SGT A ALANKARSGT A ALANKAR

• THE AIR/ FUEL MIXTURE BURNS INSIDE THE AIR/ FUEL MIXTURE BURNS INSIDE

THE COMBUSTION CHAMBER.THE COMBUSTION CHAMBER.

PROPER BURNING MUST TAKE PLACE PROPER BURNING MUST TAKE PLACE DURING ENGINE OPERATION. DURING ENGINE OPERATION.

PROPER STABILIZATION AND PROPAGATION PROPER STABILIZATION AND PROPAGATION OF FLAME IN THE COMBUSTION CHAMBER ARE OF FLAME IN THE COMBUSTION CHAMBER ARE

ESSENTIAL FOR OPTIMUM ENGINE POWER. ESSENTIAL FOR OPTIMUM ENGINE POWER.

THE AMOUNT OF FUEL ADDED TO THE AIR WILL DEPEND THE AMOUNT OF FUEL ADDED TO THE AIR WILL DEPEND UPON THE TEMPERATURE RISE REQUIRED. THE MAXIMUM UPON THE TEMPERATURE RISE REQUIRED. THE MAXIMUM TEMPERATURE IS LIMITED TO 850 TO 1700 degree C BY THE TEMPERATURE IS LIMITED TO 850 TO 1700 degree C BY THE MATERIALS FROM WHICH THE TURBINE BLADES AND MATERIALS FROM WHICH THE TURBINE BLADES AND NOZZLES ARE MADE.NOZZLES ARE MADE.

THE AMOUNT OF FUEL ADDED TO THE AIR WILL DEPEND THE AMOUNT OF FUEL ADDED TO THE AIR WILL DEPEND UPON THE TEMPERATURE RISE REQUIRED. THE MAXIMUM UPON THE TEMPERATURE RISE REQUIRED. THE MAXIMUM TEMPERATURE IS LIMITED TO 850 TO 1700 degree C BY THE TEMPERATURE IS LIMITED TO 850 TO 1700 degree C BY THE MATERIALS FROM WHICH THE TURBINE BLADES AND MATERIALS FROM WHICH THE TURBINE BLADES AND NOZZLES ARE MADE.NOZZLES ARE MADE.

COMBUSTION COMBUSTION CHAMBERSCHAMBERS

JET ENGINES EMPLOY VARIOUS JET ENGINES EMPLOY VARIOUS TYPES OF COMBUSTION TYPES OF COMBUSTION CHAMBERS FOR BURNING OF CHAMBERS FOR BURNING OF AIR/FUEL MIXTURE AND AIR/FUEL MIXTURE AND GENERATING LARGE AMOUNT OF GENERATING LARGE AMOUNT OF HEAT DEPENDING UPON DESIGN HEAT DEPENDING UPON DESIGN REQUIREMENTS.REQUIREMENTS.

COMBUSTION COMBUSTION CHAMBERSCHAMBERS

•TO ENSURE EFFECTIVE AND TO ENSURE EFFECTIVE AND EFFICIENT COMBUSTION OF EFFICIENT COMBUSTION OF AIR/FUEL MIXTURE AND MAINTAIN AIR/FUEL MIXTURE AND MAINTAIN OPTIMUM TEMPERATURES OF THE OPTIMUM TEMPERATURES OF THE COMBUSTION PRODUCTS DURING COMBUSTION PRODUCTS DURING THE ENTIRE RANGE OF ENGINE THE ENTIRE RANGE OF ENGINE OPERATION.OPERATION.

COMBUSTION COMBUSTION CHAMBERSCHAMBERS

VARIOUS DESIGN FEATURES ARE VARIOUS DESIGN FEATURES ARE INCORPORATED IN THE INCORPORATED IN THE COMBUSTION CHAMBERS FROM COMBUSTION CHAMBERS FROM SHAPE, SIZE TO THE MATERIAL SHAPE, SIZE TO THE MATERIAL AND HEAT TREATMENT SO THAT AND HEAT TREATMENT SO THAT THEY MEET THEIR THEY MEET THEIR REQUIREMENTS.REQUIREMENTS.

TYPES OF COMBUSTION CHAMBERTYPES OF COMBUSTION CHAMBER

TYPES OF COMBUSTION CHAMBERSTYPES OF COMBUSTION CHAMBERS

TYPES OF COMBUSTION CHAMBERTYPES OF COMBUSTION CHAMBER

The combustion chamber has the difficult task The combustion chamber has the difficult task of burning large quantities of fuel, supplied of burning large quantities of fuel, supplied through the fuel spray nozzles, with extensive through the fuel spray nozzles, with extensive volumes of air, supplied by the compressor, and volumes of air, supplied by the compressor, and releasing the heat in such a manner that the air is releasing the heat in such a manner that the air is expanded and accelerated to give a smooth expanded and accelerated to give a smooth stream of uniformly heated gas at all conditions stream of uniformly heated gas at all conditions required by the turbine. This task must be required by the turbine. This task must be accomplished with theaccomplished with the minimum loss in pressure minimum loss in pressure and with the maximum heat release for the limited and with the maximum heat release for the limited space available. Hence, the combustion chamber space available. Hence, the combustion chamber have certain have certain design and operational requirementsdesign and operational requirements..

1.1. Since the gas temperature required at the turbine Since the gas temperature required at the turbine varies with engine thrust, and in the case of the varies with engine thrust, and in the case of the turbo-propeller engine upon the power required,turbo-propeller engine upon the power required,

the combustion chamber must be the combustion chamber must be capable of maintaining stable and capable of maintaining stable and efficient combustion over a wide efficient combustion over a wide range of engine operating range of engine operating conditions.conditions.

2. 2. High combustion efficiencyHigh combustion efficiency has become increasingly important has become increasingly important

because of the rapid rise in commercial because of the rapid rise in commercial aircraft traffic and the consequent aircraft traffic and the consequent increase in atmospheric pollution, which increase in atmospheric pollution, which is is seen by the general public as exhaust seen by the general public as exhaust smoke. smoke.

3.3. A combustion chamber must beA combustion chamber must be able able to to operate efficiently over a wide operate efficiently over a wide range range of conditions of conditions (( e.g. inlet pressure e.g. inlet pressure & & temperature of air and air/fuel ratiostemperature of air and air/fuel ratios))..

4.4. In performing these functions, the flame In performing these functions, the flame tube and spray nozzle atomizer tube and spray nozzle atomizer

components must components must bebe mechanically mechanically reliablereliable..

5.5. The gas turbine engine operates on a The gas turbine engine operates on a constant constant pressure cycle, therefore, during the pressure cycle, therefore, during the

process process of combustionof combustion pressure loss pressure loss should be should be minimumminimum..

In providing adequate turbulence and In providing adequate turbulence and mixing, a mixing, a total pressure loss varying from about total pressure loss varying from about 3 - 8 %3 - 8 % of the air pressure at entry to the of the air pressure at entry to the chamber is chamber is incurred. incurred.

6.6. Combustion stability (i.e. Combustion stability (i.e. satisfactory satisfactory rich and weak mixture extinction rich and weak mixture extinction

limits)limits)

Combustion stabilityCombustion stability means smooth burning means smooth burning and the ability of the flame to remain alight and the ability of the flame to remain alight over a wide operating range. For any over a wide operating range. For any

particular particular type of combustion chamber there is type of combustion chamber there is both a both a rich and weak limit to the air/fuel ratio, rich and weak limit to the air/fuel ratio, beyond beyond which the flame is extinguished.which the flame is extinguished.

7.7. Uniform temperature and velocity Uniform temperature and velocity distribution at the entrance to the turbine distribution at the entrance to the turbine and simplicity of control.and simplicity of control.

8.8. Ease and cheapness of manufacture.Ease and cheapness of manufacture.

9.9. The containing walls and internal parts of the The containing walls and internal parts of the combustion chamber must becombustion chamber must be heat & heat & corrosion resistant corrosion resistant because it is because it is subjected subjected to the products to the products of the combustion, of the combustion, creep failure and fatigue due to thermal and creep failure and fatigue due to thermal and vibrational stresses.vibrational stresses.

1.1. Air from the engine compressor enters the Air from the engine compressor enters the combustion combustion chamber at a velocity up to 500 chamber at a velocity up to 500 feet per second, but feet per second, but because at this velocity because at this velocity the air speed is far too high for the air speed is far too high for combustion, combustion, the first thing that the chamber must do is to the first thing that the chamber must do is to diffuse it, i.e. decelerate it and ATF at normal diffuse it, i.e. decelerate it and ATF at normal mixture mixture ratios is only a few feet per second, ratios is only a few feet per second, any fuel lit even in the any fuel lit even in the diffused air stream, diffused air stream, which now has a velocity of about 80 which now has a velocity of about 80 feet per feet per second, would be blown away. A region of low second, would be blown away. A region of low axial velocity has therefore to be created in the axial velocity has therefore to be created in the chamber, so chamber, so that the flame will remain alight that the flame will remain alight throughout the range of throughout the range of engine operating engine operating conditions.conditions.

2.2. In normal operation, the overall air/fuel In normal operation, the overall air/fuel ratio of a combustion chamber can vary ratio of a combustion chamber can vary between 45:1 and 130:1, However, ATF will between 45:1 and 130:1, However, ATF will only burn efficiently at, or close to, a ratio of only burn efficiently at, or close to, a ratio of 15:1, so the 15:1, so the fuel must be burned with only fuel must be burned with only part of the air entering the chamber, in what part of the air entering the chamber, in what is called a primary combustion zone. This is is called a primary combustion zone. This is achieved by means of a flame tube achieved by means of a flame tube (combustion liner) that has various devices (combustion liner) that has various devices for metering the airflow distribution along for metering the airflow distribution along the chamber.the chamber.

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3.3. Approximately 20 per cent of the air mass flow is Approximately 20 per cent of the air mass flow is taken in by the snout or entry section. Immediately taken in by the snout or entry section. Immediately downstream of the snout are swirl vanes and a perforated downstream of the snout are swirl vanes and a perforated flare, through which air passes into the primary combustion flare, through which air passes into the primary combustion zone. The swirling air induces a flow upstream of the centre zone. The swirling air induces a flow upstream of the centre of the flame tube and promotes the desired recirculation. of the flame tube and promotes the desired recirculation. The air not picked up by the snout flows into the annular The air not picked up by the snout flows into the annular space between the flame tube and the air casing.space between the flame tube and the air casing.

7. 7. Through the wall of the flame tube body, adjacent to Through the wall of the flame tube body, adjacent to the combustion zone, are a selected number of the combustion zone, are a selected number of

secondary holes through which a further 20 per cent of secondary holes through which a further 20 per cent of the main flow of air passes into the primary zone. The the main flow of air passes into the primary zone. The air air from the swirl vanes and that from the secondary air from the swirl vanes and that from the secondary air holes interacts and creates a region of low velocity holes interacts and creates a region of low velocity recirculation. This takes the form of a toroidal vortex, recirculation. This takes the form of a toroidal vortex, similar to a smoke ring, which has the effect of similar to a smoke ring, which has the effect of stabilizing and anchoring the flame. The recirculating stabilizing and anchoring the flame. The recirculating gases hasten the burning of freshly injected fuel gases hasten the burning of freshly injected fuel droplets droplets by rapidly bringing them to ignition by rapidly bringing them to ignition temperature. temperature.

8.8. It is arranged that the conical fuel spray from the It is arranged that the conical fuel spray from the

nozzle intersects the recirculation vortex at its centre. nozzle intersects the recirculation vortex at its centre. This action, together with the general turbulence in the This action, together with the general turbulence in the primary zone, greatly assists in breaking up the fuel primary zone, greatly assists in breaking up the fuel and mixing it with the incoming air.and mixing it with the incoming air.

9. 9. The temperature of the gases released by The temperature of the gases released by combustion combustion is about 1,800 to 2,000 deg. C., which is far too is about 1,800 to 2,000 deg. C., which is far too hot for hot for entry to the nozzle guide vanes of the turbine. entry to the nozzle guide vanes of the turbine. The air The air not used for combustion, which amounts to not used for combustion, which amounts to about 60 about 60 per cent of the total airflow, is therefore per cent of the total airflow, is therefore introduced introduced progressively into the flame tube. progressively into the flame tube. Approximately a Approximately a third of this is used to lower the gas third of this is used to lower the gas temperature in the temperature in the dilution zone before it enters the dilution zone before it enters the turbine and the turbine and the remainder is used for cooling the walls remainder is used for cooling the walls of the flame of the flame tube. This is achieved by a film of cooling air tube. This is achieved by a film of cooling air flowing flowing along the inside surface of the flame tube wall, along the inside surface of the flame tube wall,

insulating it from the hot combustion gases. A recent insulating it from the hot combustion gases. A recent development allows cooling air to enter a network of development allows cooling air to enter a network of passages within the flame tube wall before exiting to passages within the flame tube wall before exiting to form an insulating film of air, this can reduce the form an insulating film of air, this can reduce the

required wall cooling airflow by up to 50 per cent. required wall cooling airflow by up to 50 per cent. Combustion should be completed before the dilution Combustion should be completed before the dilution air air enters the flame tube, otherwise the incoming air enters the flame tube, otherwise the incoming air will cool will cool the flame and incomplete combustion will the flame and incomplete combustion will result. result.

10. 10. An electric spark from an igniter plug initiates An electric spark from an igniter plug initiates combustion and the flame is then self-sustained. combustion and the flame is then self-sustained.

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