Introduction Types of engine,airbreadthing ,non airbreadthing engine,and more Gas turbine, thermal efficiency, over all effeciency and aircraft range and endurance And many more

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Aircraft Propulsion
by
Dr. C. SURESH
Assistant Professor​
Department of Aeronautical Engineering
INSTITUTE OF AERONAUTCAL ENGINEERING

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MODULE –I: AIR-BREATHING ENGINES
 Classification, operational envelopes
 Description and function of gas generator, turbojet, turbofan, turboprop, turbo
shaft, ramjet, scramjet, turbojet/ramjet combined cycle engine
 Engine thrust, take-off thrust, installed thrust, thrust equation
 Engine performance parameters, specific thrust, specific fuel consumption and
specific impulse, thermal efficiency, propulsive efficiency, engine overall
efficiency and its impact on aircraft range and endurance
 Engine cycle analysis and performance analysis for turbojet, turbojet with
afterburner, turbofan engine, turboprop engine.

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Course Outcome
Compare the operating principles of various gas turbine engines and their
components for selecting the suitable engine as per the mission requirements.

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Contents
• Introduction

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Aircraft Propulsion

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Classification of Aircraft engines

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Which engine needs ambient air?
Why?

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Differentiate between air breathing engine and Non air
breathing engine

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Aircraft operational envelope

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Contents
1. Turboprop Engine
2. Turbojet Engine
3. Turboshaft Engine
4. Turbofan Engine
5. Ramjet Engine

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 The concept of gas-powered types of aircraft engines has improved
significantly since 1903. The gas turbine could produce enough power that
could keep an aircraft running.
 Gas-powered aircraft engines were first designed by Aegidius Elling, a
renowned Norwegian inventor. With 11 horsepower, these engines were a
massive feat back then.
 Gas-powered aircraft engines have since come a long way, and they now
come in all sizes and shape. Some engines can produce a lot more power than
the 1903 engines. Here are the common types of aircraft engines, including the
pros and cons of each engine.

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Turboprop Engine

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 The turboprop engine is a turbojet engine that uses a gearing
system to connect to the aircraft propeller.
 The gearbox of an aircraft comes with a turbojet that spins
the shaft attached to it.
 The gearbox slows down the spinning shafts to allow the gear
to connect to the propeller.
 The propeller rotates through the air to produce thrust.

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 Turboprop aircraft engines are fuel-efficient and rotate at a mid-range speed, which
can range between 250-400 knots.
 Turboprop engines are efficient at mid-range altitudes, but their gearing system can
break down quickly due to their weight.
 Their forward airspeed is also limited.
 The turboprop engine converts gas stream energy into mechanical power to derive
its propulsion.
 It produces enough power to drive the propeller load, accessories, and compressor.
 These types of engines in aircraft come with a shaft attached to the turbine that
drives the propeller through the reduction gear system

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 The first turboprop engine was designed in Budapest in
1938.
 It was tested in August 1940, but it was later abandoned
when the world war broke out.
 Max Mueller initiated the designing and launch of the
world’s first turboprop aircraft engine that started to
operate in 1942.

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Turbojet Engine
 The concept of the turbojet aircraft engine is simple.
 It entails taking air in from the engine’s rear side and then compressing it in the
compressor.
 But fuel has to be added to the combustion chamber and burned to raise the
fluid mixture temperature to about 1000 degrees.
 The hot air that is produced is then pushed through a turbine that rotates the
compressor.
 The pressure at the discharge of the turbine should be twice the pressure in the
atmosphere.
 However, that depends on the efficiency level of an aircraft engine.
 The excessive pressure then moves to the nozzle that then generates gas
streams, which are responsible for creating a thrust.

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 An afterburner can be employed to obtain a substantial increase in thrust.
 The afterburner can refer to a second combustion chamber that sits
between the nozzle and the turbine.
 Its role is to heat the gas before it gets to the nozzle.
 Increase in temperature results in about 40% increase in thrust when an
aircraft is taking off, and the push can increase at high speed once the
aircraft gets in the air.

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 These are reaction aircraft engines, which expand gases to allow the plane to
push hard forward against the atmospheric pressure.
 It sucks in air and then squeezes or compresses it to enable an aircraft to fly.
 Turbines start to spin once these gasses flow through the engine.
 The gasses then bounce back to the turbine and shoot out of the front of the
exhaust, propelling an aircraft forward.
 The turbojet works by passing air through the intake, compressor, turbine,
combustion chamber, and exhaust.

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Turboshaft Engine
 The turboshaft engine is a form of gas-powered turbine that operates the
same as a turboprop engine.
 But unlike a turboprop engine, turboshaft engines don’t drive a propeller.
Instead, it is used in helicopters to provide power to the rotor.
 Turboshaft engines are designed in a way that makes the speed of a
helicopter rotor to rotate independently of the gas generator’s speed.
 That allows the speed of a helicopter rotor to remain constant even when the
gas generator’s speed declines.
 It also modulates the power that a helicopter produces.

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 Turboshaft aircraft engines are commonly used on helicopters.
 The only difference between turbojets and turboshafts is that the latter uses
much of their power for turning a turbine instead of producing thrust.
 The turboshaft engine is similar to a turbojet engine, but it has a large shaft that
connects the front to the back.
 Since most of the turboshaft engines are used on helicopters, the shaft connects
to the transmission of the rotor blade.

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 Most parts of this engine operate the same as a turbojet engine.
 Its turbines are equipped with a shaft to power the rotor blade
transmission.
 The role of the rotor blade transmission is to transfer rotation from the
shaft to the rotor blade.
 Turboshaft engines are a little smaller than piston engines and have a
higher weight ratio compared to piston engines.
 The only downside of these engines is that their gear systems are
complex and break down easily.

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Turbofan Engine
 Turbofan jet engines are equipped with a massive fan at the front for
sucking in air.
 Turbofan jet engines are powering most of todays airliners.
 Turbofans, by contrast, separate the air flow so that only a fraction of
the air passes through the compressor blades and into the combustor
and turbines in order to drive the fan.
 The majority of the air gets compressed by the fan itself, generating the
lion’s share of thrust at low acceleration in a separate nozzle.
 The ratio between these two airflows is known as the bypass ratio,
which in the most advanced turbofan engines can be up to 12:1.

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Compare the ramjet and scramjet engines and highlight the need
for these engines in detail.

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Ramjet Engine

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 These are the lightest types of engines in aircraft and come with no moving
components. The speed of an aircraft is responsible for forcing air into the engine.
 Ramjet operates the same as a turbojet, except that the rotating parts are not
present. However, the fact that the compression ratio depends on the speed of an
aircraft restricts the application of ramjet engines.
 Unlike other engines, the ramjet does not develop static thrust; instead, it
generates little thrust below the speed of the sound. That means an aircraft
running on a ramjet engine requires assistance when taking off, which could be
in the form of another aircraft.
 The ramjet engine has been used in space vehicles and several guided-missile
systems.

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Jet engine works on
which thermodynamic
cycle ?

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Thrust Equation

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Questions
1. Total thrust is the combination of
____________&______________
2. Major part of thrust is produced due to?
3. When we will high thrust efficiency?
4. What is fuel-air ratio? Range of f?
5. What are the factors affecting thrust?
6. How thrust is produced in engine?
7. Thrust equation is derived from which principle/law?

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• What is propulsive efficiency?
• What is thermal efficiency?
• What is overall efficiency?
• What is TSFC?
• How the efficiency varies for turbo prop and
turbo jet engine?
• What is turbo shaft engine? Where it is used?

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After Burner

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After Burner

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After Burner

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Numerical Problems

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Numerical Problems

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Numerical Problems

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Numerical Problems

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Numerical Problems

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Numerical Problems

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Numerical Problems

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Numerical Problems
Air flows through a turbojet engine at the rate of 30.0 kg /s and the fuel flow
rate is 1.0 kg /s. The exhaust gases leave the jet nozzle with a relative velocity
of 610m/s. Pressure equilibrium exists over the exit plane Compute the velocity
of the airplane, if the thrust power is 1.12x106W.

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Numerical Problems
A turbojet engine is powering a fighter airplane. Its cruise altitude and Mach
number are 10 km and 0.8, respectively. The exhaust gases leave the nozzle at a
speed of 570 m/s and a pressure of 0.67 bar. The exhaust nozzle is characterized
by the ratio Ae/ṁa = 0.006 m2· s/kg. The fuel-to-air ratio is 0.02. It is required to
calculate (a) The specific thrust (T/ṁa). (b) The propulsive efficiency using the
different expressions defined above.
 At altitude 10 km, the ambient temperature and pressure are
Ta= 223.3 K and Pa= 0.265 bar
 The flight speed u = M sqrt(γ RTa)
= 239.6 m/s
 The specific thrust is
T/ṁa = 584.77 N · s/kg.

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Numerical Problems
 The propulsive efficiency is calculated by

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Numerical Problems
Air at 26 kPa, 230 K, and 220 m/s enters a turbojet engine in flight. The air mass
flow rate is 25 kg/s. The compressor pressure ratio is 11, the turbine inlet
temperature is 1400 K, and air exits the nozzle at 26 kPa. The diffuser and nozzle
processes are isentropic, the compressor and turbine have isentropic efficiencies
of 85% and 90% respectively, and there is no pressure drop through the
combustor. Kinetic energy is negligible everywhere except at the diffuser inlet and
nozzle exit. On the basis of air-standard analysis determine
(a) the pressure, in kPa, and temperatures, in K, at each principal state,
(b) the rate of heat addition to the air passing through the combustor, in kJ/s.
(c). The velocity at the nozzle exit, in m/s.

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Numerical Problems

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Numerical Problems
P01=0.77759 (from property table)
T1=254.153K

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Numerical Problems
From Property table
At P02=0.855349
h2s=505.387
P02=P01 *(P2/P1)
=0.855349

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Numerical Problems

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Numerical Problems
h4s=1187.09 KJ/Kg