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Jet Propulsion

Jet Propulsion. Lesson Objectives. After this lesson students should be able to: Define what a jet engine is Describe how Newton’s laws apply to jet or rocket engines List examples of jet engine applications List some key points in the history of jet propulsion

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Jet Propulsion

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  1. Jet Propulsion

  2. Lesson Objectives • After this lesson students should be able to: • Define what a jet engine is • Describe how Newton’s laws apply to jet or rocket engines • List examples of jet engine applications • List some key points in the history of jet propulsion • List advantages and disadvantages of jet engines

  3. Definition of a Jet Engine • An engine that burns fuel and uses the expanding exhaust gases to turn a turbine and/or produce thrust • The concept of thrust is based on the principle of Newton’s Third Law

  4. Newton’s Third Law • For every action there is an equal and opposite reaction • An example of this is a spray nozzle on a garden hose

  5. Newton’s Second LawF=M x A • Newton’s second law states - The force of an object is equal to its mass times its acceleration • The force of the spray nozzle is equal to the mass of the water multiplied by the acceleration of the water when it comes through the nozzle • This is the same principle used in rocket and jet engines

  6. Newton in Practice Schematic of a rocket engine Drawing Courtesy of Understanding Flight

  7. Where are jet engines used? Commercial Airliners – Boeing 757

  8. Where are jet engines used? Business and personal jets - Learjet

  9. Where are jet engines used? Military Bombers B-52 “Stratofortress” B-2 “Spirit” Photo Courtesy of www.af.mil

  10. Where are jet engines used? Military Fighters F-15 “EAGLE” F-22 “Raptor” Photo Courtesy of www.af.mil

  11. Where are jet engines used? Helicopters - Apache Photo Courtesy of www.army.mil

  12. Where are jet engines used? M-1 Abrams Tank Photo Courtesy of www.army.mil

  13. Where are jet engines used? Tractor Pulling Photo Courtesy of gasturbine.pwp.blueyonder.co.uk

  14. Where are jet engines used? Speed boats Photo Courtesy of gas-turbines.com

  15. History of Jet Engines • Invented in the 1930’s • Co-invented by Dr. Hans von Ohain (German) and Sir Frank Whittle (British) • Developed their ideas separately and at the time knew nothing of the other’s work

  16. History of Jet Engines • Germans were the first to utilize the jet engine as a military tool • The jet powered ME-262 was the first jet powered airplane to see combat • It had a top speed of 540 mph Photo Courtesy of Stormbirds.com

  17. History of Jet Engines • The SR-71 “Blackbird” set the current speed and altitude record for a jet powered aircraft in 1961 • Its top speed is still classified but is in excess of 2,200 mph Photo Courtesy of NASA

  18. Advantages of Jet Engines • High power to weight ratio • No reciprocating parts • Less parasitic power loss – no need to constantly accelerate and decelerate pistons • Less required maintenance

  19. Disadvantages of Jet Engines • The high speeds and high operating temperatures make designing and manufacturing gas turbines complex from both the engineering and materials standpoint • These complexities lead to a higher price • Jet engines do not produce high torque levels, which is why they aren’t used in automobiles

  20. Review Questions • Describe how a rocket or jet engine produces thrust • How do Newton’s laws relate to jet engine operation • Give some examples of jet engine applications • When and where were jet engines developed • What are some advantages of jet engines • What are some disadvantages of jet engines

  21. Types of Jet Engines

  22. Lesson Objectives • After this lesson students should be able to: • List the six different types of jet engines • Describe how each type of engine propels the vehicle it is used in • List advantages and disadvantages of each type

  23. Six different types of jet engines • Turbojet • Turbofan • Turboshaft • Turboprop • Pulsejet • Ramjet X-15 with ramjet engine Photo Courtesy of NASA

  24. Turbojet Engine • Thrust produced by gasses expelled from the exhaust nozzle • Very noisy • Used on high speed aircraft due to its small size Drawing Courtesy of Understanding Flight

  25. Turbofan • Some of the thrust is produced by gasses expelled from the exhaust nozzle just like a turbojet engine • Most of the thrust is produced from the large inlet fan • The Bypass ratio of a turbofan is typically 8:1 (eight times more air is bypassed than passes through the compressor and combustion chamber) Drawing Courtesy of Understanding Flight

  26. Turbofan Cont’ • If one wanted to increase thrust you would either have to increase the speed of the air being moved or increase the mass of the air being moved (Thrust = Mass x Acceleration) ... However… • It is more efficient to accelerate a larger mass of air to a lower velocity • Due to this principle the turbofan is more efficient than the turbojet • Due to the lower velocity the turbofan is also significantly quieter than a turbojet • Almost all modern commercial aircraft use turbofan engines (excluding the Concord)

  27. Turbofan Cont’

  28. Turboshaft • Exhaust gas is used to turn turbine shaft which is then used to propel the vehicle • Exhausted gas produces little thrust because most of the energy is used up by the turbine Drawing Courtesy of www.aircraftenginedesign.com

  29. Turboshaft Cont’ • Because of the high speed (RPM) of a turboshaft engine gear reduction must be used to obtain a usable shaft speed – much like the transmission in your car • This gear reduction also produces torque multiplication Drawing Courtesy of www.aircraftenginedesign.com

  30. Turboprop • A turboprop is essentially a turboshaft engine that is attached to a propeller • A propeller is more efficient at low speeds than a turbofan or turbojet Drawing Courtesy of www.aircraftenginedesign.com

  31. Pulsejet • Doesn’t Use a compressor or turbine • Doesn’t have the ability to produce thrust at low speed (<100 mph) • Germans used this design during WWII in their V-1 “Flying Bomb”

  32. V-1 Flying Bomb

  33. Pulsejet • Uses one-way reed valves in the front of the engine to force exhaust gasses out the rear of the engine and allow fresh air in the front

  34. Ramjet • Used for extremely high speeds (minimum 400 mph) • Doesn’t contain any moving parts (I.e.compressor, turbine, reed valves) • Relies on the inertia of the incoming air for compression • Used in the SR-71 Blackbird at supersonic speeds

  35. Review Questions • What are the six types of jet engines • What is the difference between a turbojet and a turbofan engine? • Which type of jet engine could be used to run a stationary electrical generator? • Why aren’t turbojets used in commercial aircraft anymore? Why not ramjets?

  36. Components of a Turbine Jet Engine Turbine Blade

  37. Objectives • After this lesson students should be able to: • List the basic parts required to construct a jet turbine engine • Describe the difference between an axial flow jet engine and a radial flow jet engine • List the auxiliary systems needed for various jet engines • Explain how an afterburner works

  38. Basic Components of a Turbine Jet Engine • Housing – The rigid frame that supports and contains the parts needed for operation as well as the combustion event • Air inlet and diffuser – The area of the jet where fresh air comes in, the design of the diffuser straightens and alters the speed of the incoming airs

  39. Basic Components of a Turbine Jet Engine

  40. Basic Components of a Turbine Jet Engine • Compressor – Compresses the incoming air at a ratio of approximately 30:1 • Burner or combustion chamber – The area of the engine where fuel is ignited

  41. Basic Components of a Turbine Jet Engine

  42. Basic Components of a Turbine Jet Engine • Exhaust Nozzle – accelerates the engine exhaust to the most efficient and effective speed for producing thrust • Turbine – Converts the energy from the heated and expanding exhaust gasses to a rotating shaft which is used to turn the compressors, or in the case of a turboshaft engine, power the vehicle

  43. Basic Components of a Turbine Jet Engine

  44. Radial vs. Axial Flow • Axial flow compressors – the air travels along the axis of the engine • Radial flow engines use a centrifugal compressor – they push the air out radially rather than along the axis of the engine

  45. Radial vs. Axial Flow • Axial flow compressors are more efficient • Radial flow compressors are less expensive • Most large and high-performance jet engines use an axial flow configuration

  46. Other Essential Systems • Fuel System • Ignition System • Flame Holder • Lubrication System

  47. Other Auxiliary Components • Turbofan – Inlet fan • Turboshaft – Gear reduction unit • Turboprop - Gear reduction unit • Pulsejet – reed valves • Afterburners • Thrust Vectoring Systems

  48. Turbofan Inlet Fan • Most of the thrust is produced from the large inlet fan • The Bypass ratio of a turbofan is typically 8:1

  49. Turboshaft Gear Reduction Unit

  50. Pulsejet Reed Valves The reed valves force the expanding exhaust gasses out the rear of the engine and allow fresh air to enter the front

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