Upload
ashwin-dhanapal
View
290
Download
17
Tags:
Embed Size (px)
DESCRIPTION
usefull for B.E Mechanical
Citation preview
ME2351 GAS DYNAMICS AND JET PROPULSION
Unit- IV
Jet Propulsion
Jet Propulsion
Principle of jet propulsion is obtained from the application of “Newton’s third law”
“For every action there is an equal
and opposite reaction”.
Thrust
When the fluid is to be accelerated, a force is required to produce this acceleration in this fluid.
At the same time, there is an equal and opposite reaction force acting on this fluid.
This opposite reaction force of the fluid on the engine is known as “Thrust”.
Classification of Jet Propulsion
1. Air breathing enginesCombustion takes place by using
atmospheric air.2. Rocket engines
Combustion takes place by using its own oxygen supply.
Classification of Air breathing engines
1. Ram jet engine2. Pulse jet engine3. Turbo jet engine4. Turbo prop engine5. Turbo fan engine
Ramjet Engine
Headings:1. Diagram2. Construction3. Working4. Advantages5. Disadvantages6. Applications
Diagram
Main parts
Supersonic diffuserSubsonic diffuserCombustion chamberDischarge nozzle section
Ram effect Ram Pressure:The function of supersonic and
subsonic diffusers are to convert the kinetic energy of the entering air into pressure energy. This energy transformation is called ram effect and the pressure rise is called the ram pressure.
AdvantagesVery simple and does not have any
moving parts.Low cost.Less maintenance.Better specific fuel consumption.No upper limit to the flight speed.Light weight when compared with
turbojet engine.
Dis Advantages
Take off thrust is zero, it is not possible to start a ram jet engine without an external launching device.
Very difficult to design a diffuser.Low thermal efficiency.
Applications
High speed air crafts and missiles due to its high thrust and high operational speed.
Subsonic ramjets are used in target weapons.
Pulse Jet Engine (or) Flying Bomb
Main Parts
DiffuserValve grid which contains springs that close on
their own spring pressureCombustion chamberSpark plugTail pipe or discharge nozzle.
Advantages
Very simple device next to ramjet engine.
Less maintenanceLow costLight weight when compared with
turbojet engine.
Dis AdvantagesHigh rates of fuel consumption.Maximum flight speed is limited to
750 km/h.Low propulsive efficiency than
turbojet engines.High degree of vibration leads to
noise pollution.
Applications
Subsonic flightsGerman V-I missilesTarget aircraft missilesPilotless air craft
Turbojet EngineMost common type of air breathing
engine is the turbojet engine.Main parts
1. Diffuser2. Rotary compressor3. Combustion chamber4. Turbine5. Exhaust nozzle
Diagram
Advantages
• Simple construction• Less wear and tear• Less maintenance cost• It runs smoothly• High flight speed• Low grade fuels like kerosene, paraffin can be
used. This reduces fuel cost.
Dis advantages
• Low take-off thrust and poor starting characteristics.
• High fuel consumption.• Costly materials are used.• Sudden decrease of speed is difficult.• Propulsive efficiency and thrust are lower at
lower speeds.
Applications
• Piloted air-crafts.• Military air-crafts.
Turbo-Prop Engine (or) Turbo-Propeller Engine
• It is very similar to turbojet engine. In this type, the turbine drives the compressor and propeller.
• Main parts:DiffuserCompressorCombustion chamberTurbineExhaust nozzleReduction gear and Propeller
Diagram
Advantages
• High take-off thrust• Good propeller efficiency at a speed below 800km/h.• Reduced vibration and noise.• Better fuel economy.• Easy maintenance.• Wide range of speeds.• Power output not limited.• Sudden decrease of speed is possible by thrust
reversal.
Disadvantages
• Propeller efficiency is rapidly decreases at high speeds due to shocks and flow separation.
• It requires a reduction gear which increases the cost of the engine.
• More space needed than turbo jet engine.• Engine construction is more complicated.
Applications
• The turbo prop engine is best suited for commercial and military air-craft operation due to its high flexibility of operation and good fuel economy.
Turbofan Engine
• The turbofan engine is a combination of the turbo prop and the turbojet engines combining the advantages of both.
• Main parts:– Fan– Compressor– Combustion chamber– Turbine– Fan nozzle
Diagram
By Pass Ratio:The ratio of the mass flow rates of cold air and the hot air is known as By Pass Ratio.
Advantages
• Thrust is developed is higher than turbo jet engine.
• Weight per unit thrust is lower than turbo prop engine.
• Less noise• High take-off thrust.
Disadvantages
• Increased frontal area.• Fuel consumption is high compared to turbo
prop engine.• Construction is complicated compared to
turbo jet engine.• Lower speed limit than turbojet engine.
Unit-V
Rocket Propulsion
The thrust required for the propulsion of
rocket is produced by the high velocity of
gases leaving from the nozzle which is similar
to jet propulsion.
In jet propulsion, the oxygen required for
combustion is taken from the atmosphere. But in
the case of rocket propulsion, since the altitude
of rocket engine is very high, enough oxygen is
not available in the atmosphere. So the oxygen is
filled in a tank in the rocket engine itself and
used for combustion purposes.
Classification of Rocket Engines(1)
Chemical rocket engines1. Liquid propellant rocket engine2. Solid propellant rocket engine3.Hybrid propellant rocket engine
Nuclear rocket enginesElectrical rocket enginesSolar rocket engines
Classification of Rocket Engines(2)
Based on Application1. Space rockets2. Military rockets3. Weather forecasting rockets4. Booster rockets
Based on Number of stages1. Single stage rockets2. Multistage rockets
Based on Size and Range1. Short range small rocket2.Long range large rocket
Liquid Propellant Rocket Engine
Advantages• It can be reused after recovery. So it is
economical.• Combustion process is controllable.• Speed regulation.• High specific impulse.• More economical for long range operation.• Malfunctions and accidents can be rectified at
any stage.
Disadvantages• More complicated.• High manufacturing cost.• Propellants are poisonous and corrosive.• Size and weight of the engine is more
compared to solid propellant rocket engine.• High vibration.• Proper insulation is needed.
Liquid Propellants
Types:1. Monopropellants2. Bipropellants
Monopropellants
A liquid propellant which contains both the fuel and oxidizer in a single chemical is known as monopropellant.
It is stable at normal ambient conditions and liberates thermo-chemical energy on heating.
Examples:1. Nitroglycerine2. Nitro methane3. Hydrogen Peroxide4. Hydrazine
Bipropellants
If the fuel and oxidizer are different from
each other in its chemical nature, then the
propellant is called bipropellant.
Widely used in liquid propellant rocket
systems.
Oxidizer Fuel
Liquid oxygen Gasoline, Methane, Ethanol, Hydrazine
Red fuming nitric acid Aniline, Ethanol
White fuming nitric acid
Alcohol
Hydrogen peroxide Hydrazine, Ethanol, Methanol
Properties of Liquid Propellants
• High calorific value.
• High density.
• Low vapour pressure and density.
• High specific heat and thermal conductivity.
• Products of combustion produces high jet velocity.
• Non-corrosive and non-reactive with components.
• Should not be poisonous and hazardous
• Cheap and easily available.
• Easily ignitable.
Liquid Propellant Feed System
Types:
1. Gas pressure feed system.2. Pump feed system.
Gas Pressure Feed system
Pump Feed System
Combustion
Basic Processes:InjectionAtomizationMixingVaporizationIgnitionChemical reaction between fuel and oxidizer
Various methods to atomize and mix the fuel and oxidizer
Parallel stream typeImpinging stream typeSpray injection type
Solid Propellant Rocket Engine
Advantages
• Simple in design and construction• No need for feed system (No pump & valves)• Less vibration due to absence of moving parts.• Less maintenance.• Suitable for short range applications.• Problem arising from the sudden emptying of
propellant tanks are absent.
Disadvantages• In case of emergency it is difficult to stop the
engine in the mid way.• Decrease of speed is not possible.• Low specific impulse.• Nozzle cooling is not possible.• Transportation and handling of these rockets
before firing require greater care due to the presence of propellants throughout.
Solid Propellants
Types:
1. Heterogeneous (or) Composite propellants.
2. Homogeneous propellants.
Heterogeneous propellants
Fuels:Plastics, Polymers and PVC
Oxidizers:Nitrates and Per chlorates
Homogeneous propellants
Nitroglycerine and nitrocellulose
It combines the properties of fuel and
oxidizers.
Properties of Solid Propellants
• It should release large amount of heat during combustion.
• Physical and chemical properties should not change during processing.
• High density.• It should not be poisonous and hazardous.• Cheap and easily available.• Non-corrosive and non-reactive with components of
the engine.• Storage and handling should be easy.
Hybrid propellant rocket engine
Advantages
• Speed regulation is possible by regulating the supply of oxidizer.
• High load capacity.• Hybrid rockets are lighter when compared to
the liquid propellant type rockets.• Higher fuel density.• In case of accident or crash the explosion is less
destructive compared to the liquid propellant rocket engines.
Disadvantages
• Nozzle erosion cannot be avoided.
Hybrid propellants
Fuel OxidizerBeryllium hydride FluorineLithium hydride Chlorine trifluorideLithium hydride Nitrogen tetroxide
Hydrocarbon Nitrogen tetroxide
Nuclear Rocket Engine
Electrical Rocket Engine
The fundamental requirement for rocket
propulsion is the generation of very high exhaust
velocities in order to minimize the propellant
consumption.
Electrical propulsion engines generate exhaust
velocities from about 4 to 100 times those of
chemical rocket engines.
Types of Electrical rocket engines
1. Arc plasma rocket engine
2. Ion rocket engine
3. Magneto-plasma rocket engine
Arc plasma rocket engine
Ion Rocket Engine
Magneto-Plasma Rocket Engine(or) Magneto Hydrodynamics Rocket Engine (MHD)