/uirement in the construction of combustion chambers is providing the means for draining unburned fuel. This drainage prevents gum deposits in the fuel manifold nozzles and combustion chambers. These deposits are caused by the residue left when fuel evaporates. If fuel is allowed to accumulate after shutdown there is the danger of after 

fire. If the fuel is not drained a great possibility eists that at the net starting attempt ecess fuel in the combustion chamber will ignite and tailpipe temperature will go beyond safe operating limits. The liners of can-type combustors have perforations of various sizes and shapes each hole having a specific purpose and effect on flame propagation in the liner. &ir entering the combustion chamber is divided by holes louvers and slots into two main streams 1 primary and secondary air. 2rimary (combustion) air is directed inside the liner at the front end where it mies with the fuel and bums. econdary (cooling) air passes between the outer casing and the liner and 'oins the combustion gases through larger holes toward the rear of the liner cooling the combustion gases from about 3"445 , to near 6"445 ,. *oles around the fuel nozzle in the dome or inlet end of the can-type combustor liner aid in atomization of the fuel. 7ouvers are also provided along the aial length of the liners to direct a cooling layer of air along the inside wall of  the liner. This layer of air also tends to control the flame pattern by %eeping it centered in the liner preventing burning of the liner walls. Turbo&annu$ar combustion chamber  %Can&annu$ar' The split compressor re/uires two concentric shafts to 'oin the turbine stages to their respective compressors. The front compressor 'oined to the rear turbine stages re/uires the longer shaft. ecause this shaft is inside the other a limitation is imposed on diameter. The distance between the front compressor and the rear turbine must be limited if critical shaft lengths are to be avoided. ince the compressor and turbine are not susceptible to appreciable shortening the necessary shaft length limitation had to be absorbed by developing a new type of  burner. & design was needed that would give the desired performance in much less relative distance than had previously been assigned. Can-annular combustion chambers are arranged radially around the ais of the engine in this instance the rotor shaft housing. The combustion chambers are enclosed in a removable steel shroud that covers the entire burner section. This feature ma%es the burners readily available for any re/uired maintenance. The burners are interconnected by pro'ecting flame tubes. These tubes ma%e the engine-starting process easier. They function identically with those previously discussed but differ in construction details. Each combustion chamber contains a central bullet-shaped perforated liner. The size and shape of the holes are designed to admit the correct /uantity of air at the correct velocity and angle. Cutouts are provided in two of the bottom chambers for installation of the spar% igniters. The combustion chambers are supported at the aft end by outlet duct clamps. These clamps secure them to the turbine nozzle assembly.

"nnu$ar combustion chamber  ome provision is always made in the combustion chamber case or in the compressor air outlet elbow for installation of a fuel nozzle. The fuel nozzle delivers the fuel into the liner in a freely atomized spray. The freer the spray the more rapid and efficient the burning process. Two types of fuel nozzles currently being used in the various types of combustion chambers are the simple nozzle and the duple nozzle. The annular combustion chamber consists basically of a housing and a liner as does the can type. The liner consists of an undivided circular shroud etending all the way around the outside of the turbine shaft housing. The chamber may be constructed of one or more bas%ets. If two or more chambers are used one is placed outside the other in the same radial plane0 hence the term 8double-annular chamber.8 The spar% igniter plugs of the annular combustion chamber are the same basic type used in the can combustion chambers although construction details may vary. There are usually two plugs mounted on the boss provided on each of the chamber housings. The plugs must be long enough to protrude from the housing into the outer annulus of the double-annular combustion chamber.

"D)"T"*E "D DIS"D)"T"*ES

"D)"T"*E

9ultiple combustion chambers

(9ultiple can-type combustion chamber)

DIS"D)"T"*E

Its main advantage is easy

 &s a disadvantage the

replacement of the individual

combustion is inefficient and

burner cans.

combustor is structurally wea%er that other forms of combustors.

"nnu$ar combustion chamber 

It has several advantages as it is

+nfortunately repairs or

the most efficient and strongest

replacement will necessitate a

as it forms frame member of

whole engine disassembly0

engine

thereby time consuming and epensive.

Turbo-annular combustion chamber (Can-&nnular)

 &s such the combustor is strong

+nfortunately it is less efficient

and is easy to conduct

than the annular combustor 

replacement and repair 

TYPES OF *"S TU#BIE E*IE COMP#ESSO# Centrifu+a$ The idealized compressive dynamic turbo-machine achieves a pressure rise by adding %inetic energy:velocity to a continuous flow of fluid through the rotor or impeller. This %inetic energy is then converted to an increase in  potential energy:static pressure by slowing the flow through a diffuser. The pressure rise in impeller is in most cases almost e/ual to the rise in the diffuser section. ",ia$ turbines

 &n aial turbine operates in the reverse of an aial compressor. & set of static guide vanes or nozzle vanes accelerates and adds swirl to the fluid and directs it to the net row of turbine blades mounted on a turbine rotor.

OPE#"TIO Centrifu+a$ The fluid enters the center of the chamber where it is sent through the rotary movement of the wheel. This motion forces the fluid towards the eterior part of the chamber. Conse/uently the fluid enters the diffuser which converts the energy created by the spinning motion into pressure that throws such fluids outwards at high momentum. &s such the e'ected fluid eerts high pressure on the aircraft$s body resulting in a forward thrust. ",ia$  &ial turbines are comprised of a series of propellers or blades that run along a shaft and are set such that they are alternately static or rotating during operation. *owever the aial turbine delivers lesser pressures and speeds when compared to the centrifugal turbines. In that sense the aial turbines usually create pressure in a progressive manner. 2ressure and velocity changes during this phase the pressure and temperature of the gases decreases resulting in increased volume. Conse/uently the velocity of the epanding gases will increase during the epansion process. Components and purpose the turbine is an arrangement of blades on a dis% which rotates due to impingement of fluid. & turbine produces tor/ue as a result of a momentum change of the fluid as it flows the curved surface of the blades.

M"TE#I"(S "D COTS#UCTIO Centrifu+a$ The centrifugal-flow compressor basically consists of an impeller (rotor) a diffuser  (stator) and a compressor manifold. The impeller and the diffuser are the two main functional elements. <hough the diffuser is a separate component positioned inside and secured to the manifold the entire assembly (diffuser and manifold) is often referred to as the diffuser. The principal differences between the two types of impellers are size and ducting arrangement. The double-entry type has a smaller diameter but is usually operated at a higher 

rotational speed to ensure enough airflow. The single-entry impeller permits convenient ducting directly to the impeller eye (inducer vanes) as opposed to the more complicated ducting necessary to reach the rear side of the double-entry type. <hough slightly more efficient in receiving air the single-entry impeller must be large in diameter to deliver the same /uantity of  air as the double-entry type. This of course increases the overall diameter of the engine. Included in the ducting for double-entry compressor engines is the plenum chamber. This chamber is necessary for a double-entry compressor because air must enter the engine at almost right angles to the engine ais. To give a positive flow air must surround the engine compressor at a positive pressure before entering the compressor. 9ultistage centrifugal compressors consist of two or more single compressors mounted in tandem on the same shaft. The air compressed in the first stage passes to the second stage at its point of entry near the hub. This stage will further compress the air and pass it to the net stage if there is one. The problem with this type of compression is in turning the air as it is passed from one stage to the net. ",ia$  &ial-flow compressors have two main elements; a rotor (drum or disc type) and a stator. These compressors are constructed of several different materials depending on the load and operating temperature. The drum-type rotor consists of rings that are flanged to fit one against the other so that the entire assembly can be held together by through bolts. This type of  construction is satisfactory for low-speed compressors where centrifugal stresses are low (,igure-3-otor blades are generally machined from stainless steel forgings although some may be made of titanium in the forward (colder) section of the compressor (,igure 3-?). The blades are attached in the disc rim by different methods using either the fir-tree-type dovetail-type or bulbtype root designs. The blades are then loc%ed into place with screws peening loc%ing wires pins %eys or plates (,igure 3-@). The blades do not have to fit too tightly in the disc because centrifugal force during engine operation causes them to seat. &llowing the blades some movement reduces the vibrational stresses produced by high-velocity airstreams between the blades. The newest advance in technology is a one-piece design machined blade disc (combined disc and blade)0 both disc and rotor blade are forged and then machined into one (refer to ,igure 3-? again).

Clearances between rotor blades and the outer case are very important to maintain high efficiency. ecause of this some manufacturers use a 8wear fit8 design between the blade and outer case. ome companies design blades with %nife-edge tips that wear away to form their  own clearances as they epand from the heat generated by air compression. #ther companies coat the inner surface of the compressor case with a soft material (Teflon) that can be worn away without damaging the blade. >otor discs that are 'oined together by tie bolts use serration splines or curve coupling teeth to prevent the discs from turning in relation to each other.  ¬her method of 'oining rotor discs is at their rims.  &ial-flow compressor casings not only support stator vanes and provide the outer wall of  the aial paths the air follows but also provide the means for etracting compressor air for  various purposes. The stator and compressor cases show great differences in design and construction. ome compressor cases have variable stator vanes as an additional feature.

#thers (compressor cases) have fied stators. tator vanes may be either solid or hollow and mayor may not be connected at their tips by a shroud. The shroud serves two purposes. ,irst it provides support for the longer stator vanes located in the forward stages of the compressor  second it provides the absolutely necessary air seal between rotating and stationary parts. ome manufacturers use split compressor cases while others favor a weldment which forms a continuous case. The advantage of the split case is that the compressor and stator blades are readily available for inspection or maintenance. #n the other hand the continuous case offers simplicity and strength since it re/uires no vertical or horizontal parting surface. oth the case and the rotor are very highly stressed parts. ince the compressor turns at very high speeds the discs must be able to withstand very high centrifugal forces. In addition the blades must resist bending loads and high temperatures. Ahen the compressor is constructed each stage is balanced as a unit. The compressor case in most instances is one of the principal structural load-bearing members of the engine. It may be constructed of aluminum steel or  magnesium.

"D)"T"*E "D DIS"D)"T"*ES

"D)"T"*E

•

*igh pressure rise per stage.

•

Efficiency over wide rotational speed range.

Centrifu+a$

DIS"D)"T"*E

•

7arge frontal area for given airflow.

•

Impracticality if more

implicity of manufacture with

than two stages

resulting low cost.

because of losses in

•

7ow weight.

turns between stages.

•

7ow starting power re/uirements.

•

•

*igh pea% efficiency.

•

mall frontal area forgiven airflow.

•

",ia$

•

•

traight-through flow allowing high ram efficiency. Increased pressure rise due to increased number of stages with negligible losses.

•

•

•

Bood efficiency over narrow rotational speed range. =ifficulty of manufacture and high cost. >elatively high weight. *igh starting power re/uirements (this has been partially overcome by split compressors).