Gas Turbine Engine Fundamentals
1. Introduction to Gas Turbine Engines
1.1 Brayton Cycle
The Brayton cycle is a continuous combustion cycle.
1.2 Jet Engines vs. Rocket Engines
Rocket Engines:
- Carry their own fuel and oxidizer.
- Do not require atmospheric air for combustion.
Jet Engines:
- Use atmospheric air for combustion.
- Share the same principle of operation as rocket engines (action/reaction).
Key Difference: The primary difference lies in the source of the oxidizer.
1.3 Jet Engine and Turbofan Engine Characteristics
True Statement: The thrust delivered by jet and turbofan engines is less at high altitudes than at low altitudes.
1.4 Engine Efficiency
The basic parameter for describing engine efficiency is specific fuel consumption.
1.5 Bypass Ratio (BPR)
Bypass ratio (BPR) is the ratio between the mass of air that bypasses the combustion chamber and the mass of air that passes through it.
2. Engine Components and Operation
2.1 Thrust Generation
A jet engine generates thrust through the action/reaction principle applied to exhaust gases.
2.2 Turbine Stage Function
The primary purpose of the turbine stage in a gas turbine engine is to extract energy from the expanding gases, providing the power to drive the compressor and other engine accessories.
2.3 Exhaust Section
The exhaust section of a turbojet or turbofan engine is typically convergent, designed to increase the velocity of exhaust gases and decrease their pressure.
2.4 Thrust Augmentation
Methods to increase engine thrust include:
- Increasing the mass flow rate of air through the engine.
- Increasing the velocity of exhaust gases.
2.5 Engine Efficiency Comparison
A common method for comparing engine efficiencies is by evaluating the thrust-to-weight ratio.
2.6 Static Thrust
Static thrust is the thrust produced when the aircraft is stationary on the ground.
2.7 Thrust and RPM During Climb
In an aircraft without a Full Authority Digital Engine Control (FADEC) system, as the aircraft climbs with a fixed throttle position:
- Thrust decreases due to reduced air density.
- RPM increases to compensate for the reduced thrust.
2.8 Ram Effect
The ram effect, caused by the aircraft’s forward speed, compresses the incoming air, leading to increased air density. However, this effect generally decreases engine efficiency.
2.9 FADEC and Fuel Control
In gas turbine engines equipped with FADEC, the fuel flow is automatically adjusted to maintain the selected RPM as the aircraft climbs. This ensures optimal engine performance and fuel efficiency.
2.10 Engine Trimming
Engine trimming is typically performed under specific conditions, such as calm winds and low humidity, to optimize engine performance and fuel efficiency.
2.11 Flat Rating
Flat-rated thrust refers to the guaranteed thrust performance provided by the manufacturer for specific operating conditions, such as takeoff. This rating ensures consistent engine performance within defined limits.
2.12 Engine Pressure Ratio (EPR)
EPR is a crucial parameter indicating the thrust produced by the engine. It represents the ratio of the exhaust gas pressure to the intake air pressure.
3. Air Intake System
3.1 Intake Air Turbulence
Intake air turbulence negatively impacts compressor efficiency, reducing its ability to compress air effectively.
3.2 Intake Design
Intakes are designed to decelerate the free air stream flow, preparing it for entry into the compressor.
3.3 Intake Shape
The shape of a jet engine air intake is typically divergent, gradually increasing the cross-sectional area to reduce air velocity and increase pressure.
3.4 Abradable Lining
An abradable lining around the fan is employed to minimize the negative effects of fan blade tip losses, enhancing engine power and efficiency.
4. Compressor Section
4.1 Centrifugal Compressors
Centrifugal (radial) flow compressors are capable of achieving high compressor pressure ratios per stage, typically in the range of 8:1. They consist of two primary functional elements: the impeller and the diffuser.
- Impeller: Accelerates the air radially outward.
- Diffuser: Converts the high-velocity air into high-pressure air.
Advantages of centrifugal compressors include their high pressure rise per stage, simple design, and robust construction.
4.2 Axial Flow Compressors
Axial flow compressors offer good efficiency over a wide range of speeds. They consist of alternating rows of rotating blades (rotors) and stationary blades (stators).
- Rotors: Impart velocity to the air and increase its pressure.
- Stators: Guide the airflow to the next stage of rotors, preparing it for further compression.
Advantages of axial flow compressors include their high efficiency, compact design, and ability to handle large volumes of air.
4.3 Dual Axial Flow Compressors
Dual axial flow compressors enhance engine performance by efficiently compressing the air before it enters the combustion chamber. This is achieved through multiple stages of compression, resulting in a higher overall pressure ratio.
4.4 Compressor Speed Designation
In twin-spool engines, the speed of the low-pressure (LP) compressor is commonly designated as N1.
4.5 Compressor Stator Function
Compressor stators play a crucial role in guiding and slowing down the airflow, increasing its pressure. They direct the air into the rotor blades at the optimal angle for efficient compression.
4.6 Variable Inlet Guide Vanes (VIGVs)
VIGVs are adjustable vanes located at the compressor inlet. They direct the airflow to the first rotor stage at the proper angle, optimizing compressor efficiency across a range of engine speeds.
4.7 Compressor Surge and Stall
Compressor surge is an aerodynamic instability characterized by violent fluctuations in airflow and pressure within the compressor. It occurs when the compressor is unable to overcome the backpressure from the downstream components.
Compressor stall is a localized flow separation that occurs when the angle of attack of the airfoils exceeds a critical value. This disrupts the smooth airflow through the compressor, reducing its efficiency.
5. Combustion Section
5.1 Combustion Process
The combustion process in a gas turbine engine involves the rapid mixing and burning of fuel and air. Key factors influencing combustion efficiency include:
- Air pressure
- Fuel-air ratio
- Combustion chamber design
5.2 Secondary Air Flow
Secondary air flow in the combustion chamber plays a vital role in cooling the combustion liner and diluting the hot combustion gases. It flows between the outer casing and the inner liner, protecting these components from excessive heat.
5.3 Combustion Chamber Temperature
The flame temperature within the combustion chamber can reach extremely high levels, typically around 2000°C (3632°F). This intense heat necessitates the use of specialized materials and cooling techniques to ensure the integrity of the combustion chamber components.
5.4 Fuel Flow Divider
Fuel flow dividers are employed in combustion systems utilizing duplex nozzles. These dividers ensure an even distribution of fuel to the multiple nozzles, promoting efficient and uniform combustion.
5.5 Thermally Loaded Components
The combustion liner and turbine inlet guide vanes are subjected to the highest thermal loads within the engine. These components require specialized materials and cooling methods to withstand the extreme temperatures encountered during operation.
5.6 Swirl Vanes
Swirl vanes are strategically positioned within the combustion chamber to enhance the mixing of air and fuel. This swirling motion promotes efficient combustion and reduces the formation of pollutants.
6. Turbine Section
6.1 Temperature Drop
As the hot gases expand through the turbine stages, their temperature gradually decreases. This temperature drop is a fundamental aspect of the energy conversion process within the turbine.
6.2 Turbine Inlet Nozzles
Turbine inlet nozzles are responsible for converting the pressure and heat energy of the hot gases into kinetic energy, accelerating the gas flow before it encounters the turbine blades.
6.3 Turbine Stage Definition
A turbine stage comprises a set of stationary turbine inlet guide vanes and a row of rotating turbine blades. These components work together to extract energy from the expanding gases and convert it into rotational mechanical energy.
6.4 Turbine Function
The primary function of the turbine is to provide the necessary torque to drive the compressor, fan, and other engine accessories. It accomplishes this by extracting energy from the expanding gases and converting it into rotational mechanical energy.
6.5 Turbine Shaft Material
Turbine shafts are typically manufactured from high-strength steel alloys capable of withstanding the extreme temperatures, centrifugal forces, and torsional stresses encountered during operation.
6.6 Turbine Blade Installation
Turbine blades can be installed using various methods, including fir-tree and rivet attachment techniques. The chosen method depends on factors such as engine design, blade material, and operating conditions.
6.7 Turbine Blade Clearance
The clearance between turbine blades is minimized during engine operation when the components are hot. This tight clearance is crucial for maximizing turbine efficiency by reducing gas leakage between the blades.
6.8 Turbine Cooling System
Turbine cooling systems utilize air bled from the high-pressure compressor to cool the turbine blades and vanes. This cooling air is directed through internal passages within these components, reducing their operating temperatures and extending their lifespan.
6.9 Shrouded Turbine
In a shrouded turbine, the tips of the turbine blades are connected by a shroud, forming a continuous ring. This design feature enhances aerodynamic efficiency and structural integrity, particularly at high rotational speeds.
6.10 Convection Cooling
Convection cooling is a method of cooling turbine blades and vanes by passing a stream of cooling air over their surfaces. This airflow removes heat from the components, reducing their operating temperatures.
6.11 Multiple Turbine Stages
Some turbine engines incorporate multiple turbine stages to extract more power from the exhaust gases than a single stage could achieve. This multi-stage design enhances overall engine efficiency and power output.
6.12 Turbine Blade Creep
Turbine blade creep is a time-dependent deformation that occurs in turbine blades subjected to high temperatures and centrifugal forces. This phenomenon can lead to blade failure if not adequately addressed through material selection and design considerations.
7. Exhaust Section
7.1 Jet Nozzle Location
The jet nozzle is located in the exhaust section of a turbojet engine, downstream of the turbine.
7.2 Exhaust Cone Assembly
The exhaust cone assembly in a turbine engine serves to straighten and collect the exhaust gases, directing them rearward to produce thrust.
7.3 Reverse Thrust
Full reverse thrust is typically around 50% of the forward thrust. It is used to decelerate the aircraft during landing or to back it up on the ground.
7.4 Convergent Nozzle
The purpose of a convergent nozzle is to increase the velocity of subsonic airflow while reducing its pressure. This principle is applied in the exhaust nozzle of a jet engine to accelerate the exhaust gases and generate thrust.
7.5 Thrust Reverse System
Thrust lever for thrust reverse system deployment are typically located on the throttle levers in the cockpit.
7.6 Engine Noise Generation
A significant portion of engine noise is generated when the high-velocity, turbulent exhaust gases mix with the relatively still surrounding air. This interaction creates pressure waves that propagate as sound.
7.7 Carbon Monoxide Reduction
Higher combustion temperatures in the engine help minimize the formation of carbon monoxide (CO) in the exhaust gases. This is because complete combustion, which reduces CO emissions, is favored at higher temperatures.
7.8 NOx Formation
The formation of nitrogen oxides (NOx) increases with higher combustion temperatures. NOx emissions are a significant environmental concern associated with gas turbine engines.
8. Lubrication System
8.1 Turbine Bearing Temperature
The highest turbine bearing temperatures typically occur during engine shutdown. This is due to the loss of cooling airflow as the engine stops running.
8.2 Bearing Seal Failure
Bearing seal failure often leads to increased oil consumption. This is because the failed seals allow oil to escape from the lubrication system.
8.3 Pressurized Oil Seals
Oil seals are pressurized to minimize oil loss from the lubrication system. This pressure helps prevent oil from leaking past the seals.
8.4 Oil Seal Types
Common types of oil seals used in turbine engines include labyrinth seals and carbon seals. These seals are designed to withstand the high temperatures, pressures, and rotational speeds encountered in these demanding applications.
8.5 Hydraulic Bearing Advantages
One of the most significant advantages of hydraulic bearings is their ability to operate with a thin film of oil, which is continuously supplied under pressure. This lubrication method reduces friction, wear, and heat generation, contributing to improved bearing life and reliability.
9. Fuel System
9.1 Kerosene Production
Kerosene is a product of fractional distillation of petroleum. It is a middle distillate, heavier than gasoline but lighter than diesel fuel.
9.2 Kerosene Source
Kerosene is derived from the kerosene fraction of petroleum distillation. This fraction boils at a temperature range between gasoline and diesel fuel.
9.3 Microbial Growth
Microbes are more likely to thrive in areas where fuel and water can accumulate and stagnate. These conditions provide a favorable environment for microbial growth, which can lead to fuel contamination and corrosion.
9.4 Oil Filter Bypass
If an oil filter becomes completely clogged, oil will bypass the filter element through a bypass valve. This ensures continued oil flow to the engine, preventing oil starvation, but the oil will not be filtered, potentially leading to increased wear and tear on engine components.
9.5 High-Pressure Oil Filter
The main high-pressure filter in a gas turbine lubrication system is primarily intended to protect downstream components, such as bearings and seals, from contaminants that may be present in the oil.
9.6 Oil Heat Pickup
Oil picks up the most heat from the turbine bearings. This is because bearings generate significant heat due to friction.
10. Fuel Control System
10.1 Duplex Burner Outlets
Duplex burners typically have two calibrated outlets: a primary outlet and a secondary outlet. These outlets allow for precise fuel metering and control over a wide range of engine operating conditions.
10.2 Hydromechanical/Electronic Fuel Control
In a hydromechanical/electronic dual-control fuel system, the filter bypass valve is open during engine start to ensure a constant fuel flow. This bypass mechanism allows the engine to receive fuel even if the filter is cold and partially clogged.
10.3 Fuel Flow During Start
During the engine start sequence, only the primary flow from the fuel divider is open. This initial fuel flow is carefully metered to ensure a smooth and controlled engine start.
10.4 Secondary Fuel Flow
At maximum engine speed, the secondary flow through the duplex nozzle is approximately 90% of the total fuel flow. This high proportion of secondary flow contributes to achieving maximum thrust.
10.5 Electronic Engine Control (EEC) Cooling
The EEC is typically cooled by convection, utilizing airflow to dissipate heat generated by its electronic components.
10.6 EEC Thrust Control Modes
The EEC can control engine thrust in two primary modes:
- Primary Mode (EPR): Maintains a constant engine pressure ratio (EPR).
- Secondary Mode (N1): Maintains a constant low-pressure compressor speed (N1).
10.7 Fuel Management Unit (FMU)
The FMU is typically installed on the front face of the engine gearbox. It is a critical component of the fuel control system, responsible for metering and controlling the flow of fuel to the engine.
10.8 Low-Pressure (LP) Fuel Pump
The purpose of the LP fuel pump stage is to boost fuel pressure before it reaches the high-pressure (HP) fuel pump. This pre-boosting stage prevents cavitation in the HP pump, ensuring a consistent and reliable fuel supply.
10.9 Engine-Driven Fuel Pump Location
The main engine-driven fuel pump is typically located on the accessory gearbox. This gearbox is driven by the engine, providing mechanical power to various engine accessories, including the fuel pump.
10.10 Fuel Pump Pressure Relief Valve
The pressure relief valve in an engine fuel pump is designed to return excess fuel to the pump inlet if the pressure exceeds a predetermined limit. This safety mechanism protects the fuel system from damage due to overpressure.
10.11 Fuel Pump Design
Fuel pumps in gas turbine engines are commonly designed as positive displacement pumps. These pumps deliver a fixed volume of fuel per revolution, regardless of the discharge pressure.
10.12 Fuel Filter Types
Gas turbine engines typically employ two main types of fuel filters:
- Low-Pressure Filter: Utilizes a paper filter element for initial fuel filtration.
- High-Pressure Filter: Employs a wire mesh filter element for finer fuel filtration.
10.13 Duplex Nozzle Operation
A duplex nozzle utilizes both the primary and secondary burners at both low and high RPM. This dual-burner design allows for efficient combustion and thrust generation across a wide range of engine operating conditions.
10.14 Combustion Chamber Drain
The combustion chamber drain serves to collect and remove any fuel that may accumulate in the combustion chamber after engine shutdown or a false start. This prevents fuel from pooling in the combustion chamber, which could pose a fire hazard.
11. Engine Cooling and Bleed Air System
11.1 High-Pressure Turbine (HPT) Inlet Guide Vane (IGV) Cooling
HPT IGVs are cooled by air bled from the low-pressure compressor (LPC). This cooling air helps reduce the thermal stresses on the IGVs, extending their lifespan.
11.2 Bleed Air and EGT
When air is bled off the engine for purposes such as anti-icing, the exhaust gas temperature (EGT) will typically increase. This is because the bleed air is no longer available for cooling the engine components, leading to a rise in EGT.
11.3 Engine Zones
Engine zones are designated areas within the engine based on their temperature and potential fire hazards. Zone 1 typically refers to the fan case zone, which is relatively cool compared to other areas.
11.4 Hottest Engine Area
The hottest area inside the engine is typically around the HPT. This is where the combustion gases reach their highest temperatures.
11.5 EEC Location
The EEC is typically located in Zone 1 of the engine, which is a relatively cool and protected area.
11.6 Combustion Liner Cooling Air Source
The air for cooling the combustion liners is primarily supplied from the secondary air flow. This flow of cooler air helps regulate the temperature of the combustion liners, preventing overheating and damage.
11.7 Pressure Relief Door Location
The pressure relief door is typically located in Zone 1 of the engine. This door acts as a safety device, opening to relieve excessive pressure within the engine if necessary.
11.8 Engine Section Terminology
The forward part of the engine, encompassing the air intake and compressor sections, is often referred to as the”cold section” Conversely, the aft part of the engine, including the combustion and turbine sections, is known as the”hot section”
11.9 Ideal Air/Fuel Ratio
The ideal air/fuel ratio for complete combustion in a gas turbine engine is approximately 15:1. This means that 15 parts of air are required for every 1 part of fuel to ensure efficient combustion.
11.10 Ventilation Air Exit
Air used for ventilation purposes within the engine typically exits the engine in the intake area. This ventilation airflow helps prevent the buildup of heat and fumes in these areas.
11.11 Engine Anti-Ice Bleed Air Source
Engine anti-ice systems commonly utilize bleed air taken from the high-pressure compressor. This hot, pressurized air is ducted to critical areas, such as the engine inlets and fan blades, to prevent ice formation.
11.12 Anti-Icing Method
Anti-icing of jet engine air inlets is typically accomplished by ducting engine bleed air through critical areas prone to ice formation. This hot air prevents ice from accumulating on these surfaces, ensuring proper engine operation.
12. Starting System
12.1 Starting Sequence
During the starting sequence of a fan gas engine, ignition typically occurs after fuel injection. This sequence ensures that fuel is present in the combustion chamber before the ignition system is activated.
12.2 High-Energy Ignition Requirements
Turbine engines require high-energy ignition systems to ignite the fuel-air mixture under challenging conditions, such as high altitudes and low temperatures. These conditions make ignition more difficult, necessitating a robust ignition system.
12.3 Ignition System Shielding
Shielding is employed on spark plugs and ignition leads to prevent electromagnetic interference with radio reception and other sensitive electronic equipment on the aircraft.
12.4 Igniter Plug Removal
When removing a turbine engine igniter plug, it is standard practice to first disconnect the igniter leads from the plug. This precaution prevents accidental damage to the ignition system.
13. Engine Instrumentation
13.1 EGT Gauge Power
EGT (Exhaust Gas Temperature) gauges typically require 115VAC power for operation.
13.2 Thermocouple Temperature Sensing
In a thermocouple temperature sensing system, a cold junction compensates for varying ambient temperatures at the hot junction. This compensation ensures accurate temperature measurements.
13.3 Thrust Indication
Thrust in a high-bypass fan engine is commonly indicated by engine pressure ratio (EPR) or N1 (low-pressure compressor) RPM.
13.4 Engine Pressure Ratio (EPR)
Engine pressure ratio (EPR) is a measure of the ratio of exhaust gas pressure to intake air pressure. It serves as an indicator of the thrust produced by the engine.
13.5 Gas Turbine Tachometer Calibration
Gas turbine tachometers are typically calibrated in percent of engine RPM. This allows for a standardized indication of engine speed, regardless of the specific engine type or model.
13.6 Fuel Flow Transmitter
The fuel flow transmitter is responsible for measuring and transmitting fuel flow data. It often incorporates a counter to track the total amount of fuel consumed.
13.7 Fuel Flow Measurement Units
Fuel flow in aircraft engines is commonly measured in kilograms per hour (kg/h). This unit provides a standardized way to quantify fuel consumption.
13.8 Oil Pressure Indication
Oil pressure indication typically represents the absolute pressure in the oil pressure supply line. This pressure reading provides insights into the health and performance of the engine lubrication system.
13.9 Engine Oil Temperature Measurement
Engine oil temperature is typically measured at the inlet to the oil tank or within the oil tank itself. This temperature reading helps monitor the oil’s operating temperature and assess its condition.
14. Thrust Augmentation Systems
14.1 Afterburning System
Afterburning systems are primarily used on some low-bypass engines to provide a significant increase in thrust for short periods, typically during takeoff or combat maneuvers. They work by injecting fuel into the exhaust stream, where it ignites and burns, generating additional thrust.
14.2 Afterburner Temperature
When an afterburner system is activated, the temperature in the exhaust nozzle increases significantly. This is because the afterburner injects and burns additional fuel in the exhaust stream, raising the temperature of the exhaust gases.
14.3 Water Injection System
Water injection systems inject water into the compressor inlet or diffuser case. This water mist evaporates, cooling the air and increasing its density, which allows the engine to produce more thrust, particularly in hot weather conditions.
14.4 Water-Methanol Injection
As an alternative to water injection, some systems use a mixture of water and methanol. Methanol, being more volatile than water, evaporates more readily, further enhancing the cooling and thrust-boosting effects.
14.5 Water Injection Thrust Increase
Water injection increases thrust by increasing the density of the air entering the engine. Cooler, denser air allows the engine to burn more fuel and produce more power.
15. Turboprop and Turboshaft Engines
15.1 Free Turbine Engines
Free turbine engines feature two separate shafts: one driving the compressor and the other driving the propeller. This design allows the propeller to operate at its optimal speed, independent of the compressor speed.
15.2 Propeller Control
Propeller controls for flight operations typically manage both the pitch angle of the propeller blades and the fuel flow to the engine. This coordinated control system, often referred to as”alpha range” optimizes propeller efficiency and engine performance.
15.3 Turboshaft Engine Reduction Gear
Reduction gears in helicopter turboshaft engines serve to reduce the high rotational speed of the turbine to a lower speed suitable for driving the helicopter’s rotor system. This speed reduction is essential for efficient rotor operation.
15.4 Turboshaft Engine RPM Relationship
In turboshaft engines, the N1 (gas generator speed) and N2 (power turbine speed) are interdependent. Changes in N1 RPM directly influence N2 RPM, and vice versa.
16. Auxiliary Power Unit (APU)
16.1 APU Peak Load
The APU experiences its greatest load when bleed air is extracted for aircraft systems and the generator is supplying electrical power. These combined demands place a significant load on the APU.
16.2 APU Generator
The electrical generator on an aircraft’s APU is often identical or very similar to the engine-driven generators. This commonality simplifies maintenance and reduces the need for specialized parts.
16.3 APU Bleed Air Load
A significant portion of the load on an APU often arises from the demand for bleed air. Bleed air is used for various purposes, including cabin pressurization, air conditioning, and engine starting.
17. Fire Protection System
17.1 Dual-Loop Fire Detection
Dual-loop fire detection systems provide redundancy in fire detection. Both loops must detect a fire for a warning indication to be triggered, reducing the likelihood of false alarms.
17.2 Fire Detection Control Unit
The control logic for the fire detection system is housed within the fire detection control unit. This unit processes signals from the fire detection loops and initiates appropriate actions in case of a fire.
17.3 Engine Fire Response
In the event of an engine fire, the standard response is to shut down the affected engine and isolate its fuel, hydraulic, electrical, and pneumatic systems. This isolation helps prevent the fire from spreading to other parts of the aircraft.
17.4 Engine Isolation
Engines are typically isolated in case of fire by closing the fuel management unit (FMU) cutoff valve. This action stops the flow of fuel to the engine, starving the fire.
18. Engine Maintenance and Inspection
18.1 Wet Engine
The term”wet engin” typically refers to motoring the engine using the starter without igniting the fuel. This procedure is often performed during maintenance to lubricate engine components or to check for mechanical issues.
18.2 Turbine Blade Blowing
Blowing of turbine blades, a condition where the tips of the blades rub against the engine casing, often indicates an improper engine cool-down period was not observed. Allowing the engine to cool down gradually after operation is crucial to prevent this type of damage.
18.3 Blade Moment-Weight Information
Information regarding the moment-weight of a turbine blade can often be found on the rear face of the blade’s fir-tree root attachment. This information is essential for balancing the engine rotor assembly.
18.4 Metal in Oil Analysis
Spectrometric oil analysis is a technique used to determine the type and quantity of metal particles present in engine oil. This analysis helps identify wear patterns and potential component failures.
18.5 Compressor Blade Inspection
Repaired compressor blades are typically inspected using either magnetic particle inspection or fluorescent penetrant inspection. These nondestructive testing methods help detect surface cracks or defects in the blades.
18.6 Turbine Disk Clearance
The running clearance between the turbine disk and the engine casing is kept to a minimum to reduce aerodynamic losses, known as tip losses. This tight clearance enhances turbine efficiency.
18.7 Silica Gel Use
Silica gel is a desiccant used to absorb moisture from the air. It is often placed inside engines during storage to prevent corrosion.
18.8 Gas Loads on Engine
Gas loads acting on the forward part of the engine, such as those generated by the compressor, are directed forward. These loads must be accounted for in the engine’s design and mounting.
18.9 Secondary Air Flow Source
Secondary air flow, used for cooling various engine components, is typically supplied from the low-pressure compressor (LPC). This bleed air is ducted to specific locations within the engine to regulate temperatures and prevent overheating.