POWERPLANT

For every force acting on a body, there is an opposite and equal reaction

Newton’s 3rd Law of Motion

4 Forces acting in a Flight

Drag

Lift

Weight

Thrust

By taking in a quantity of air and accelerating it through an orifice or nozzle. The acceleration of the air is the action and forward movement is the reaction.

How jet propulsion apply 3rd law of motion

Newton’s 2nd Law of Motion

"Force equals mass accelerated

increase the speed of exhaust gases

increase quantity of exhaust gases

Jet engine thrust can be increased in two ways

Hero, 250 BC

devised a toy that used the reaction principle

Da Vinci, 1500 BC

described the chimney jack, as the hot air from the fire rose, it was made to pass through a series of fan blades and through a series of gears, turn a roasting

Dr. Sanford Moss, 1900

He applied some of his concepts in the development of the turbo-supercharger.

Frank Whittle 1930

developed what became the first successful turbojet engine and was granted his first patent for the jet engine

Gloster model E28/39 aircraft

Frank Whittle’s engine completed its first flight in a ______

jet propulsion

The majority of commercial aircraft utilize some form of _____.

Air Breathing

Uses atmospheric air (+ some fuel) as main propellant

Piston

Gas Turbine

Ramjet Engines

Examples of Air Breathing

• Air enters the through the intake duct (cowl).

• Air compressed by passage through the compressor.

• Mixed with fuel in the combustion chamber.

• Fuel is ignited, Pressure and Temperature raised

• Some of the pressure used to turn a turbine;

• Turbine shaft drives the compressor.

• Hot, high pressure air forced through a nozzle.

• The reaction force is the engine thrust

Jet Engine Basic Operation

Ram Jet

Pulse Jet

Scram Jet

Rocket Engine

Gas Turbine Engine

Types of Jet Engines

Aero-thermodynamic-duct (athodyd)

has no rotating parts and consists of a duct with a divergent entry and a convergent or convergentdivergent exit.

Ram Jet

With a forward motion imparted by an external source, air is forced in the divergent inlet (increasing its pressure) the total energy of air is further increased by combustion of fuel and the rapid expanding gases accelerate to the atmosphere through the outlet duct.

Pulse Jet

Can be run at static conditions unlike the ram jet and is constructed with a robust construction

Scram Jet

a variant of a ramjet air breathing jet engine in which combustion takes place in supersonic airflow.

Rocket Engine

A jet engine that does not use atmospheric air as a propulsive fluid stream (non-air breathing)

Gas Turbine Engine

the most practical form of jet engine in use today. It has become the standard on nearly all transport category, business, and military aircraft. Works in the same manner as a reciprocating engine but all events happen simultaneously.

Turbo jet

Air is compressed in the compressor, burned in the combustion chamber, expands and spins the turbine which in turn drives the compressor (selfsustaining), and leaves the exhaust at high velocities.

Engine Pressure Ratio

the ratio of turbine discharge pressure to the inlet air pressure

Turboprop

A gas turbine engine that delivers power to a propeller

Turboprop

Reduction gearing is necessary because optimum propeller performance is achieved at much slower speeds than the engine's operating rpm.

Turboshaft

A gas turbine engine that delivers power to a shaft that can drive something else is referred to as a turboshaft engine.

Turboshaft

used as auxiliary power units and in industrial applications to drive electrical generators and surface transportation systems.

Turbofan

consists of a multibladed ducted propeller driven by a gas turbine engine.

Turbofan

have turbojet-type cruise speed capability, yet retain some of the short-field takeoff capability of a turboprop

forward-fan engines

Engines that have the fan mounted in front of the compressor are called

aft-fan engines

turbofan engines that have the fan mounted to the turbine section are called

Bypass ratio

Bypass air to engine air

Thrust ratio

fan to engine core exhaust

Fan pressure ratio

Pressure leaving the fan to pressure entering the fan

Air Inlet

The first major section of a turbine engine. It is one of the cold sections of turbine engine.

Ram recovery or pressure recovery

Recover as much of the total pressure of the free airstream as possible and deliver this pressure to the compressor.

Velocity - decreasing

Pressure - increasing

Temperature - increasing

Divergent Duct =<

Velocity - increasing

Pressure - decreasing

Temperature - decreasing

Convergent Duct =>

Engine Mounted - DC-10 and L-1011

Wings Mounted - Havilland Comet and de Havilland Vampire

Fuselage Mounted - Dassault Super Mystere

Subsonic Inlet

Supersonic Inlet

Bellmouth Inlet

\

Types of Air Inlet Ducts

Subsonic Inlet

consists of a fixed geometry duct whose diameter progressively increases from front to back. This divergent shape works like a venturi in that as the intake air spreads out, the velocity of the air decreases and the pressure increases.

Supersonic Inlet

has either a fixed or variable geometry whose diameter progressively decreases, then increases from front to back. This convergent-divergent shape is used to slow the incoming airflow to subsonic speed before it reaches the compressor.

Bellmouth Inlet

These have a convergent profile that is designed specifically for obtaining very high aerodynamic efficiency when stationary or in slow flight.

Compressor Section

The second major section and also a part of the cold section of a gas turbine engine. It is the component that forces air into the engine. Its main objective is to supply compressed air for combustion in the combustion chamber.

Compression Pressure Ratio

This ratio is the outlet pressure divided by the inlet pressure.

20 to 30 times, 400 to 500 ft/s

To be effective, a modern compressor must increase the intake air pressure ___to ________ times above the ambient air pressure and move the air at a velocity of __ to _ feet per second

Compressor

supply bleed air/customer bleed air for various purposes in the engine and aircraft.

1\. Cabin pressurization, heating, and cooling;

2\. De-icing and anti-icing equipment;

3\. Pneumatic starting of engines

current applications of bleed air are:

Centrifugal Flow and Axial Flow

Compressor Section Types

Centrifugal Flow - Impeller (rotor), Diffuser, Manifold

Sometimes called a radial outflow compressor. This type of compressor is one of the earliest compressor designs and is still used today in some smaller engines and auxiliary power units (APU’s).

Impeller

consists of a forged disk with integral blades fastened by a splined coupling to a common power shaft. Its function is to take air in and accelerate it outward by centrifugal force

Double-sided impeller

When two impellers are mounted back-to-back

Impeller - air is expelled into divergent duct called diffuser

Diffuser - air spreads out, slows down, and increases static pressure

Manifold - distributes air in smooth flow to combustion section

Process of compressor section

Simple to manufacture

Low cost

Low weight

Low starting power requirements

Operating efficiency

Advantage of Centrifugal Flow Compressor

large frontal area, increases aerodynamic drag

practical limits on the number of stages

disadvantage of centrifugal flow compressor

Axial Flow

airflow is along the horizontal axis of the compressor. It raise air pressure rather than air velocity.

stainless steel, titanium

The rotor blades are usually made of ____ with the latter stages being made of ___________

stator vanes

arranged in fixed rows between the rows of rotor blades and act as diffusers at each stage, decreasing air velocity and raising pressure.

Inlet Guide Vanes

The set of stator vanes immediately in front of the first stage rotor blades. These vanes direct the airflow into the first stage rotor blades at the best angle while imparting a swirling motion in the direction of engine rotation.

Outlet Guide Vanes

The last set of vanes the compressor air passes through. These vanes straighten the airflow and eliminate any swirling motion

High peak efficiencies

Small frontal area

straight through flow

increases pressure rise by increasing number of stages

Axial Flow advantages

good efficiency over only narrow rotational speed range

difficult to manufacture

high cost

high weight

high starting power requirement

Axial Flow disadvantages

Compressor Stall

occurs when the compressor blades' angle of attack exceeds the critical angle of attack

Hung stalls

are severe stalls that can significantly impair engine performance, cause loss of power, and can damage the engine

Combustion Section

typically located directly between the compressor diffuser and turbine section.

Fuel Injection System

meters the appropriate amount of fuel through the fuel nozzles into the combustors

Ignition Source

the highenergy capacitor discharge system, consisting of an exciter unit, two high-tension cables, and two spark igniters. This ignition system produces 60 to 100 sparks per minute, resulting in a ball of fire at the igniter electrodes.

Fuel Drainage System

accomplishes the important task of draining the unburned fuel after engine shutdown.

Combustion Chamber (combustors)

where the fuel and air are mixed and burned.

Tubular

series of individual combustor cans which act as individual burner units. multiple can combustors can be individually removed for inspection

Annular Type

consists of a housing and perforated inner liner, or basket. It must be removed as a single unit for repair or replacement. commonly used in both small and large engines.

Can-annular type

represent a combination of the multiple-can combustor and the annular type combustor. It was invented by Pratt & Whitney and consists of a removable steel shroud that encircles the entire combustion section. individual can and liner is removed and installed as one unit for maintenance

25 to 35 percent of the incoming air

Designated as primary air

65 to 75 percent

Designated as secondary air

500 ft/s

Air from the engine compressor enters the combustion chamber at a velocity up to ____ feet per second, which is then diffused (decelerate velocity) and raised its static pressure.

45:1 and 130:1

In normal operation, the overall air/fuel ratio of a combustion chamber can vary between ________.

20

Approximately ----per cent of the air mass flow is taken in by the snout or entry section. Selected number of secondary holes through which a further ----- percent of the main flow of air passes into the primary zone

Turbine

transforms a portion of the kinetic energy in the hot exhaust gases into mechanical energy to drive the compressor and accessories.

Turbine Case

encloses the turbine rotor and stator assembly, giving either direct or indirect sup-port to the stator elements

Turbine Stator

most commonly referred to as the turbine nozzle, turbine guide vanes, or the nozzle diaphragm.

Turbine Stator

Collects the high energy airflow from the combustors and direct the flow to strike the turbine rotor at the appropriate angle.

Shroud

retains and surrounds the nozzle vanes

Turbine Rotor

a dynamically balanced unit consisting of blades attached to a rotating disk.

Turbine Disk

the anchoring component for the turbine blades and is bolted or welded to the main shaft

Growth or Creep

a phenomena in which extreme stress on turbine blades may cause the turbine blades to grow in length due to severe centrifugal loads imposed by high rotational speeds.

Turbine Blades

airfoil shaped components designed to extract the maximum amount of energy from the flow of hot gases.

Impulse Turbine Blades

the blades merely change the direction of airflow coming from the turbine nozzle and cause relatively no change in gas pressure or velocity

Reaction Turbine Blades

produce a turning force based on an aerodynamic action.

Impulse-reaction turbine blades

the workload along the length of the blade is evenly distributed. The blade base is impulse shaped while the blade tip is reaction shaped. Made to evenly distribute the workload along the length of the blade.

Shroud

attached to the tips of the turbine blades to reduce vibration

Convection Cooling/Film Cooling

compressor bleed air is typically directed in through the hollow blades and out through holes in the tip, leading edge, and trailing edge.

Transpiration Cooling

used on stationary nozzle vanes, bleed air is ducted into the vanes and exits through the porous material

Active Tip Clearance Control

controls the thermal expansion rate of the turbine case by regulating the flow of cooling air around the turbine case

Transpiration Cooling

only used on stationary nozzle vanes, bleed air is ducted into the vanes and exits through the porous material

Counter Rotating Turbines

chosen by engine designers for their effectiveness in dampening gyroscopic effects and reducing engine vibration, not for aerodynamic reasons.

EXHAUST CONE

assembly consists of an outer duct, or shell, an inner cone, or tail cone, three or more radial hollow struts, and a group of tie rods. Its purpose is to channel and collect turbine discharge gases into a single jet.

TAILPIPE

an extension of the exhaust section that directs exhaust gases safely from the exhaust cone to the exhaust, or jet nozzle. It is used almost exclusively with engines that are installed within an aircraft's fuselage to protect the surrounding airframe

EXHAUST NOZZLE

provides the exhaust gases with a final boost in velocity. The two types of these designs used on aircraft are the converging design, and the converging-diverging design

Converging Exhaust Nozzle

convergent shape produces a venturi that accelerates the exhaust gases and increases engine thrust

Converging-Diverging Nozzle

the converging portion of the exhaust nozzle accelerates the turbine exhaust gases to supersonic speed at the narrowest part of the duct, then, they are accelerated further in the nozzle's divergent portion, so the exhaust gases exit the nozzle well above the speed of sound.

Mixer Unit

ensures mixing of the two streams prior to exiting the engine