Propulsion Lab 1

7/28/2019 Propulsion Lab 1

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ASSIGNME

NTSPACECRAFT PROPULSION

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TURBO SHAFT ENGINE

A turboshaft engine is similar in concept to turboprop, but instead of the propeller, the gearbox exits to

some other device. The most common use is to power a helicopter rotor. It has the following main

components.

1. Starting Generator2. Gear box3. Compressors4. Combustion5. Turbine6. Exhaust

Gear Box

There are different gears in this engine. The main function of the gear box is to control the

speed of shaft so that stalling and other phenomena does not occur which are harmful for

compressor. The gears that are used in this engine are mainly inclined spur gears.The shaft of the main gear is connected to handle which are used to rotate the shaft by hand

especially in this engine.

Starting Generator

A small generator is connected to gear box which are used only for rotation to

main shaft at the start. This generator is turn off when engine starts.

Compressors

When the flow enters the engine through the intake of the engine it moves towards the

compressor which compress the air so the pressure and density of the air rises. There are twotypes of compressor used in this engine, one is axial type and other is centrifugal. The air first

passes from the axial compressor which works in two stages. First stage is of rotor where the

dynamic pressure of air rises while static pressure rises in stator. After passing through axial

compressor the air move toward centrifugal compressor where the dynamic pressure rise occur

in impeller while total pressure rise occur in diffuser. The main advantage of using centrifugal

compressor is for reducing size of engine.

Combustion

The air directed from diffuser of centrifugal compressor moves towards the combustion

chamber where fuel are mixed and are burned by igniter at constant pressure with minimum losses. The

temperature of air rises due to which enthalpy rise occur.

Turbine

Turbine extracts energy from the air and by mean of this energy it run the compressor shaft

and also transfers high momentum air toward the exhaust. The turbine works in to three stages in which

each stage has the stator and rotor respectively.


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Exhaust

The high speed air when passes from exhaust give thrust to the engine. A pointed like object is

placed in exhaust so that it act as a nozzle.

PISTON ENGINE

This is a type of heat Engine that uses reciprocating piston to convert pressure into rotating motion.

Working

The engine that we have studied in laboratory is four stroke engine. It works in following four strokes.

1. Intake stroke2. Compression stroke3.

Power/ignition stroke

4. Exhaust strokeIntake stroke

In this stroke the piston descends from the top of the cylinder to the bottom of the

cylinder, increasing the volume of the cylinder. A mixture of fuel and air, or just air in a diesel

engine, is forced by atmospheric (or greater) pressure into the cylinder through the intake port.

The intake valve(s) then closes. The volume of air/fuel mixture that is drawn into the cylinder,

relative to the maximum volume of the cylinder, is called the volumetric efficiency of the engine.

Compression strokeIn this stroke the mixture of the air and fuel compressed by piston due to

which the temperature of the mixture rises. During this stage both the inlet and exhaust valve

are closed.

Power stroke

During this stroke the compressed mixture is ignited by spark plug due to which

the air fuel mixture is burned which increase the pressure. The resulting pressure from the

combustion of the compressed fuel-air mixture forces the piston back down toward bottom

dead Centre. This is the start of the second revolution of the cycle.

Exhaust stroke

During the exhaust stroke, the piston once again returns to top dead Centrewhile the exhaust valve is open. This action expels the spent fuel-air mixture through the

exhaust valve.


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Components of Reciprocating Engine

Almost all of the reciprocating engine are mainly consist of following parts.

Crankcase

Crankcase is the main structure of engine which contain the bearing for crankshaft. It is

designed to house crankshaft, camshaft and lubricating oil. The crankshaft must be able to endure

multidirectional forces vibration and extreme operating temperature.

Crankshaft

The crankshaft is the part of an engine that translates reciprocating linear piston motion

into rotation. To convert the reciprocating motion into rotation, the crankshaft has "crank

throws" or "crankpins", additional bearing surfaces whose axis is offset from that of the crank,

to which the "big ends" of the connecting rods from each cylinder attached.

Connecting Rods

Connecting rods connect the piston to crankshaft. It transports the force between

the piston and crankshaft.

Piston

Piston move up and down in the cylinder. It draw air/fuel mixture into cylinder and drive the

crankshaft on downward stroke. It also compress the air fuel mixture on upward stoke. Piston rings fit

into grooves on the side and form the seal between the side and cylinder wall. The ring are designed

with a gape which is forced closed when the piston is inserted into cylinder to form a spring loaded seal.

The main function of piston ring is to prevent combustion gases from escaping the cylinder

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Propulsion Lab 1