Technical Seminar.docx

VISVESVARAYA TECHNOLOGICAL UNIVERSITY, BELGAUM

VIII Sem B.E (Mechanical) Seminar Report

AIRCRAFT PROPULSION SYSTEM

By PAWAN KUMAR (1MV11ME068)

Guide: CHANDRASEKHAR B Asst. Professor Mechanical Department, Sir M.V.I.T, Bangalore

DEPARTMENT OF MECHANICAL ENGINEERING SIR M. VISVESVARAYA INSTITUTE OF TECHNOLOGY, BANGALORE Academic year: 2014 – 2015

SIR M.VISVESVARAYA INSTITUTE OF TECHNOLOGY, BANGALORE DEPARTMENT OF MECHANICAL ENGINEERING

CERTIFICATE This is to certify that Mr. PAWAN KUMAR, USN: 1MV11ME068, a student of VIII Semester B.E (Mechanical) in Department of Mechanical Engineering of Sir M. Visvesvaraya Institute Of Technology has successfully presented the seminar on the topic AIRCRAFT PROPULSION SYSTEM to fulfill the academic requirement of seminar (10ME86).

Chandrashekhar B

Dr. N Govindaraju

Faculty Supervisor

H.O.D Mechanical

Evaluators: Name

Signature with Date

1 ________________________

______________________

2 ________________________

______________________

CHAPTER 1 INTRODUCTION Aircraft propulsion system is based on Newton’s second and third law of motion. Newton’s second law states that the rate of change of momentum in any direction is proportional to the force acting in that direction. Newton’s third law states that for every action there is an equal and opposite reaction. Considering the vehicles moving entirely in fluid, the reaction principle is based on imparting momentum to a mass of fluid in such a manner that the reaction of the imparted momentum furnishes a propulsive force. The jet aircraft draws in air and expels it to the rear at a markedly increased velocity; the rocket greatly changes the velocity of the fuel which it ejects rearward in the form of product of combustion. In each case, the action of accelerating the mass of fluid in a given direction creates a reaction in the opposite direction in the form of a propulsive force. The magnitude of this propulsive force is defined as thrust. Aircraft propulsion may be achieved by using a heat engine to drive an airscrew or propeller, or by allowing a high-energy fluid to expand and leave the aircraft in rearward direction as a high-velocity jet. In propeller type of aircraft engine, the propeller takes a large mass flow and gives it a moderate velocity backwards relative to the aircraft. In jet engine, the aircraft induces a relatively small air flow and gives it a high velocity backward relative to the aircraft. In both cases the rate of change of momentum of the air provides a reactive forward thrust which propels the aircraft. The propeller type engine can be driven by a petrol engine or by a gas turbine unit. An Aircraft Engine is shown in figure 1.1.

Figure. 1.1: Aircraft Engine The different types of aircraft propulsion systems are: i. ii. iii. iv.

Propeller. Turboprop. Turbojet. Ramjet.

CHAPTER 2 HISTORY OF AIRCRAFT PROPULSION Jet engines date back to the invention of the aeolipile before the first century AD. This device directed steam power through two nozzles to cause a sphere to spin rapidly on its axis. So far as is known, it did not supply mechanical power and the potential practical applications of this invention did not receive recognition. Instead, it was seen as a curiosity. Jet propulsion only took off, literally and figuratively, with the invention of the gunpowderpowered rocket by the Chinese in the 13th century as a type of fireworks, and gradually progressed to propel formidable weaponry. However, although very powerful, at reasonable flight speeds rockets are very inefficient and so jet propulsion technology stalled for hundreds of years. The earliest attempts at airbreathing jet engines were hybrid designs in which an external power source first compressed air, which was then mixed with fuel and burned for jet thrust. In one such system, called a thermojet by Secondo Campini but more commonly, motorjet, the air was compressed by a fan driven by a conventional piston engine. Examples of this type of design were the Caproni Campini N.1, and the Japanese Tsu-11 engine intended to power Ohka kamikaze planes towards the end of World War II. None were entirely successful and the N.1 ended up being slower than the same design with a traditional engine and propeller combination. Even before the start of World War II, engineers were beginning to realize that engines driving propellers were self-limiting in terms of the maximum performance which could be attained; the limit was due to issues related to propeller efficiency, which declined as blade tips approached the speed of sound. If aircraft performance were ever to increase beyond such a barrier, a way would have to be found to use a different propulsion mechanism. This was the motivation behind the development of the gas turbine engine, commonly called a "jet" engine, which would become almost as revolutionary to aviation as the Wright brothers' first flight. The key to a practical jet engine was the gas turbine, used to extract energy from the engine itself to drive the compressor. The gas turbine was not an idea developed in the 1930s: the patent for a stationary turbine was granted to John Barber in England in 1791. The first gas turbine to successfully run self-sustaining was built in 1903 by Norwegian engineer Giddies Elling. Limitations in design and practical engineering and metallurgy prevented such engines reaching manufacture. The main problems were safety, reliability, weight and, especially, sustained operation. The first patent for using a gas turbine to power an aircraft was filed in 1921 by Frenchman Maxime Guillaume. His engine was an axial-flow turbojet. Alan Arnold Griffith published An Aerodynamic Theory of Turbine Design in 1926 leading to experimental work at the RAE.

In 1928, RAF College Cranwell cadet Frank Whittle formally submitted his ideas for a turbojet to his superiors. In October 1929 he developed his ideas further.[5] On 16 January 1930 in England, Whittle submitted his first patent (granted in 1932).[6] The patent showed a two-stage axial compressor feeding a single-sided centrifugal compressor. Practical axial compressors were made possible by ideas from A.A.Griffith in a seminal paper in 1926 ("An Aerodynamic Theory of Turbine Design"). Whittle would later concentrate on the simpler centrifugal compressor only, for a variety of practical reasons. Whittle had his first engine running in April 1937. It was liquid-fuelled, and included a selfcontained fuel pump. Whittle's team experienced near-panic when the engine would not stop, accelerating even after the fuel was switched off. It turned out that fuel had leaked into the engine and accumulated in pools, so the engine would not stop until all the leaked fuel had burned off. Whittle was unable to interest the government in his invention, and development continued at a slow pace. In 1935 Hans von Ohain started work on a similar design in Germany, initially unaware of Whittle's work. Von Ohain's first device was strictly experimental and could run only under external power, but he was able to demonstrate the basic concept. Ohain was then introduced to Ernst Heinkel, one of the larger aircraft industrialists of the day, who immediately saw the promise of the design. Heinkel had recently purchased the Hirth engine company, and Ohain and his master machinist Max Hahn were set up there as a new division of the Hirth company. They had their first HeS 1 centrifugal engine running by September 1937. Unlike Whittle's design, Ohain used hydrogen as fuel, supplied under external pressure. Their subsequent designs culminated in the gasoline-fuelled HeS 3 of 1,100 lbf (5 kN), which was fitted to Heinkel's simple and compact He 178 airframe and flown by Erich Warsitz in the early morning of August 27, 1939, from Rostock-Marienehe aerodrome, an impressively short time for development. The He 178 was the world's first jet plane. Austrian Anselm Franz of Junkers' engine division (Junkers Motoren or "Jumo") introduced the axial-flow compressor in their jet engine. Jumo was assigned the next engine number in the RLM 109-0xx numbering sequence for gas turbine aircraft powerplants, "004", and the result was the Jumo 004 engine. After many lesser technical difficulties were solved, mass production of this engine started in 1944 as a powerplant for the world's first jet-fighter aircraft, the Messerschmitt Me 262 (and later the world's first jet-bomber aircraft, the Arado Ar 234). A variety of reasons conspired to delay the engine's availability, causing the fighter to arrive too late to improve Germany's position in World War II. Nonetheless, it will be remembered as the first use of jet engines in service. Meanwhile, in Britain the Gloster E28/39 had its maiden flight on 15 May 1941 and the Gloster Meteor finally entered service with the RAF in July 1944.

Following the end of the war the German jet aircraft and jet engines were extensively studied by the victorious allies and contributed to work on early Soviet and US jet fighters. The legacy of the axial-flow engine is seen in the fact that practically all jet engines on fixed-wing aircraft have had some inspiration from this design. By the 1950s the jet engine was almost universal in combat aircraft, with the exception of cargo, liaison and other specialty types. By this point some of the British designs were already cleared for civilian use, and had appeared on early models like the de Havilland Comet and Avro Canada Jetliner. By the 1960s all large civilian aircraft were also jet powered, leaving the piston engine in low-cost niche roles such as cargo flights. The efficiency of turbojet engines was still rather worse than piston engines, but by the 1970s, with the advent of high-bypass turbofan jet engines (an innovation not foreseen by the early commentators such as Edgar Buckingham, at high speeds and high altitudes that seemed absurd to them), fuel efficiency was about the same as the best piston and propeller engines.

CHAPTER 3 AIRCRAFT PROPULSIVE DEVICE The propulsive device for aircrafts makes use of the atmospheric air as the working medium supplying oxygen for combustion of fuel. The performance of the jet engines depends on the forward speed of the engine and upon the atmospheric pressure and temperature. The propulsive devices are: i. ii. iii. iv.

Propeller. Turboprop. Turbojet. Ramjet.

3.1 Propeller Engine It is an indirect reaction device. Earlier, it was used to be driven by the reciprocating internal combustion engine. A propeller handles relatively large mass of air and accelerates it rearwards at low speed. It is the reaction of the rate of change of momentum of air, called thrust, which propels the aircraft. The function of the engine is to only revolve the propeller at the desired speed. Piston engines are, however, now only used for small aircrafts. Figure 3.1 show propeller type of aircraft engine.

Figure 3.1: Propeller Engine.

3.2 Turboprop Engine It is a combination of direct and indirect reaction devices (propeller and turbojet). Thrust is produced both by propeller and jet. Beside the compressor the turbine also drives the propeller through a reduction gear. It has thermal advantage of turbojet, combined with advantages of the propeller for efficient take off, particularly for heavily loaded aircraft.

A schematic diagram of turboprop engine is shown in fig 3.2. It comprises of a geared propeller connect to a turbojet engine. The turbine of the turboprop engine is bigger than that of the turbojet engine as it drives both the compressor and the propeller. The propeller consumes about 80 to 90 per cent of the turbine’s power and remaining 20 per cent is used for producing thrust.

Fig 3.2: Turboprop Engine In its simplest form a turboprop consists of a propeller, compressor, combustion chamber, turbine, and a gear box. Air is drawn into the intake and compressed by the compressor. Fuel is then added to the compressed air in the combustion chamber, where the combustion of fuel-air mixture takes place. The hot combustion gases expand through the turbine. Some of the power generated by the turbine is used to drive the compressor. The rest is transmitted through the reduction gearing to the propeller. Further expansion of the gases occurs in the propelling nozzle, where the gases exhaust to atmospheric pressure. The propelling nozzle provides a relatively small proportion of the thrust generated by a turboprop.

3.3 Turbojet Engine A turbojet is the most important direct reaction device. It utilizes a gas turbine power plant. In a turbine, partial expansion takes place to produce just sufficient power to drive the compressor. The exhaust of the turbine which is at pressure higher than atmospheric pressure is expanded in a nozzle given a high velocity jet. Compared to propeller units, in turbojet units a small mass of air flows through the unit, but has a high rearward velocity. Turbojets are very efficient at high speed and high altitude and inefficient at low speed and low altitude. Turbojet engine consists of Diffuser (Intake), Compressor, Combustion Chamber, Turbine, Nozzle. Turbojet engine is shown in fig 3.3

Figure 3.2: Turbojet Engine Diffuser acts as the passage for entry of the atmospheric air with a velocity equal to the velocity of the aircraft and this velocity is slowed down in diffuser. The kinetic energy of air is converted into pressure energy. Air leaving the diffuser with negligible velocity enters the compressor and is compressed to high pressure. Compressed air enters the combustion chamber where the fuel is sprayed and it is assumed that the combustion takes place at constant pressure. The product of combustion of high pressure and temperature undergo expansion to an intermediate pressure such that the output of the turbine is just sufficient to run the compressor and auxiliaries of the unit. The gases coming out of the turbine expands down to the ambient pressure and high velocity jet leaves the nozzle. This produces the required thrust and the aircraft is propelled in the forward direction. The method of propulsion is suited for the aircraft flying at the speed of 800km/h or more. A turbojet engine can’t produce the extra thrust required during take-off, for high and for increased manoeuvrings of the military aircraft. The thrust can be increased by following methods: i. ii. iii.

By increasing the mass flow rate of the working fluid: This is achieved by injecting a mixture of water and alcohol into the ram air stream of the compressor. By increasing the jet velocity: This is done by introducing an after burner in between the turbine and the nozzle. This adds up the fuel consumption. Bypass turbojet engine: The part of air drawn by fan is sent over the combustion chamber through suitable ducting, to the exhaust unit, thus bypassing the engine.

3.4 Ramjet A ramjet is a straight duct type of jet engine without a compressor and turbine wheels. The entire compression is obtained by a ram, eliminating the need of a turbine. It is the simplest device among the air breathing category. Figure 3.4 shows the ramjet engine.

Figure 3.4: Ramjet Engine It consists of a convergent-divergent diffuser, a combustion chamber and an exit nozzle. In the absence of compressor, the compression of air is obtained by the diffusion of the high velocity air steam approaching the diffuser inlet. The velocity is supersonic and the stream is first compressed adiabatically while passing through the normal and oblique shocks. The velocity after the shocks is subsonic while the diffusion takes place in the diverging section of the diffuser, the Mach number limited to about 0.25 at inlet to the combustion chamber so that the flame in the chamber is stable. The fuel is sprayed into the combustion chamber with injection nozzles and a spark plug initiates the combustion process. The product of combustion expands through the nozzle producing the required thrust.

CHAPTER 4 ADVANTAGES OF AIRCRAFT PROPULSION DEVICES 4.1 Advantages of Propeller Engines  

The propellers designed are more efficient than turbo-fans. Their cruising speed (Mach 0.7–0.85) is suitable for airliners.

4.2 Advantages of Turboprop Engines   

Efficient at low speeds. Produce greater power than a comparable piston engine with less weight, noise, and maintenance. Good take-off characteristics.

4.3 Advantages of Turbojet Engines     

No reciprocating parts. Thrust is not greatly affected by altitude. Relatively small frontal area is desirable for high speed (supersonic) use. Efficient at high speed. Efficient at high altitude.

4.4 Advantages of Ramjet Engines      

Only used in extremely high speed applications (mostly military / NASA). No moving parts. Light in weight and is less costly. No maintenance required. The system can accept large variety of fuels. The device produces greater thrust per unit weight than any other engine at supersonic speed except rockets.

CHAPTER 4 LIMITATIONS OF AIRCRAFT PROPULSION DEVICES      

The high speeds and high operating temperatures make designing and manufacturing gas turbines complex from both the engineering and materials standpoint. Complexities in manufacturing lead to a higher price. Jet engines do not produce high torque levels, which is why they aren’t used in automobiles. The noise emitted by a jet engine has many sources. These include, in the case of gas turbine engines, the fan, compressor, combustor, turbine and propeller. Difficult to start. Turbine blades need a special cooling.

CHAPTER 5 CONCLUSION  

  

Ramjet Engines are usually used for military purposes such as supersonic fighter aircrafts and in some missile for propulsion and it is also used by NASA. Ramjet Engines can’t be used in a passenger flight because of its high speed (Approximately equal to 3000km/h) and therefore other aircraft engines are used for passenger flights. Turbojet Engines are used for high speed of over 800km/h. Turboprop Engines can be used in passenger flights because of its good take-off characteristics. Propeller Engines are used in small aircraft such as trainer aircraft.

REFERENCES 1. Basic and applied Thermodynamics, Second edition, Tata McGraw Hill Education Private Limited by P.K NAG. 2. Engineering Thermodynamics, 3rd edition in S.I units by R.K.RAJPUT. 3. http://www.grc.nasa.gov/