EG-397 Propolusion Lecture 1 test

EG-397 Propulsion:

EG-397 Propulsion Aerospace Engineering Level 3

Lecture 1 :

Lecture 1 An introduction to propulsion

Lecturer – Dr Mark Whittaker m.t.whittaker@swansea.ac.uk:

Lecturer – Dr Mark Whittaker m.t.whittaker@swansea.ac.uk Scheduled lectures: Monday 10am (Vivian Y) Wednesday (Glyndwr M) Thursday 9am (Faraday C) This will encompass 2 lectures a week, and an examples class, which will run intermittently

Course content:

Course content Assessment: 80% Examination, 20% CA (Zero tolerance on late work) Module content: [lecture hours] Propulsion unit requirements for subsonic and supersonic flight [2] Piston engine components and operation [3] Propeller theory [1] Gas turbine engines: operation, components and cycle analysis [6] Thermodynamics of high speed gas flow [2] Efficiency of components [2] Rocket motors: operation, components and design [3] Dynamics of rocket flight [2] Environmental issues [3]

Recommended texts:

Recommended texts Recommended texts: Thermodynamics, An Engineering Approach, 4th Edition, Cengel & Boyles, McGrawHill, 2002 Elements of Gas Turbine Propulsion, Mattingly, J.D., McGrawHill, 1996 Handbook of Model Rocketry, 6th Edition, Stine, Wiley 1994 Introduction to Propulsion, Archer & Salazsy, Prentice-Hall, 1996. Orbital Mechanics: Theory and Applications, Logsdon, Wiley, 1997 Further reading: The Jet Engine, Rolls-Royce plc, 1986 Jet Propulsion, 2nd Edition, Cumpsty, Cambridge, 2003

Revision of Newton’s laws of motion:

Revision of Newton’s laws of motion 1 st law Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it. 2 nd law The relationship between an object's mass m , its acceleration a , and the applied force F is F = m a . Acceleration and force are vectors (as indicated by their symbols being displayed in slant bold font); in this law the direction of the force vector is the same as the direction of the acceleration vector. 3 rd law For every action there is an equal and opposite reaction.

Classification of propulsion systems:

Classification of propulsion systems All engine types use the reaction principle to generate thrust either by Creating a jet of energy/plasma Or Powering a propeller, fan or rotor

Energy sources for propulsion:

Energy sources for propulsion The most common form of power source is chemical energy, released by combustion of fuels or propellants. However other forms of energy that can be used are Solar energy – drive a propeller in the atmosphere or as a solar sail in space Nuclear energy for a gas turbine or rocket motor Electromagnetic energy to create a plasma jet

Types of aerospace engine:

Types of aerospace engine Piston engine (Airbreather) Gas turbine (Airbreather) Ramjet (Airbreather) Rocket (Non airbreather) An airbreather is an engine that uses the air itself through which it is flying as an oxidiser for the fuel in the combustion process and as a working fluid for generating power or thrust

Airbreather type engines:

Airbreather type engines The first successful aircraft flight in 1903 was powered by a piston engine . This type of engine was dominant for the next 40 years. Piston engines were extremely successful in the first half of the century powering fighter planes that fought in both WWI and WWII.

Desirable major aerodynamic characteristics:

Desirable major aerodynamic characteristics A low drag coefficient, and a high lift/drag ratio (L/D) for cruise conditions. A high maximum lift coefficient for landing Wright brothers first aircraft had L/D ~7.5 Birds L/D 5-20 By the late 1940’s subsonic aircraft L/D~20

Supersonic flight:

Supersonic flight The 5 th Volta conference in Rome (1935) was the first serious international scientific congress devoted to the possibilities of supersonic flight. Proposal by Dr Adolf Busemann (Germany) that the swept-back wing might solve many aerodynamic problems at speeds just below and above the speed of sound. Through these investigations, the myth that sonic speed is the fundamental limit of aircraft flight velocities was overcome

The Aeropropulsion System:

The Aeropropulsion System At the turn of the 20 th century, steam and internal combustion engines were in existence but were much too heavy for flight applications The Wright brothers recognised the great future of the internal combustion engine and were able to develop both a relatively lightweight engine suitable for flight applications and an efficient propeller. The progress of propulsion systems over the years is shown in the diagram below

Slide 14:

The Wright brothers’ first aeropropulsion system had a shaft power of 12hp and its power/weight ratio was about 0.05hp/lb. NB: Power to weight ratio is the ratio of power output to total propulsion system weight, including propeller and transmission Over the next 40 years the overall efficiency and the power/weight ratio improved substantially (Power/weight by more than an order of magnitude, to about 0.8hp/lb). This improvement was brought about by a number of factors, including Engine design structures and materials Advanced fuel injection Advanced aerodynamic shapes of the propeller blades Variable pitch propellers Engine superchargers

Slide 15:

Overall efficiency (engine and propeller) reached about 28% The power output of the largest engine amounted to about 5000hp. However in the late 1930s and early 1940s the turbojet engine came into existence. The new propulsion system was immediately superior with respect to the power/weight ratio (by approximately a factor of 3) Originally its overall efficiency was much lower than that of the piston engine. Progress however was rapid. In less than 4 decades the power/weight ratio increased more than 10 fold and the overall efficiency exceeded that of a diesel propulsion system. Modern engines have power outputs in the region of 100,000hp The Rolls-Royce Trent 900

Impact on the total aircraft performance:

Impact on the total aircraft performance The previously mentioned advancements in structures and aerodynamic efficiency had a tremendous effect on flight performance, such as flight range, economy, manoeuvrability, flight speed and altitude. The increase in flight speed over the years can be seen in the figure below.

How did the jet engine come into existence?:

How did the jet engine come into existence? A number of ideas were patented in the early part of the 20 th century based on air breathing jet propulsion. Many of these clearly defined the air breathing jet principle but were not executed in practice. This was mainly due to the relationship between aerovehicle and aeropropulsion systems. In 1920 the maximum flight speed was approximately 200 miles/hour which was too slow for the jet engine to be efficient. Following this early work, much was forgotten about the possibility of the jet engine until the work done by Frank Whittle (England) and Hans van Ohain

An aside on the developers of the gas turbine engine:

An aside on the developers of the gas turbine engine Sir Frank Whittle Frank Whittle was a Royal Air Force Officer who patented the idea of a turbojet engine in 1930. The patent lapsed in 1935 because Whittle could not afford to pay the renewal fee of £5. However he was convinced by two other air force officers to revive the concept and by 1937 he had a bench test engine ready for a test run, which was successful. This developed into the promise of a contract for building a flight engine for an experimental aircraft, the Gloster E28/29, which had its first flight on May 15 th 1941. A performance demonstration to Sir Winston Churchill was particularly useful and many British companies adapted the work. Specifically Rolls-Royce developed the first production engine for the two engine Gloster Meteor, Britain’s first jet fighter (First flight 1943)

Slide 19:

Hans van Ohain Hans van ohain produced a patent on jet propulsion in 1935. His version of the engine differed from Whittle in that it used a centrifugal compressor and turbine placed very close together. Construction of the engine was completed in 1937 and the engine had its first flight in 1939, the first jet powered aircraft to fly(Heinkel He 118 dive bomber prototype) Whittle was originally angry with van Ohain when he first met him as he believed he had stolen many of his ideas. Ohain however convinced Whittle that his work had been independent and following this the two became good friends

Gas turbine engines:

Gas turbine engines Gas turbine engines were the successor to the piston engine. They became more successful as flight speeds increased towards sonic velocity. Gas turbine engines took over because of limitations in the piston engine brought about by its complexity, lack of power and excessive weight.

Operational envelopes for engines:

Operational envelopes for engines Each engine type will operate only within a certain range of altitudes and Mach numbers (velocities). Similar envelopes exist for airframes so it is important that airframe and propulsion system are matched.

Slide 22:

Approximate velocity and altitude limits for various engine types Operational envelope of an engine is bounded by a lift limit, a temperature limit and an aerodynamic force limit. The lift limit is determined by the maximum level-flight altitude at a given velocity The temperature limit will be set by the structural thermal limits of the materials used in the engine At any given altitude the maximum velocity is temperature limited by aerodynamic heating effects. At lower altitudes velocity is limited by aerodynamic force loads rather than temperature

Slide 23:

The operational limits of each propulsion system are determined by limitation of the components of the propulsion system

Air breathing engines:

Air breathing engines In this section we will have a brief overview of some of the main types of engine used to provide propulsion to aircraft, namely the turbojet, turbofan, turboprop and ramjet . It should be noted that this does not encompass all engines that provide propulsion to aircraft (e.g. reciprocating, rockets, combination types etc) nor are they used exclusively for aircraft propulsion. The thrust of the turbojet and ramjet result from the action of a fluid jet leaving the aircraft (Hence the name jet engine). Turbofan, turboprop and turboshaft engines are adaptations of the turbojet to supply thrust or power through the use of fans propellers or shafts.

Slide 25:

Gas generator The “heart” of a gas turbine type of engine is the gas generator. The compressor, combustor and turbine are the major components of the gas generator which is common to the turbojet, turbofan, turboprop and turboshaft engines. The purpose of a gas generator is to supply high-temperature and high pressure gas.

Slide 26:

The turbojet To construct a turbojet an inlet and a nozzle need to be added to a gas generator. In the analysis of a turbojet engine, the major components are treated as sections

Slide 27:

The Turbofan The turbofan engine consists of an inlet, fan, gas generator and nozzle. Part of the turbine work is used to supply power to the fan. It is generally more economical and efficient than the turbojet. The Thrust Specific Fuel Consumption (TSFC) or fuel mass flow rate per unit thrust is lower for turbofans and indicates more economical operation. The Turbofan accelerates a larger mass of air to a lower velocity for a higher propulsive efficiency. It has a larger frontal area than the turbojet, and hence more drag and weight.

Slide 28:

The Turboprop and Turboshaft A gas generator that drives a propeller is a turboprop engine. The expansion of gas through the turbine supplies the energy required to turn the propeller. The turboshaft engine is similar to the turboprop except that power is supplied to a shaft rather than a propeller. The turboshaft engine is used extensively for supplying power for helicopters, and also in VTOL (Vertical Takeoff and Landing). The Turboprop and Turboshaft have the same advantages and limitations.

Slide 29:

For low speed flight and short field takeoff the propeller has a performance advantage. At speeds approaching the speed of sound, compressibility effects set in and the propeller loses its aerodynamic efficiency. Due to the rotation of the propeller, the propeller tip will approach the speed of sound before the vehicle approaches the speed of sound. This compressibility effect when one approaches the speed of sound limits the design of helicopter rotors and propellers. At high subsonic speeds, the turbofan engine will have a better aerodynamic performance than the turboprop since the turbofan is essentially a ducted turboprop. Putting a duct or shroud around a propeller increases its aerodynamic performance Pratt & Whitney PT6 turboshaft

Slide 30:

The Ramjet The ramjet engine consists of an inlet, a combustion zone and a nozzle, but no compressor or turbine. Air enters the inlet where it is compressed and then enters the combustion zone where it is mixed with fuel and burned. The hot gases are then expelled to produce thrust. The ramjet depends on the inlet to decelerate air to raise pressure in the combustion zone. The higher the velocity of the incoming air, the higher the pressure rise. Hence the ramjet works best at supersonic velocities. At subsonic velocities the ramjet is inefficient. Also, to start the ramjet, relatively high velocity air is required to enter the inlet.

Slide 31:

The combustion process in an ordinary ramjet takes place at low subsonic velocities. At higher flight velocities a greater pressure rise occurs that can support the operation of the ramjet. The deceleration of supersonic high-velocity airstreams to subsonic velocity can result in large pressure losses and a temperature rise. This temperature increase leads to the limiting flight speed of the ramjet, because of the limitations of the wall materials and cooling methods. Research has taken place on a ramjet that can undertake the combustion process at supersonic velocities. This is a scramjet and we will talk about this later in the course

Slide 32:

The turbojet was first used as a means of aircraft propulsion by von Ohain (27/8/1939) and Whittle (15/5/1941). As development proceeded, the turbojet engine became more efficient and began to replace some of the piston engines Requirements for more thrust at relatively low speeds led to the development of the turbofan, turboprop and turboshaft engines. The thrust of a turbojet is developed by compressing air in the inlet and compressor, mixing the air with fuel and burning in the combustor, and expanding the gas stream through the turbine and the nozzle. As the gas expands through the turbine, power is supplied to the compressor. The net thrust of the engine is the result of converting internal energy into kinetic energy

Slide 33:

The diagram illustrates pressure, temperature and velocity variations through the General Electric J79 engine. In the compressor section, pressure and temperature increase as a result of work being done on the air. The temperature of the gas is further increased by burning in the combustor. In the turbine section, energy in removed from the gas stream and converted to shaft power to turn the compressor. The energy is removed by an expansion process which results in a decrease of temperature and pressure. In the nozzle, the gas stream is further expanded to produce a high exit kinetic energy. All sections of the engine must operate in such a way as to efficiently produce maximum thrust for minimum weight