Turbine engine 1

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Turbine engine 1

  1. 1. TURBINE ENGINES    Design of a working gas turbine engine had been under way for years prior to WWII. The war effort had brought about many advances in gas turbine technology. Advantages over reciprocating engines: 1- Increased reliability. 2- longer mean times between overhaul. 3- higher airspeeds. 4- Ease of operation at high altitudes. 5- high power to engine weight ratio.
  2. 2. DESIGN AND CONSTRUCTION    Newton’s third law of motion states that for every action there is an equal and opposite reaction. A squid takes sea water into its body and uses its muscles to add energy to the water, then expels the water in the form of a jet. This action produces a reaction that propels the squid forward. Jet propulsion take a quantity of air and accelerating it through an orifice or nozzle.
  3. 3. DESIGN AND CONSTRUCTION         Hero devised a toy called aeolipile used the reaction principle. Inflated balloon is anther example of Newton’s reaction principle. Dr. Sanford Moss submitted his master thesis on gas turbine in 1900. He uses his concepts to develop turbo-supercharger. Frank Whittle of England uses Dr. Moss research to develop the first successful turbojet in 1930. The engine completed its first flight in 1941, producing about 1000 lb at a speed over 400 miles/hr. Hans Von Ohain, German engineer design and built a jet engine that produced 1100 lb and made its first flight in 1939. United states build its first jet engine which produces 1600 lb and made its first flight in 1942.
  4. 4. DESIGN AND CONSTRUCTION
  5. 5. JET PROPULSION TODAY    The majority of commercial aircraft utilize some form of jet propulsion. Development of military and commercial aircraft that moves faster than the speed of sound. Extremely popular for use on business jets.
  6. 6. TYPES OF JET PROPULSION 1- ROCKET. 2- RAMJET. 3- PULSEJET. 4- GAS TURBINE ENGINE.
  7. 7. ROCKET       Non air breathing engine that carries its own fuel as well as the oxygen needed for the fuel burn. Types of rockets: 1- solid-propellant rockets. 2- liquid-propellant rockets. Solid- propellant rockets use a solid fuel that is mixed with an oxidizer and shaped into a specific shape that promotes an optimum burning rate. Produce extremely high velocity, and used to propel some weapons and to provide additional thrust for take off of heavy loaded aircraft. Liquid-fuel rocket uses fuel and oxidizing agent such as liquid oxygen carried in tanks aboard the rocket. When mixed the reaction is so violent that produce a tremendous amount of heat.
  8. 8. ROCKET
  9. 9. RAMJET Ramjet engine is an athodyd, or aero-thermodynamic-duct.  Air breathing engine with no moving parts.  Must be moved forward at a high velocity before it can produce thrust.  Limited in there use, military weapons delivery systems. 
  10. 10. PULSEJET     Similar to ramjet except that the air intake duct is equipped with a series of shutter valves. Shutter valves are spring loaded to the open position. Air is drawn and mixed with fuel in the combustion chamber, as pressure build up the shutter valves closes causing the air to expand backward. More useful than ramjet because it will produce thrust prior to being accelerated to a high speed.
  11. 11. GAS TURBINE ENGINE    The most practical form of jet engine in use today. The standard on nearly all transport and military aircraft. Types of gas turbine engines: 1- Turbojet. 2- Turboprop. 3- Turboshaft. 4- Turbofan.
  12. 12. TURBOJET ENGINES     Straight forward operating principle. Air enters through the air intake, compressed by the compressor, fuel is added and burned in the combustion chamber, heat causes the compressed air to expand rearward, passes through the turbine and spins it, which drives the compressor, and the air then exit the engine at a much higher velocity than the incoming air. The difference between the entering air and the exiting gases that produces the thrust. EPR is the ratio of the turbine discharge pressure to engine inlet air pressure.( EPR probes)
  13. 13. TURBOJET ENGINES
  14. 14. TURBOJET ENGINES
  15. 15. TURBOPROP ENGINES     Turboprop engine is a gas turbine engine that delivers power to a propeller. Power produced by a turboprop is delivered to a reduction gear system that spins a propeller. Used in business and commuter type aircraft because of the combination of jet power and propeller efficiency at speeds between 300 and 400 mph. Provide the best specific fuel consumption of any gas turbine engine.
  16. 16. TURBOPROP ENGINES
  17. 17. TURBOSHAFT ENGINES     Turboshaft engine is a gas turbine engine that delivers power to a shaft that can drive something else. Most of the energy produced by the expanding gases is used to drive a turbine. Helicopters, auxiliary power units, electric generators, and surface transportation systems use turboshaft engines. Turboshaft engine power is measured in shaft horsepower.
  18. 18. TURBOSHAFT ENGINES
  19. 19. TURBOFAN ENGINES    Consist of a multi-bladed ducted propeller driven by a gas turbine engine. Provide a compromise between the best features of the turbojet and the turboprop. Have turbojet-type cruise speed capability, yet retain some of the short-field takeoff capability of a turboprop.
  20. 20. TURBOFAN ENGINES
  21. 21. TURBOFAN ENGINES    Forward-fan engines have the fan mounted in the front of the compressor. Aft-fan mounted engines have the fan mounted to the turbine section. Inlet air is divided into two separate streams. ( engine core air, bypass air).
  22. 22. TURBOFAN ENGINES
  23. 23. TURBOFAN ENGINES     Thrust ratio, bypass ratio, and fan pressure ratio are the terms you should be familiar with. Thrust ratio is the comparison of the thrust produced by the fan to the thrust produced by the engine core exhaust. Bypass ratio is the ratio of incoming air to that bypasses the core to the amount of air that passes through the engine core. Fan pressure ratio is the ratio of air pressure leaving the fan to the air pressure entering the fan.
  24. 24. TURBOFAN ENGINES     Turbofan engines are divided into three classification based on bypass ratio: 1- low bypass (1:1). 2- medium bypass (2:1 or 3:1). 3- high bypass (4:1 or greater). Low bypass engine, bypass air could be ducted directly overboard through a short fan duct or in a ducted fan where the bypass air is ducted along the entire length of the engine. Full fan ducts reduce aerodynamic drag and noise emissions. Both use a converging discharge nozzle that increases velocity and produce thrust.
  25. 25. TURBOFAN ENGINES
  26. 26. TURBOFAN ENGINES     Medium bypass engines have thrust ratio similar to their bypass ratios. Fan diameter determines a fan’s bypass ratio and thrust ratio. High bypass ratio engines use the largest diameter fan of any of the bypass engines. Offer higher propulsive efficiencies and better fuel economy of low and medium bypass engines.
  27. 27. TURBOFAN ENGINES
  28. 28. TURBOFAN ENGINES      Fan pressure ratio is the ratio of air pressure leaving the fan to the air pressure entering the fan. Ranging from 1.5:1 on a low bypass engines up to 7:1 on some high bypass engines. Most high bypass ratio engines use high aspect ratio blades. Aspect ratio is the ratio of a blade’s length to its width, or cord. Low aspect ratio blades are desirable because of their resistance to foreign object damage, especially bird strikes.
  29. 29. UNDUCTED FAN ENGINES    Ultra high bypass (UHB) propfan and unducted fan engine (UDF) are recently developed engines with higher efficiencies than any engine in use. Better fuel economy than high bypass turbofan engines. Achieve 30:1 bypass ratio by using single or dual propellers made of composite blades that are 12 to 15 feet in diameter.
  30. 30. UNDUCTED FAN ENGINES
  31. 31. ENGINE COMPONENTS  Basic section of gas turbine engine: 1- Air inlet. 2- Compressor section. 3- Combustion section. 4- Turbine section. 5- Exhaust section. 6- Accessory section. 7- Necessary auxiliary systems.
  32. 32. ENGINE COMPONENTS
  33. 33. AIR INLET DUCTS    Normally considered to be a part of the airframe rather than the engine. Functions of air inlet duct: 1- (ram or pressure recovery) to recover as much of the total pressure of the free airstream as possible and deliver it to the compressor. 2- Shaped to raise the air pressure above atmospheric pressure . 3- Provide a uniform supply of air to the compressor so it can operate efficiently. 4- Must cause as little drag as possible. Ram effect results from forward movement which causes the air to pile up in the air inlet.
  34. 34. AIR INLET DUCTS
  35. 35. AIR INLET DUCTS     Inlet ducts are mounted : 1- On the engine. 2- In the wing. 3- On the fuselage. Engine mounted inlets: Used on several large commercial and military aircraft. The air inlet is located directly in front of the compressor and is mounted to the engine.
  36. 36. AIR INLET DUCTS
  37. 37. AIR INLET DUCTS   Wing mounted inlets: On some aircraft where the engines are mounted inside the wings. Typically wing mounted inlets are positioned near the wing root.
  38. 38. AIR INLET DUCTS     Fuselage-mounted inlets: Engines mounted inside a fuselage typically use air inlet ducts located near the front of the fuselage. Used on many old military and modern supersonic aircraft. Using this type allow the manufacturer to build more aerodynamic aircraft. Some military aircraft use air inlet ducts mounted on the sides of the fuselage.
  39. 39. AIR INLET DUCTS
  40. 40. AIR INLET DUCTS Types of air inlet ducts: 1- Subsonic inlets. 2- Supersonic inlets. 3- Bellmouth inlets.
  41. 41.     Subsonic inlets Fixed geometry duct whose diameter progressively increases from front to back. In a divergent duct as the intake air spreads out, the velocity of the air decreases and the pressure increases. The increased pressure increase the engine efficiency when it reach its designed cruise speed. ( optimum aerodynamic efficiency, best fuel economy). Inlet, compressor, combustor, turbine, and exhaust duct are designed to match each other at this speed as a unit.
  42. 42. Subsonic inlets
  43. 43. Supersonic inlets    Fixed or variable geometry whose diameter progressively decreases, then increases from front to back. Convergent-divergent duct used to slow the incoming air to subsonic speed before it reaches the compressor. Movable plug or throat changes the duct geometry to accommodate a wide range of flight speeds.
  44. 44. Supersonic inlets
  45. 45. Supersonic inlets
  46. 46. Bellmouth inlets    Convergent profile that is designed for obtaining very high aerodynamic efficiency when stationary or in slow flight. Used on helicopters, some slow moving aircraft, and ground run stands. Short in length and has rounded shoulders offering very little air resistance.
  47. 47. Bellmouth inlets
  48. 48. FOREIGN OBJECT DAMAGE (F.O.D)   Prevention of F.O.D. is a top priority among turbine engine operators. Methods of FOD prevention: 1- Inlet screen over an engine inlet duct. 2- Sand or ice separators. 3- Vortex dissipater, vortex destroyer, blowaway jet.
  49. 49. FOREIGN OBJECT DAMAGE (F.O.D)    The use of inlet screen is common on many rotorcraft and turboprop engines and on engine installed in test stand. Inlet screen is not used on high mass airflow engines. Sand or ice separator consists of an air intake with at least one venturi and a series of sharp bends.
  50. 50. Sand or ice separators
  51. 51. Sand or ice separators
  52. 52. VORTEX DISSIPATER     Some engines form a vortex between the ground and the ground and the inlet during ground operations. This vortex can lift water and debris or small hardware and direct it to the engine. Vortex dissipater routes high pressure bleed air to a discharge nozzle between the ground the air inlet to prevent vortex from developing. Landing gear switch arms the dissipater when ever the aircraft is on ground.
  53. 53. VORTEX DISSIPATER
  54. 54. COMPRESSOR SECTION    The more air that is forced into an engine, the more thrust the engine can produce. Modern compressors must increase the intake air pressure 20 to 30 times above the ambient air pressure and move the air at a velocity of 400 to 500 feet per second. Compressor pressure ratio is the ratio of the compressor discharge static pressure to the inlet air static pressure.
  55. 55. COMPRESSOR SECTION  Functions of compressors: 1- Support the combustion and provide the air necessary to produce thrust. 2- Supplies bleed air : a- to cool the hot section. b- heated air for anti-icing. c- cabin pressurization and air conditioning. d- fuel system deicing. e- pneumatic engine starting.
  56. 56. COMPRESSOR SECTION TYPES OF COMPRESSORS 1- CENTRIFUGAL FLOW COMPRESSOR.  2- AXIAL FLOW COMPRESSOR. Each is named according to the direction the air flows through the compressor.
  57. 57. CENTRIFUGAL FLOW COMPRESSOR    Some times called radial outflow compressor. Earliest compressor design and still in use in some small engines and APU’s. Consist of : 1- impeller or rotor. 2- diffuser. 3- manifold.
  58. 58. CENTRIFUGAL FLOW COMPRESSOR
  59. 59. CENTRIFUGAL FLOW COMPRESSOR       Impeller or rotor: Consist of forged disc with integral blades, fastened by a splined coupling to a common power shaft. The function of the impeller is to take the air in and accelerate it outward by centrifugal force. Single stage compressors have only one impeller. Two stage compressors have two impellers. Double-sided or double entry compressors have two impellers mounted back to back.
  60. 60. SINGLE STAGE COMPRESSOR
  61. 61. DOUBLE-STAGE COMPRESSOR
  62. 62. DOUBLE-SIDED COMPRESSOR
  63. 63. CENTRIFUGAL FLOW COMPRESSOR   The use of more than two stages in a compressor is impractical: 1- Energy lost when the air flow slows down as it passes from one impeller to the next. 2- The added weight from each impeller requires more energy from the engine to drive the compressor. Double sided impeller allows a higher mass air flow than single impeller compressor. But the ducting to get the air from one side of the impeller to the other is complicated.
  64. 64. CENTRIFUGAL FLOW COMPRESSOR   Diffuser, a divergent duct where the air loses its velocity and increases its pressure. In a divergent duct, air spreads out, slows down and increases in static pressure.
  65. 65. CENTRIFUGAL FLOW COMPRESSOR      Compressor manifold distributes the air in a smooth flow to the combustion section. The manifold has one outlet for each combustion chamber so the air is evenly divided. Outlet ducts is an elbow mounted to the outlet ports to act as air duct. Outlet ducts change the radial direction of the air to an axial direction. Turning vanes or cascade vanes help changing the direction of the air with minimum energy loses.
  66. 66. CENTRIFUGAL FLOW COMPRESSOR
  67. 67. CENTRIFUGAL FLOW COMPRESSOR  Advantages of centrifugal compressor: 1- Simplicity of manufacture. 2- Relatively low cost, low weight, low starting power requirements. 3- Operating efficiency over a wide range of rotational speeds. 4- Accelerate air rapidly and immediately deliver it to the diffuser. 5- Tip distance may reach 1.3 mach with out air flow separation. 6- High pressure rise per stage.
  68. 68. CENTRIFUGAL FLOW COMPRESSOR  Disadvantages of centrifugal compressor: 1- large frontal area, which mean increased aerodynamic drag. 2- limited number of stages restrict its uses to smaller and less powerful engines.
  69. 69. Principles of operation     The impeller is rotated at high speed by the turbine and air is continuously induced into the centre of the impeller. Centrifugal action causes it to flow radially outwards along the vanes to the impeller tip, thus accelerating the air and also causing a rise in pressure to occur. The engine intake duct may contain vanes that provide an initial swirl to the air entering the compressor . The air, on leaving the impeller, passes into the diffuser section where the passages form divergent nozzles that convert most of the kinetic energy into pressure energy.
  70. 70. CENTRIFUGAL FLOW COMPRESSOR    To maximize the airflow and pressure rise through the compressor requires the impeller to be rotated at high speed, therefore impellers are designed to operate at tip speeds of up to 1,600 ft. per sec. By operating at such high tip speeds the air velocity from the impeller is increased so that greater energy is available for conversion to pressure. To maintain the efficiency of the compressor, it is necessary to prevent excessive air leakage between the impeller and the casing; this is achieved by keeping their clearances as small as possible
  71. 71. AXIAL FLOW COMPRESSOR       Consist of : 1- ROTOR. 2- STATOR. The rotor consist of rows of blades fixed on a rotating spindle. The angle and airfoil contour forces the air backward as a propeller. The stator vanes are arranged infixed rows between the rows of rotor blades and act as a diffuser at each stage. Stators decrease the air velocity and raise the pressure. Each pressure stage consist of one row of blades and one row of vanes.
  72. 72. AXIAL FLOW COMPRESSOR
  73. 73. AXIAL FLOW COMPRESSOR      Single stage in an Axial compressor is capable of rising the pressure ratio of only 1.25 : 1. High compressor pressure ratio is obtained by adding more stages. Unlike centrifugal compressors, axial flow compressors raise the air pressure rather than the velocity. The rotor of each stage rise the velocity of the air while the stator vanes diffuse the air, slowing it and increase the pressure. The overall result is increased air pressure and relatively constant velocity.
  74. 74. AXIAL FLOW COMPRESSOR
  75. 75. AXIAL FLOW COMPRESSOR     The space between the rotor shaft and the stator casing gradually decreases from front to back. This shape is necessary to maintain a constant air velocity as air density increases. The case of most axial compressors is horizontally divided into two halves. Bleed air ports are provided on the comp. case for ancillary functions.
  76. 76. AXIAL FLOW COMPRESSOR
  77. 77. AXIAL FLOW COMPRESSOR   Disadvantage of axial compressor: 1- High weight 2- High starting power requirements. 3- Low pressure rise per stage. 4- Expensive and difficult to manufacture. Advantages over radial flow compressors: 1- High ram efficiency. 2- The ability to obtain higher compressor pressure ratio. 3- Reduced aerodynamic drag because of small frontal area.
  78. 78. COMPRESSOR ROTOR BLADES    Aerofoil cross-section with a varying angle of incidence or twist blades. The twist compensates for the blade velocity variation between the tip and the root. Axial flow compressors typically have 10 to 18 compression stages.
  79. 79. COMPRESSOR ROTOR BLADES       The roots of the blades often fits loosely into the rotor, to allow for easy assembly and vibration damping. As the blades rotate the centrifugal force keeps the blades in their correct position. Bulb, Fir tree, or dovetail are the design of rotor blades roots. The blades is secured in their position by using a pin and lock tab or locker. Some long fan blades have a mid-span shroud that helps support the blades, making them more resistant to the bending force created by airstream. Shingling happen when the mating surfaces on a mid-span shroud become excessively worn and the shrouds overlap.
  80. 80. COMPRESSOR ROTOR BLADES
  81. 81. COMPRESSOR ROTOR BLADES        Flat machine tip blade is cut off square at the tip. Profile tip blade have a reduced thickness at the tips. Profiling a compressor blade increases its natural vibration frequency, which reduce the blade vibration tendency. Thin trailing edge of profile tipped blades causes a vortex which increases air velocity and prevent air from spilling back over the blade tip. Tight clearance around the blade tips of some newer engine is accomplished by using a shroud strip of abradable material. Localized increase in blade camber, both at blade tip and root increases compressor efficiency. The increased blade camber overcome the friction caused by the boundary layer of air near the compressor case. (end bend).
  82. 82. COMPRESSOR ROTOR BLADES
  83. 83. COMPRESSOR STATOR VANES      Stator vanes is stationary blades located between rows of rotating blades. Act as diffusers for the air coming off the rotor decreasing its velocity, increasing pressure, prevent swirling, and direct the flow of air to the next stage. Stator vanes are made of steel, nickel, and titanium. Secured directly to the compressor casing or to a stator vane retaining ring. Stator vanes are often shrouded at their tips to minimize vibration.
  84. 84. COMPRESSOR STATOR VANES
  85. 85. COMPRESSOR STATOR VANES     Inlet guide vanes are a set of stator vanes immediately in front of the first stage rotor blades. Inlet guide vanes direct the airflow into the first stage rotor blades at the best angle, to improve the aerodynamics of the compressor by reducing the drag on the 1st rotor blades. To maintain proper airflow through the engine, variable IGV’s and several stator vanes are used on some high compressor pressure ratio engines. The outlet vane assembly is the last set of vanes that straighten the air flow and eliminate any swirling motion or turbulence.
  86. 86. COMPRESSOR STATOR VANES
  87. 87. MULTIPLE-SPOOL COMPRESSORS   Single spool compressor has only one compressor unit connected to the turbine. Drawback of single spool compressors: 1- rear stages operate at a fraction of their capacity, while the forward stages are overloaded. 2- does not respond quickly to sudden control input changes.  Single-spool compressors are relatively simple and inexpensive.
  88. 88. MULTIPLE-SPOOL COMPRESSORS
  89. 89. MULTIPLE-SPOOL COMPRESSORS       Single spool compressor Drawbacks were overcome by splitting the compressor into two or three sections. Each compressor is connected to its turbine by shafts that run coaxially, one within the other. Dual-spool, twin-spool compressors has two compressors connected to two turbines. Front section is called low pressure, low speed, or N1 compressor. Driven by 2 stage low pressure turbine (rear turbine). Second compressor is called high pressure, high speed, or N2 compressor. Driven by single stage high pressure turbine (front turbine). The low pressure compressor is driven by the high pressure turbine by a shaft that rotate inside the high pressure compressor shaft.
  90. 90. MULTIPLE-SPOOL COMPRESSORS
  91. 91. MULTIPLE-SPOOL COMPRESSORS       Since the spools are not connected together, each is free to seek its own best operating speed. High pressure compressor speed is relatively constant. Low pressure compressor speeds up or slows down with changes in the inlet sir flow caused by flight condition. N1 increases at high altitude and decreases at low altitude to supply the high pressure compressor with constant air pressure and mass flow for each power setting. Triple-spool compressor turbo-fan engine has three compressors connected to three turbines. The fan, low pressure, or N1 compressor, the next in line is called intermediate or N2 compressor, and the inner most is called high pressure or N3 compressor.
  92. 92. MULTIPLE-SPOOL COMPRESSORS
  93. 93. COMPRESSOR STALL     Compressor blades are airfoils, so its subjected to the same aerodynamic principles as aircraft wings. Compressor blade has an angle of attack which is : an acute angle between the chord line and the relative wind. The angle of attack of a compressor blade is the result of inlet air velocity and the compressor’s rotational velocity.( vector ) Quantity to the approaching inlet air. Compressor stall is an imbalance between the two vector quantities, inlet velocity and compressor rotational speed.
  94. 94. COMPRESSOR STALL     Compressor stall occur when the compressor blade’s angle of attack exceeds the critical angle of attack. Smooth airflow is interrupted and turbulence is created with pressure fluctuations. During stall airflow in the compressor slow down and stagnate sometimes reverse direction. Heard as pulsating or fluttering sound in its mildest form to a loud explosion in its most developed state.
  95. 95. COMPRESSOR STALL     Cockpit indications for compressor stall: 1- fluctuations in rpm. 2- increase in exhaust gas temperature. Transient stall are mild and not harmful to the engine, and often correct themselves easily. Sever or hung stall can significantly impair engine performance, cause loss of power and can damage the engine. Reducing the angle of attack on the rotor blades is the only way to overcome a stalled condition.
  96. 96. COMPRESSOR STALL   Methods of preventing compressor stall: 1- Variable inlet guide vanes and stator vanes. 2- Air-bleed valves. Reasons of compressor stall: 1-When A/C flies in sever turbulence or performs abrupt flight maneuvers. 2- Excessive fuel flow caused by sudden engine acceleration. 3- Contamination or damaged compressor blades, stator vanes or turbine components. (FOD)
  97. 97. AIR-BLEED VALVE
  98. 98. COMBINATION COMPRESSORS   Axial flow-centrifugal flow compressors were developed to combine the best features of centrifugal and axial compressors. Currently used in some smaller engines installed on business jets and helicopters.
  99. 99. COMPRESSOR AIR BLEED Compressor supplies high pressure, high temperature air for various secondary functions such as:  Cabin pressurization. 2. Heating. 3. Cooling. 4. Deicing. 5. Anti-icing. 6. Pneumatic engine starting. 1.
  100. 100. COMPRESSOR AIR BLEED Bleed air or customer bleed air is tapped from the compressor through bleed ports at various stages.  Bleed port is a small opening adjacent to the compressor stage selected for bleed air supply.  The required air pressure and temperature determine the compressor stage to bleed air from.  The air bled from the last stage often need cooling because the air temperature would be very high because of compression. (650ْ F).  Bleeding air dose cause a small drop in engine power, power loss can be detected by observing EPR, and EGT. 
  101. 101. COMPRESSOR AIR BLEED
  102. 102. DIFFUSER    The divergent shape of a diffuser slows compressor discharge while at the same time increase its pressure to the highest value in the engine. Air speed must be slowed to support combustion. Diffuser is a separate section bolted to the rear of the compressor ahead of the combustion section.
  103. 103. COMBUSTION SECTION   Located directly between the compressor diffuser and turbine section. Basic components of combustion section: 1- one or more combustion chambers (combustors). 2- fuel injection system. 3- ignition source. 4- fuel drainage system.
  104. 104. COMBUSTION SECTION    Combustion chamber or combustors is where the fuel and air are mixed and burned. Consist of an outer casing with a perforated inner liner. Perforation are various shapes and sizes that effect the flame propagation within the liner.
  105. 105. COMBUSTION SECTION     Fuel injection system meters the right amount of fuel through the fuel nozzles. Fuel nozzles are located in the combustion chamber case or compressor outlet elbow. Fuel is sprayed in a finely atomized spray into the liner. The finer the spray the more rapid and efficient the combustion process.
  106. 106. COMBUSTION SECTION      High energy capacitor discharge system is typically used as ignition source for turbine engine. Ignition system produces 60 to 100 sparks per minute. A ball of fire results at the igniter electrodes. Some systems can shoot sparks several inches. Care must be taken to avoid lethal shock during maintenance.
  107. 107. COMBUSTION SECTION    Unburned fuel is drained out after engine shut down. Draining the unburned fuel eliminates engine fire after shutdown, and reduces the possibility of exceeding tail pipe or turbine inlet temperature. Helps to prevent gum deposits in the fuel manifold and the combustion chamber.
  108. 108. COMBUSTION SECTION  To accomplish the task of burning the fuel air mixture efficiently the C.C must: 1- Mix fuel and air effectively in the best ratio for good combustion. 2- Burn the mixture as efficiently as possible. 3- Cool the hot combustion gases to a temperature the turbine blades can tolerate. 4- Distribute hot gases evenly to the turbine section.
  109. 109. COMBUSTION SECTION       Air flow through the combustor is divided into primary and secondary paths. 25 to 35 % of the incoming air is primary. 65 to 75 % of the incoming air is secondary. Primary or combustion air is directed inside the liner, passing through a set of swirl vanes which give the air a radial motion. As air is swirled the speed is reduced to about five to six feet per second. Its important to slow the air to prevent flameout.
  110. 110. COMBUSTION SECTION       Radial motion generate a vortex in the flame area which properly mix the fuel and air. The combustion process is completed in the first third of a combustor. The secondary air flow at high speed (several hundred feet per sec.) around the combustor’s periphery. Secondary air forms a cooling blanket on both sides of the liner and centers the combustion flames. Some air enters the combustors through the perforations to ensure the burning of any remaining fuel. Secondary air mix with the combustion gases to provide an even distribution of energy to the turbine nozzle.
  111. 111. COMBUSTION SECTION
  112. 112. COMBUSTION SECTION  Types of combustion chambers: 1- Multiple-can type. 2- Annular type and reverse flow annular type. 3- Can-annular type
  113. 113. MULTIPLE-CAN TYPE        Consist of a series of individual combustor cans which acts as individual burner units. Well suited to centrifugal compressor engines. Each Can has a case and a perforated stainless steel liner. Inner liner is heat resistant and easily removed for inspection. Each Can has a large curvature to provide high resistance to warpage. Tow igniter plugs in two cans start the combustion, then the flame is traveled to the other cans by flame propagation tubes (interconnectors). Each flame propagation tubes is a small tube surrounded with larger tube or jacket.
  114. 114. MULTIPLE-CAN TYPE
  115. 115. MULTIPLE-CAN TYPE
  116. 116. ANNULAR TYPE       Commonly used on small and large engines. The most efficient for thermal efficiency, weight, and physical size. Consist of a housing and a perforated inner liner or basket. The liner is single unit that encircle the turbine shaft. An annular combustor with two baskets is known as a double annular combustion chamber. Two igniters are used to ignite the fuel/air mixture.
  117. 117. ANNULAR TYPE
  118. 118. ANNULAR TYPE        Air flow enters at the front and is discharged at the rear with primary and secondary airflow. Must be removed as one unit for repair or replacement. Reverse flow combustors are designed so the airflow can reverse direction. The combustion gases enters from the rear and flowing in the opposite direction of the normal airflow through the engine. The turbine wheels are inside the combustor area, which allow for a shorter and lighter engine. Compressor discharge air is preheated as it passes around the combustion chamber. Lighter weight and air preheat make up for the losses caused by the reversing of the direction of the air.
  119. 119. ANNULAR TYPE
  120. 120. CAN-ANNULAR TYPE        Combination of the multiple-can and annular type combustors. Consist of a casing that encircles multiple cans (liners) assembled radially around the engine axis. A fuel nozzle cluster is attached at the forward end of each burner can. Pre-swirl vanes are placed around each fuel nozzle. (through fuel mixing and slow the air). Tow igniter plugs initiate the combustion and propagation tubes connect the liners. Each can and its liner removed individually for maintenance. Combine the ease of overhaul and testing of multiple-can combustors with the compactness of annular combustors.
  121. 121. CAN-ANNULAR TYPE
  122. 122. FLAME OUT      High air flow rate or excessively slow airflow can extinguish the combustion flame. Flameout is uncommon in modern engine but if the correct set of circumstances can cause engine die out. Turbulent weather, high altitude, slow acceleration, and high speed maneuvers can induce a flameout. Lean die-out occurs at high altitude where low engine speeds and low fuel pressure form a weak flame that can die out in normal airflow. Rich blow-out occurs during rapid engine acceleration when an overly rich mixture causes the fuel temperature to drop below the combustion temperature or when there is insufficient airflow to support combustion.
  123. 123. TURBINE SECTION    Transforms a portion of the kinetic energy in the hot exhaust gases into mechanical energy to drive the compressor and accessories. In a turbojet engine the turbine absorbs approximately 60 to 80 % of the total pressure energy from exhaust gases. Consist of: 1- case. 2- stator. 3- shroud. 4- rotor.
  124. 124. TURBINE SECTION
  125. 125. TURBINE SECTION   TURBINE CASING Encloses the turbine rotor and stator assembly, support the stator elements. Has flanges on both ends that provide a means of attaching the turbine section to the combustion section and the exhaust assembly.
  126. 126. TURBINE SECTION       TURBINE STATOR Stator element, turbine nozzle, turbine guide vanes, and nozzle diaphragm. Located directly aft of the combustion section and immediately forward of the turbine wheel. Exposed to the highest temperatures in a gas turbine engine. Function: To collect the high energy airflow from the combustors and direct the flow to strike the turbine rotor at the appropriate angle. The stator vanes form a converging nozzles which convert some of the pressure energy to velocity energy. The velocity energy of the exhaust gases is converted to mechanical energy by the rotor blades.
  127. 127. TURBINE SECTION      TURBINE SHROUD Turbine nozzle assembly consist of an inner and outer shroud that retains and surround the nozzle vanes. The vanes are assembled between the inner and outer shroud in deferent methods. The nozzle vanes must be constructed to allow for thermal expansion, to prevent distortion or warping of the nozzle assembly. Installing the vanes loosely in the inner and outer shrouds and encase them in an inner and outer support rings allow thermal expansion of the vanes. Rigidly weld or rivet the vanes into the inner and outer shrouds which are cut into segments that have gaps between them allow for expansion.
  128. 128. TURBINE SECTION
  129. 129. TURBINE SECTION     TURBINE ROTOR Consist of a shaft and a turbine rotor, or wheel. Turbine wheel is a dynamically balanced unit consisting of blades attached to a rotating disk. The disk is the anchoring component for the turbine blades and bolted or welded to the shaft. The shaft rotates in bearing that are lubricated by oil between the outer race and the housing to reduce vibration and allows for a slight misalignment in the shaft.
  130. 130. TURBINE SECTION     TURBINE ROTOR The high velocity gases pass through the turbine nozzle to rotate the turbine wheel. Many engines use multiple turbine stages to absorb sufficient energy to drive the compressor. The turbine is exposed to high rotational speed and elevated operating temperature stress. This stress could lead to turbine bleed growth or creep.
  131. 131. TURBINE SECTION
  132. 132. TURBINE SECTION        TURBINE BLADES Airfoil shaped designed to extract the maximum amount of energy from the hot gases. Blades are either forged or cast. Steel forged or cast nickel-based alloys. Development of reinforced ceramic holds promise. Blades fit loosely into turbine disk when cold, and expand to fit tightly when hot. Fir tree slots is the most commonly used method for attaching turbine blades. The blade may be retained in its groove by peening, welding, rivets, or lock tabs.
  133. 133. TURBINE SECTION
  134. 134. TURBINE SECTION  TURBINE BLADES Classification of turbine blades: 1- Impulse. 2- Reaction. 3- Impulse-Reaction.
  135. 135. TURBINE SECTION   IMPULSE TURBINE BLADES The total pressure drop across each stage occurs in the fixed nozzle guide vanes which, because of their convergent shape, increase the gas velocity whilst reducing the pressure. Turbine blades absorb the force required to change the direction of airflow and change it to rotary motion.
  136. 136. IMPULSE TURBINE BLADES
  137. 137. TURBINE SECTION    REACTION TURBINE BLADES Turning force is produced based on an aerodynamic action. The turbine blades form a series of converging duct that increase gas velocity and reduce pressure. Reduced pressure produces a lifting force that rotate the turbine wheel.
  138. 138. REACTION TURBINE BLADES
  139. 139. TURBINE SECTION IMPULSE REACTION TURBINE BLADES  Most modern engines uses impulse-reaction turbine blades.  Evenly distribute the workload along the length of the blade.  The blade base is impulse shaped while the blade tip is reaction shaped.  Creates a uniform velocity and pressure drop across the entire blade length.
  140. 140. TURBINE SECTION
  141. 141. TURBINE SECTION       TURBINE BLADES Can be open or shrouded at their tips. Open ended are used on high speed turbines, shrouded ended are used on slower rotational speed turbines. The end of each blade has a shroud attached to its end, once installed the shrouds contact each other and provide support. The shroud reduces the vibration and prevent the air from escaping over the blades tips. The added weight cause the turbine blades to be more susceptible to blade growth. A knife edge seal is machined around the outside of the shroud which reduces air losses at the blade tip.
  142. 142. TURBINE SECTION
  143. 143. TURBINE SECTION      COOLING The most limiting factor in running a gas turbine engine is the temperature. The higher the temperature raises, the more power or thrust an engine can produce. The effectiveness of a turbine engine’s cooling system plays a big role in engine performance. Cooling systems allow the turbine to operate 600 to 800 ْ F above the temperature limits of their metal alloys. Engine bleed air is used to cool the components in the turbine section.
  144. 144. TURBINE SECTION      COOLING Turbine disk absorb heat from the hot gases passing around their rim and the heat conducted from the turbine blades. Cooling air is directed over each side of the disk. Convection cooling or film cooling is the type of cooling used to cool turbine blades and vane by directing compressor bleed air through the hollow blades and out through holes in the tip, leading edge, and trailing edge. Some vanes are constructed of a porous high temp material, bleed air is ducted into the vane and exits through the porous material (transpiration cooling). The turbine vane shrouds may also be perforated with cooling holes.
  145. 145. TURBINE SECTION
  146. 146. TURBINE SECTION
  147. 147. COUNTER-ROTATING TURBINE   Not common on large engine. Effective in damping gyroscopic effects and reduce engine vibration.
  148. 148. EXHAUST SECTION    Exhaust section determine to some extent the amount of thrust developed. The size and shape of exhaust section affect: 1- Turbine inlet temperature. 2- the mass air flow through the engine. 3- The velocity and pressure of the exhaust jet. Exhaust section extend from the rear of the turbine section to the point where the exhaust gases leave the engine.
  149. 149. EXHAUST SECTION  The exhaust section consist of: 1- Exhaust cone. 2- Exhaust duct or tail pipe. 3- Exhaust nozzle.
  150. 150. EXHAUST SECTION EXHAUST CONE       Consist of: 1- Outer duct or shell. 2- Inner cone or tail cone. 3- Hollow struts. 4- Tie rods. The outer duct is made of stainless steel and attached to the rear flange of turbine section. Purpose of the tail cone is to channel and collect turbine discharge gases into a single jet. The outer duct and the inner cone form a divergent duct, so the air pressure increases and velocity decreases. Hollow struts support the inner cone and help straighten the swirling exhaust gases. The tie rods assist the struts in centering the inner cone within the outer duct.
  151. 151. EXHAUST SECTION
  152. 152. EXHAUST SECTION     TAIL PIPE An extension of the exhaust section that directs exhaust gases safely from the exhaust cone to the nozzle. Tail pipe cause heat and friction losses that causes drop in exhaust gas velocity and thrust. Used with engines that are installed within the fuselage to protect the surrounding airframe. On engine that require no tailpipe, the nozzle is mounted directly to the exhaust cone assembly.
  153. 153. EXHAUST SECTION     EXHAUST NOZZLE Provides the exhaust gases with the final boost in velocity. Converging design and the converging-diverging design used on aircraft. Converging design produces a venturi that accelerates the exhaust gases and increases engine thrust. Converging-diverging diameter decrease then increase from front to back which increase the velocity of exhaust gases above the speed of sound.
  154. 154. EXHAUST SECTION     The flow of cool and hot gases in a ducted low by pass turbofan engine combined in a mixer unit. High bypass turbofan engines exhaust the two streams separately through two sets of nozzles arranged coaxially around the exhaust nozzle. On some high pass engines a common or integrated nozzle is used to mix the hot and cold gases prior to their ejection. Exhaust nozzle opening can be fixed or variable geometry.
  155. 155. EXHAUST SECTION
  156. 156. AFTERBURNERS      Used to accelerate the exhaust gases to increase thrust. Installed after the turbine and in front of exhaust nozzle. Consist of fuel manifold, ignition source and flame holder. The gases in the tailpipe sill contain a large quantity of oxygen. Fuel manifold consist of fuel nozzle or spray bars inject fuel into the tailpipe.
  157. 157. AFTERBURNERS
  158. 158. THRUST REVERSERS     The brakes are unable to slow the A/C adequately during landing. Brake wear would be prohibitive and heat buildup could lead to brake fire. Most turbojet and turbofan powered A/C are fitted with thrust reversers to assist in braking. Thrust reversers redirect the flow of gases to provide thrust in the opposite direction.
  159. 159. THRUST REVERSERS
  160. 160. THRUST REVERSERS
  161. 161.         ACCESSORY SECTION Functions of accessory drive section 1- Used to power both engine and aircraft accessories. 2- Act as an oil reservoir or sump and housing the accessory drive gears and reduction gears. Accessory drive could located at engine’s midsection or front or rear of the engine. Rear mounted gear boxes allow the narrowest engine diameter and lowest drag configuration. Bevel gear drive the gear box using engine main power shaft. The gear box distributes power to each accessory drive pad. Reduction gear is necessary to provide the appropriate drive speed for the accessories. Intermediate or transfer gearbox is used on some engines to obtain the needed reduction gearing. The more accessories an engine has the more power is needed to drive the gearbox.
  162. 162. ACCESSORY SECTION
  163. 163. ACCESSORY SECTION
  164. 164. ACCESSORY SECTION
  165. 165. ENGINE STATION NUMBERING       Engine manufacturers assign station number to several points along a turbine engine’s gas path. Station number provide a mean of rapidly locating certain engine areas during maintenance. Establish locations for taking pressure and temperature readings. Engine inlet pressure station is pt2 while turbine discharge pressure station is pt7. Engine pressure ratio is pt7 : pt2. Pt2 is total pressure at station 2 and Tt2 is total temperature at station 2.
  166. 166. ENGINE STATION NUMBERING
  167. 167. NOISE SUPPRESSION     Noise produced by a turbine engine results when hot, high velocity gases mix with cold, low velocity air surrounding the engine. Turbofan engines reduce the noise levels both inside the cabin and on ground . Turbofan engines seldom require noise suppressors because the hot gases mix with cold gas prior to their release to atmosphere. Turbojet engine require additional noise suppression equipment.
  168. 168. NOISE SUPPRESSION      A device that breaks up the airflow behind the tail cone and sound insulating material are used as noise suppressors. The sound intensity is measured in decibels. Decibel is the ratio of one sound to another. One decibel is the smallest change in sound intensity that the human ear can detect. FAA establish rules for aircraft operators that specify maximum noise levels.
  169. 169. NOISE SUPPRESSION
  170. 170. NOISE SUPPRESSION
  171. 171. ENGINE MOUNTS     Gas turbine engine relatively produce little torque so they do not need heavily constructed mounts. The mounts support the engine weight and allow for transfer of stresses created by the engine to the aircraft structure. Wing mounted turbofan engine, the engine is attached to the A/C by two to four mounting brackets. Turboprop and turboshaft engines use heaver mounts because of the torque developed.
  172. 172. ENGINE MOUNTS
  173. 173. BEARINGS      Engine main bearing support the compressor and turbine rotor, and located along the length of the rotor shaft. The number of bearing is determined by the length and weight of the rotor shaft. Spilt spool axial compressor require more main bearing than a centrifugal compressor. Ball and roller bearing are used to support an engine’s main rotor shaft. Consist of inner and outer races that provide support and hold lubricating oil.
  174. 174. BEARINGS  Advantages of ball and roller bearings: Offer little rotational resistance. 2.Enable precision alignment of rotating elements. 3.Tolerate high momentary overloads. 4.Are easily replaced. 5.Are relatively inexpensive. 6.Are simple to cool, lubricate, and maintain. 7.Accommodate both radial and axial loads. 8.Are relatively resistant to elevated temperatures. 1.
  175. 175. BEARINGS Disadvantages of ball and roller bearings: Vulnerability to damage caused by foreign matter. 2.Tendency to fail without appreciable warning. Proper lubrication and sealing against entry of foreign matter is essential. Labyrinth, helical thread, and carbon seal are used to seal the bearings from foreign matter. 1.
  176. 176. BEARINGS Labyrinth seal does not rub against an outer surface, instead each seal consist of a series of rotating fins that come very close but do not touch a fixed abradable race. Air pressure on one side prevent the oil from coming out of the bearing. Helical seals depend on reverse threading to stop oil leakage. Carbon seals are spring loaded to hold the carbon ring against the rotating shaft. 
  177. 177. BEARINGS
  178. 178. TURBOPROP ENGINES     Gas turbine engine that drives a propeller to produce thrust. The turbine of a turboprop engine extract up to 85% of the engine’s total power output to drive the propeller. Multiple stages turbine and special design blades to extract more energy from the exhaust gases. Most turboprop engines use a free turbine to drive the propeller.
  179. 179. TURBOPROP ENGINES      Free turbine is an independent turbine that is not mechanically connected to the main turbine. Power turbine is placed in the exhaust stream after the main turbine and dedicated to drive the propeller. Fixed shaft engines is used to extract the gas energy to drive the propeller by adding more turbine stages to the main shaft. High speed low torque turbine output is converted to low speed high torque by a reduction gear to drive the propeller. Constant speed propellers are used to maintain a constant engine rpm.
  180. 180. TURBOPROP ENGINES
  181. 181. TURBOSHAFT ENGINES      Gas turbine engine that operate something other than a propeller. Use almost all the energy in the exhaust gases to drive an output shaft. Power may be taken from the engine turbine or from a free turbine. Free turbine is not mechanically coupled to the main turbine and may operate at its own speed. Used to power helicopters and APUs.
  182. 182. AUXILIARY POWER UNITS     Turbine powered aircraft require large amounts of power for starting and operation. Electrical power is needed for passenger amenities such as lighting, entertainment, and food preparation. High pressure, high volume pneumatic air source is needed to start the engine and ground air conditioning. Auxiliary power units meet these demands for ground power when the engines are not running.
  183. 183. AUXILIARY POWER UNITS       Consist of a small turbine powerplant driving an electric generator identical to aircraft generators. APU compressor supplies bleed air for heating cooling, antiicing and engine starting. APU is started using its own electric starter motor and aircraft battery power using the fuel of the aircraft. APU fuel control unit automatically adjust the fuel flow to operate the APU at its rated speed. Load control valve protect the APU from overheating by modulate the pneumatic load automatically. Cool down period is specified by the manufacturer to keep the APU from being damaged because of thermal shock.
  184. 184. AUXILIARY POWER UNITS
  185. 185. OPERATING PRINCIPLES    Gas turbine engine is a heat engine that converts the chemical energy of fuel into heat energy. Heat energy is converted into kinetic energy in the form of a high velocity stream of air. The kinetic energy is converted into mechanical energy by the turbine that drive the compressor and the accessories and/or the propeller or gearbox.
  186. 186. ENERGY TRANSFORMATION CYCLE      Energy transformation cycle in a gas turbine engine is known as the Brayton or constant pressure cycle. Intake, compression, combustion, and exhaust event occur in both piston and turbine cycle. In turbine engine all four events happen simultaneously and continuously. Gas turbine engine produce power continuously. Gas turbine engine must burn a great deal of fuel to support the continuous production of power.
  187. 187. ENERGY TRANSFORMATION CYCLE
  188. 188. ENERGY TRANSFORMATION CYCLE        The air is continuously drawn into the engine thorough the inlet to the first compressor stage. The compressor increase the static air pressure of the air. Fuel is sprayed in the combustion chamber and ignited resulting in continuous combustion. The heat increase the air’s volume while maintaining a relatively constant pressure. Exhaust gases leave the combustion gases through the turbine where pressure decreases and the velocity increases dramatically. Gas turbine engine produces thrust based on Newton’s third law of motion. The acceleration of a mass of air by the engine is the action while forward movement is the reaction.
  189. 189. ENERGY TRANSFORMATION CYCLE   The working cycle upon which the gas turbine engine functions is represented by the cycle shown on the pressure volume diagram Point A represents air at atmospheric pressure that is compressed along the line AB. From B to C heat is added to the air by introducing and burning fuel at constant pressure, thereby considerably increasing the volume of air. Pressure losses in the combustion chambers are indicated by the drop between B and C. From C to D the gases resulting from combustion expand through the turbine and jet pipe back to atmosphere. During this part of the cycle, some of the energy in the expanding gases is turned into mechanical power by the turbine.
  190. 190. VELOCITY AND PRESSURE       Velocity and pressure of the air passing through a gas turbine engine must change to produce thrust. Pressure is increased in the compressor while velocity remains relatively constant. Gas velocity must be increased after combustion to rotate the turbine. Bernoulli’s principle stats that; when a fluid or gas is supplied at a constant flow rate through a duct, the sum of the potential, or pressure energy, and kinetic, or velocity energy is constant. The pressure and velocity of a mass of air flowing in a divergent or convergent duct must increase or decrease accordingly. (energy can not be created or destroyed) The temperature of the air will change too.
  191. 191. VELOCITY AND PRESSURE
  192. 192. THRUST CALCULATIONS Jet engine produces thrust by accelerating an air mass to a velocity higher than that of the incoming air.  Newton’s 2nd law of motion stats that force is proportional to the product of mass and acceleration or acceleration is directly proportional to force and inversely proportional to mass. F=MXA F = force. M = mass. A = acceleration. 
  193. 193. THRUST CALCULATIONS The acceleration of air mass through a gas turbine engine is the difference between the exiting jet exhaust and the intake air.  The acceleration must be compared to a constant. (gravitational constant = 32.2 f/sec²)  Applying this to the formula F = Ms (V2 – V1)/g F =force. Ms = mass airflow through the engine V2 =air velocity at the exhaust. V1 = forward velocity of the engine. g = acceleration of gravity which is 32.2 ft./sec². 
  194. 194. THRUST CALCULATIONS Example:  Given Ms = 50 pounds per sec. V1 = 0 feet per sec. V2 = 1,300 feet per sec. g = 32.2 ft./sec². F gross = Ms x (V2 – V1 )/g = 50 lb./sec x (1300 ft/sec. – 0 )/ 32.2 ft./sec². =65,000 lb ft./sec²/ 32.2 ft./sec². = 2,018.6 pounds 
  195. 195. THRUST CALCULATIONS Example 2:  Given Ms = 50 pounds per sec. V1 = 734 feet per sec. V2 = 1,300 feet per sec. g = 32.2 ft./sec². F net = Ms x (V2 – V1 )/g = 50 lb./sec x (1300 – 734)/ 32.2 ft./sec². =50 x 566 / 32.2. = 878.9 pounds net thrust.  Thrust can be increased by increasing mass flow of air or by increasing the exhaust velocity.  As the aircraft speed increase more air enters the engine resulting in an increase in exhaust velocity. 
  196. 196. THERMAL EFFICIENCY    1. 2. 3. Thermal efficiency is the ratio of the actual power an engine produces divided by the thermal energy in the fuel consumed. Gas turbine engine can operate with thermal efficiency as high as 50 % while the thermal efficiency of reciprocating engine is between 30 to 40 %. Factors which determine thermal efficiency: Turbine inlet temperature. Compression ratio. Component efficiency of the compressor and the turbine.
  197. 197. THERMAL EFFICIENCY      The higher a gas turbine engine raises the temperature of the incoming air, the more thrust the engine can produce,. The limiting factor to increasing the temperature of the air is the amount of heat the turbine section can withstand. The more a gas turbine engine compresses the incoming air, the more thrust the engine can produce. Engine with high compression ratio force more air into the engine, so more heat energy transferred to internal airflow thus increasing the thermal efficiency. Compressor and turbine efficiency directly impact the compression ratio of the engine which has a direct impact on the thermal efficiency.
  198. 198. THERMAL EFFICIENCY
  199. 199. FACTORS AFFECTING THRUST  FACTORS AFFECTING THRUST: 1. 2. 3. 4. 5. TEMPERATURE. ALTITUDE. AIRSPEED. ENGINE RPM. FAN EFFICIENCY.
  200. 200. FACTORS AFFECTING THRUST       TEMPERATURE The more dense the air passing through an engine is, the more thrust the engine can produce. Air density is inversely proportional to temperature, as outside temperature increases (OAT), air density decreases. As the density of the air entering a gas turbine engine decreases, engine thrust also decreases. Thrust augmentation system is used to compensate for the effect of hot weather on the amount of thrust. Water injection system inject water, or a mixture of water and alcohol into the compressor inlet or in the combustion chamber. Water will cool the air mass, allow more fuel to be burned, and increase the air mass to maintain air pressure in the engine.
  201. 201. FACTORS AFFECTING THRUST
  202. 202. FACTORS AFFECTING THRUST          ALTITUDE As altitude increases the air pressure drops. The pressure at 18,000 feet is about 7.34 psi. The pressure at 20,000 feet is about 6.75 psi. The pressure at 30,000 feet is about 4.36 psi. As altitude increases the temp. also decreases. The decrease in the temp. increases the air density which increase the thrust. But the drop in pressure has a greater effect on decreasing the thrust. At 36,000 the temp. stabilizes at -69.7 deg. F, so the density of air stop increasing. Long range jet aircraft find 36,000 feet an optimum altitude to fly.
  203. 203. FACTORS AFFECTING THRUST
  204. 204. FACTORS AFFECTING THRUST    AIRSPEED As forward airspeed increases, the air mass acceleration in the engine decreases, so less thrust is produced. As the aircraft speeds up, more air is forced into the engine (ram effect), results in an increase in air pressure within the engine, which produces more thrust. The result of the thrust reduced by increasing the airspeed and the thrust increased by ram effect is known as ram recovery.
  205. 205. FACTORS AFFECTING THRUST
  206. 206. FACTORS AFFECTING THRUST      ENGINE RPM Early engines had a linear relationship between compressor rpm and engine thrust. Engine power output could be set using an rpm gauge. Modern turbofan engines have a non-linear relationship between compressor rpm and thrust produced. Power is set using an engine pressure ratio EPR since thrust and EPR have more proportional relationship than thrust and rpm. At low engine speeds, large increases in rpm produce relatively small increase in thrust and vise versa.
  207. 207. FACTORS AFFECTING THRUST    ENGINE RPM Compressor aerodynamics limits engine rpm because the efficiency begins to drop when the blade tip speed reach the speed of sound. The longer the blade is, the higher the tip rotational speed. Large diameter compressors turn at a relatively slow rotational speed, while small diameter compressors could reach 50,000 rpm.
  208. 208. FACTORS AFFECTING THRUST    FAN EFFICIENCY The more efficient the fan is, the more thrust the engine can produce. Turbofan replaced turbojet engines on most transport and business jet aircraft. Turbofan is quieter and much more fuel economic.
  209. 209. QUESTIONS

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