`

Project Report
On
Aircraft Propulsion Systems

By:
Kanishka Shukla (XI)
Param Singh Bhatia (IX)
Mihir Soni (IX)

School: Bhavan’s R K Sarda Vidya Mandir, Raipur,

Chhattisgarh

Mentor- Rajat Ahuja

 INDEX
Page
Introduction…………………………………………………………….….....1
Characteristics……………………………………………………………......1
Classification of Aircraft Propulsion System………………………….…......2
1. External combustion engines
1.1. Steam engine…………………………………………......3
1.2. Stirling engine…………………………………………....3
1.3. Nuclear engine…………………………………………...4
2. Internal combustion engines
2.1 Shaft Engine
2.1.1 Intermittent Combustion
2.1.1.1 Wankel Engine………………………....4
2.1.1.2 Reciprocating Engine
2.1.1.2.1 Inline………………………...5
2.1.1.2.2 Rotary…………………….....5
2.1.1.2.3 Radial…………………….....6
2.1.1.2.4 V-Type…………………..….6
2.1.1.2.5 Opposed………………….....7
2.1.2 Continuous Combustion Engine
2.1.2.1 Turbo prop engine……………………..7
2.1.2.2 Turbo shaft engine………………….....8
2.1.2.3 Prop fan engine………………………..9
2.2 Reaction Engine
2.2.1 Turbine based
2.2.1.1 Turbojet……………………………....10
2.2.1.2 Turbofan……………………………...10
2.2.1.3 Turbo-ram jet………………………....11
2.2.1.4 Turbo-rocket………………………….12
2.2.1.5 Advanced ducted……………………..12
2.2.2 Athodyd (Aero THermODYnamic Duct)
2.2.2.1 Ram jet…………………………….....13
2.2.2.2 Pulse jet………………………………14
2.2.2.3 Scram jet………………………….….15
3. Other Engines
3.1. Electric powered aircraft……………………….….16
3.2. Human powered aircraft……………………….…..17
Comparative Analysis……………………………………………………..18
Conclusion………………………………………………………………...22
References…...............................................................................................22
 Page 1

INTRODUCTION
An aircraft engine, also known as an aero engine, serves as the propulsion system for an
aircraft, acting as a crucial component or the core element in the advancement of aviation.
The progress of aero engines and aircraft structures has been intertwined since the
inception of successful flight. As the global demand for air travel increases there is a
growing need for more efficient, sustainable, and quieter propulsion options. The
engineering behind modern aircraft engines shows a complex interrelation of
aerodynamics, thermodynamics, and materials science, resulting in systems that not only
deliver exceptional performance but also prioritize environmental sustainability.
Recent advancements in propulsion technology are particularly significant. The integration
of high-bypass turbofan engines, for example, has significantly enhanced fuel efficiency
while reducing noise levels, making air travel more accessible and environmentally
friendly. Moreover, the development of hybrid-electric and fully electric propulsion
systems represents a pivotal shift towards greener aviation, aiming to minimize carbon
emissions and reliance on fossil fuels.
Furthermore, innovations in materials—such as advanced composites and lightweight
alloys—are crucial in enhancing the overall efficiency and performance of engines. These
materials contribute to reduced weight, improved thermal resistance, and longer service
life, all of which are essential for modern aircraft design.
In brief, the aircraft propulsion system is at a transformative stage, propelled by
innovations that not only enhance performance and efficiency but also address significant
environmental concerns.

CHARACTERISTICS
Aero engines are required to possess the following characteristics:
1. Reliability: Given that power loss in an aircraft poses a significantly greater challenge
than in road vehicles, aero engines must be exceptionally reliable.

2. Operational Resilience: Aero engines must be capable of functioning under extreme

conditions of temperature, pressure, and speed.

3. Lightweight Design: It is imperative for aero engines to be lightweight to avoid

increasing the empty weight of the aircraft, consequently preserving payload capacity.

4. Powerful Performance: The engines must exhibit substantial power to effectively

overcome the combined influences of aircraft weight and drag.

5. Compact and Streamlined: To minimize drag, aero engines should be designed to be

small and easily streamlined.

6. Field Reparability: Ensuring cost-effectiveness, aero engines should be field-

repairable, enabling minor repairs to be undertaken inexpensively and outside of
specialized facilities.
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7. Fuel Efficiency: A crucial factor for achieving the desired range and manoeuvrability,
aero engines should demonstrate high fuel efficiency aligned with the aircraft's design
requirements.

8. High-Altitude Operation: Capability to operate efficiently at sufficient altitudes is

essential for the diverse operational needs of the aircraft.

9. Low Noise Generation: Striving for minimal noise generation, aero engines should be
designed to produce the least amount of noise during operation.

10. Low Emissions: In alignment with environmental concerns, aero engines should
generate the least emissions, contributing to a more sustainable and eco-friendly
aviation landscape.

CLASSIFICATION OF AIRCRAFT PROPULSION SYSTEM

AIRCRAFT
ENGINES

External Internal
combustion combustion Other engines
engines engines

Electric powered
Steam engine Shaft Engine Reaction Engine
aircraft

Intermittent Continuous
Human powered
Stirling engine Combustion Combustion Turbine based Athodyd
aircraft
Engine Engine

Reciprocating Turboprop
Nuclear engine Wankel Engine Turbo-ram jet Ram jet
Engine engine

Turbo shaft
Inline Turbo-rocket Pulse jet
engine

Rotary Prop fan engine Turbo-jet Scram jet

Opposed Turbo-fan

V-type

Radial

Fig.1 Classification of Aircraft propulsion system

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1. External Combustion engine-

External combustion engines comprise of steam, Stirling, or nuclear engines, where
all the heat transfer occurs through the engine wall. This is in contrast to internal
combustion engines, which generate heat by burning fuel in a combustion chamber
that is an integral part of the working fluid flow circuit.
1.1. Steam Engine-
Steam-powered aircraft are vehicles
that use steam engines for propulsion.
These aircraft operate by boiling
water to produce steam, which then
drives pistons or turbines to generate
thrust. While steam power was an
early method of aviation, it was
eventually replaced by more efficient
internal combustion engines and jet
propulsion systems.
Fig.2 Aerial Steam Carriage
Advantages- Source-Wikipedia
 The benefits of this engine included the elimination of audible noise and
disruptive vibrations, increased efficiency at both low engine speeds and higher
altitudes, aided by lower air temperatures facilitating condensation.
 Additionally, there was a diminished risk of engine failure, leading to reduced
maintenance and fuel costs.

Limitations-
 Steam engines are only appropriate for small aircrafts while large ones need
heavy boilers, piping and other accessories.
 Scaling up steam reciprocating engines to meet the requirements of larger aircraft
proved impractical.
1.2. Stirling Engine-
A Stirling engine is a heat engine
having either air or other gas as a
working fluid. It operates by cyclic
compression and expansion of the
working fluid, at different
temperature levels such that there is a
net conversion of heat energy to
mechanical work.
Fig.3 Stirling Engine
Advantages-
Source- American Stirling Company
 High power density and low cost,
 Quieter, less polluting and gain efficiency with altitude due to lower ambient
temperatures;
 Page 4

 More reliable due to fewer parts and the absence of an ignition system, produce
much less vibration (airframes last longer), and safer, less explosive fuels may be
used.
Limitations-
 Low power density- Stirling engines generally produce less power for their size
compared to other engine types, making them less suitable for high-power
applications.
 Stirling engines typically have a slower response time compared to internal
combustion engines, which can affect performance in dynamic applications.
1.3. Nuclear Engine-
A nuclear-powered aircraft refers to an aircraft propelled by nuclear energy.
During the Cold War, the United States and the Soviet Union both researched these
aircraft, motivated by the idea that they could allow a nation to keep nuclear bombers
in continuous flights for prolonged periods, thereby enhancing its nuclear deterrence
strategy. However, neither country successfully produced nuclear aircraft in
significant quantities.
Advantages-
 Nuclear engines could enable aircraft to fly much longer distances without the
need for frequent refueling, enhancing operational capabilities.
Limitations-
 One ongoing design challenge that was never completely addressed was the need
for significant shielding to protect the crew from radiation sickness.
 The potential radiation fallout if one of these aircraft were to crash in a populated
area was considered to have devastating consequences.

2. Internal combustion engines-

Aircraft internal combustion engines (ICEs) have been a fundamental part of aviation
history. An internal combustion engine is a heat engine where fuel combustion takes
place within a combustion chamber that is a key component of the working fluid flow
circuit. Internal combustion engines can be broadly categorized into two groups: shaft
engines and reaction engines.
2.1. Shaft Engine-
2.1.1. Intermittent combustion
2.1.1.1. Wankel Engine-
Invented by German
engineer Felix Wankel in
1950, the Wankel engine
is a form of internal
combustion engine
employing a rotary design
to convert pressure into
rotational motion.
Fig.4 Wankel engine
Source-Wikipedia
 Page 5

Advantages-
 The Wankel engine is generally more compact and lightweight than equivalent
piston engines, allowing for more efficient use of space in vehicles.
 These engines have high power-to-weight ratio, making them popular in
performance vehicles.
Limitations-
 Wankel engines tend to be less fuel-efficient than conventional piston engines,
particularly at lower RPMs.
 They can produce higher emissions due to incomplete combustion, which can be a
concern in meeting regulatory standards.
2.1.1.2. Reciprocating Engine
A reciprocating engine, commonly referred to as a piston engine, is a heat
engine that utilizes one or more reciprocating pistons to convert pressure into
rotational motion. Piston engines can be categorized into five groups i.e. in-
line, rotary, V-type, radial, and opposed. These engines are paired with a
propeller to propel the forward motion of airplanes.
2.1.1.2.1.Inline engine-
An in-line engine arranges its
cylinders in a single row,
typically featuring an even
number of cylinders, although
instances of three- and five-
cylinder engines exist.

Advantages- Fig.5 Inline engine (Source- alamy)

 The primary advantage of an in-line engine lies in its ability to facilitate
the design of an aircraft with a narrow frontal area, minimizing drag.
 Balanced firing order, which helps minimize vibrations and noise.
 Inline engines typically have better airflow around the cylinders,
facilitating effective cooling and improving overall thermal efficiency.
Limitations-
 Suboptimal power-to-weight ratio due to the elongated and consequently
heavy crankcase and crankshaft.
2.1.1.2.2. Rotary engine-
In a rotary engine, all cylinders are
arranged in a circular configuration
around the crankcase, resembling a
radial engine. The key distinction
lies in the fact that the crankshaft is
attached to the airframe, while the
propeller is affixed to the engine
case.
Fig.6 Rotary engine
Source-Wikipedia
 Page 6

Advantages-
 Rotary engines are generally smaller and lighter than conventional piston
engines, enhancing aircraft performance and efficiency.
 Rotary engines typically have a rapid response to throttle changes,
improving performance during takeoff and maneuvers.
Limitations-
 Rotary engines often have lower fuel efficiency than traditional piston
engines, especially at lower RPMs.
 They can produce more emissions due to incomplete combustion, making
regulatory compliance challenging.
2.1.1.2.3. Radial engine-
Radial aircraft engines are a
type of internal combustion
engine that features a
distinctive design, with
cylinders arranged in a
circular pattern around a
central crankshaft.
Advantages- Fig.7 Radial engine (Source-Wikipedia)
 Radial engines can deliver significant power, making them suitable for
larger aircraft and high-performance applications.
 .The arrangement of cylinders exposes a significant portion of the engine's
heat radiating surfaces to the air, resulting in even cooling and smooth
operation by canceling reciprocating forces.
Limitations-
 Radial engines can be heavier than other engine types, which may affect
overall aircraft weight and performance.
 .While powerful, radial engines are often less fuel-efficient than modern
turbine engines, especially at higher speeds and altitudes.
2.1.1.2.4. V-Type engine-
In a V-type engine, cylinders
are organized into two in-line
banks, positioned at an angle
of 30-60 degrees apart from
each other. The predominant
configuration for V engines
involves water cooling.
Advantages- Fig.8 Wright Hispano-Suiza H, V-8 Engine
 V-type engines often provide strong torque at low RPMs, which is
beneficial for takeoff and climb performance.
 These engines can be found in a range of applications, from general
aviation to military aircraft.
 Page 7

Limitations-
 The V configuration can affect the center of gravity and weight
distribution, potentially impacting aircraft handling.
 While powerful, V-type engines can be less fuel-efficient than modern
turbine engines, particularly at higher speeds.
2.1.1.2.5. Opposed engine-
An opposed-type engine
features two sets of cylinders
positioned on opposite sides
of a centrally located
crankcase In aircraft, opposed
engines are typically installed
with the crankshaft positioned
horizontally, while in Fig.9 Kemp G-2 Horizontally-opposed Engine
helicopters, they may have a Source-Smithsonian
vertical crankshaft orientation.
Advantages-
 The crankshaft is located centrally and is designed to balance the opposing
forces created by the cylinders, which helps reduce vibrations.
 The flat design contributes to a lower center of gravity in the aircraft,
enhancing stability and handling.
Limitations-
 While suitable for smaller aircraft, opposed engines may struggle to
deliver the high power outputs needed for larger or faster aircraft.
 In some designs, ensuring even cooling across all cylinders can be a
challenge, particularly in high-performance applications.

2.1.2. Continuous combustion

Continuous combustion engines predominantly consist of turbine shaft engines,
incorporating turbo-prop, turbo-shaft, and prop-fan engines.
2.1.2.1. Turbo-prop engine
These engines consist of a gas generator, encompassing a compressor,
combustion chamber, and turbine, along with a propeller. The turbine
serves the dual purpose of driving both the compressor and the propeller.
Due to the optimal spinning speed of gas turbines being high, a turboprop
incorporates a gearbox to reduce the shaft speed, preventing the propeller
tips from reaching supersonic speeds.

Fig.10 Turbo-prop engine

Source- Britannica
 Page 8

An alternative design involves the addition of a second turbine to the

turboprop engine, which exclusively drives the propeller either directly or
through a gearbox. In this configuration, the first turbine is dedicated to
driving the compressor, allowing it to rotate freely at its optimal speed,
referred to as a free- or power-turbine, while the other turbine is
designated as the compressor-turbine. Modern turboprop engines generate
thrust from both the propeller and the exhaust jet stream, with
approximately 10-20% of the thrust produced by the jet stream.

Advantages-
 Turboprop engines are more fuel-efficient than turbojet engines at lower
speeds and altitudes, making them ideal for regional and short-haul flights.
 They offer excellent climb rates, making them effective for operations in
mountainous or challenging terrains.
Limitations-
 Turboprops are generally less efficient at higher speeds, which can limit
their use for long-distance flights compared to jet engines.
 The propeller can produce more noise and vibrations than jet engines,
which may be a concern in some operational environments.
2.1.2.2. Turbo-shaft engine
Turbo-shaft engines are primarily utilized in helicopters and auxiliary
power units. The design of a turbo-shaft engine closely resembles that of
a turboprop, with a notable distinction: in a turboprop, the engine
supports the propeller, and the entire assembly is attached to the airframe.
Conversely, in a turbo-shaft configuration, the engine does not directly
provide physical support to the helicopter's rotors. Instead, the rotor is
linked to a transmission, which is bolted to the airframe, and the turbo-
shaft engine supplies power to the transmission through a rotating shaft.

Fig.11 Turbo-shaft engine

Advantages- Source- Research Gate
 Turbo-shaft engines are highly efficient at converting fuel into power,
making them ideal for helicopter operations and other applications
requiring sustained power output.
 Beyond helicopters, turbo-shaft engines can also power other applications
such as auxiliary power units (APUs) and some fixed-wing aircraft.
 Page 9

Limitations-
 Turbo-shaft engines can be quite noisy, particularly in helicopter
applications, which can be a concern in urban areas.
 While efficient for power delivery, turbo-shaft engines are not designed for
high-speed flight, making them less suitable for fixed-wing aircraft focused
on speed.
2.1.2.3. Prop fan engine-
A prop-fan, often referred to as an un-ducted fan, is a modified turbofan
engine design in which the fan is mounted externally to the engine casing,
aligned with the same axis as the compressor blades.

Fig.12 Prop-fan engine (Source- GE Aerospace)

Prop-fans are alternatively referred to as ultra-high bypass (UHB) engines
and, more recently, open rotor jet engines. This design aims to combine
the speed and performance attributes of a turbofan with the fuel efficiency
of a turboprop.
The prop-fan concept emerged as an effort to achieve superior fuel
efficiency compared to contemporary turbofans, though this comes with
the exchange of higher noise levels. Most prop-fans are still in the
experimental phase.

Advantages-
 The design aims to achieve high aerodynamic efficiency, particularly at
subsonic speeds and operate more quietly than conventional propeller
engines.
 Prop-fans can provide a significant amount of thrust relative to their
weight, making them suitable for a range of aircraft applications.
Limitations-
 Their efficiency may decrease at higher speeds, making them less suitable
for certain long-distance jet applications.
 The design and engineering of prop-fans can be more complex than
traditional engines, leading to potential maintenance challenges.
2.2. Reaction Engine-
Reaction-type aircraft engines, commonly referred to as jet engines, operate on the
principle of Newton's third law of motion: for every action, there is an equal and
opposite reaction. These engines generate thrust by expelling a high-speed jet of
exhaust gases, creating a forward force.
 Page 10

2.2.1. Turbine based

2.2.1.1. Turbojet
They were among the first types of jet engines developed and are known
for their simplicity and effectiveness. A turbojet consists of several key
components: an air intake, a compressor, a combustion chamber, a
turbine, and a nozzle. All the turbines employed are of the axial type.
Axial compressors and turbines consist of multiple blade rows: some
rotating, known as the rotor, and others stationary, identified as the stator.

Fig.13 Turbo-jet engine (Source-ResearchGate)

To enable fighter planes to achieve supersonic speeds, an afterburner is
incorporated into a core turbojet. Activating the afterburner involves
injecting extra fuel, which burns to generate additional thrust. When the
afterburner is deactivated, the engine functions similarly to a basic
turbojet.

Advantages-
 Turbojet engines can produce a significant amount of thrust, making them
suitable for fast aircraft.
 The design is relatively straightforward compared to other jet engines,
allowing for easier maintenance.
Limitations-
 Turbojets are less fuel-efficient at subsonic speeds compared to turbofan
engines, making them less suitable for commercial aviation.
 They tend to produce more noise than turbofan engines, which can be a
concern in urban areas and near airports.
2.2.1.2. Turbofan
Turbofan aircraft engines are a type of jet engine widely used in
commercial and military aviation. They combine the features of a turbojet
with a large fan at the front, which provides additional thrust and
improves efficiency.
The incoming air is captured by the engine inlet. Part of this air passes
through the fan and proceeds into the core compressor and then the
burner, where it mixes with fuel for combustion. The resulting hot
exhaust moves through the core and fan turbines before exiting through
the nozzle, similar to a basic turbojet. The remaining incoming air
bypasses the core, flowing around the engine, much like air through a
 Page 11

propeller. The air passing through the fan gains a slightly increased
velocity from free stream.

Fig.14 Turbo-fan engine (Source- ResearchGate)

Consequently, a turbofan derives thrust from both the core and the fan.
The ratio of air bypassing the core to the air passing through it is termed
the bypass ratio.
Engines with bypass ratios of 1-2 are generally categorized as low bypass
ratio turbofans, while high bypass turbofans, prevalent in current
transport aircraft, have bypass ratios continuously increasing, reaching 10
or more in some cases.

Advantages-
 Turbofan engines are more fuel-efficient than turbojets, especially at
subsonic speeds, making them ideal for commercial airliners.
 The large fan and bypass air help to lower noise levels, making turbofans
quieter than turbojets, which is beneficial for airport operation
Limitations-
 While effective for subsonic flight, turbofans may not be as efficient as
turbojets at supersonic speeds, which limit their use in supersonic aircraft.
 The design of turbofan engines is more complex than that of turbojets,
which can lead to higher maintenance costs.
2.2.1.3. Turbo-ram jet
The turbo ramjet is a hybrid engine designed to function as both a turbojet
and a ramjet, catering to high-speed flight. This jet engine, illustrated in
this Figure, seamlessly integrates the turbojet's capabilities for speeds up
to Mach 3 with the ramjet's superior performance at higher Mach
numbers.

Fig.15 Turbo-ram jet engine

Source- Softecks
 Page 12

Advantages-
 By combining turbojet and ramjet technologies, this engine can achieve
better fuel efficiency and thrust performance compared to traditional
designs.
 Turbo-ramjets can be effective at high altitudes where traditional turbojet
engines may struggle due to thin air.
Limitations-
 The dual-mode design introduces complexity in terms of engine control and
operation, requiring advanced systems to manage the transition between
modes.
 The high temperatures experienced in ramjet mode can present challenges
in terms of materials and cooling systems.
2.2.1.4. Turbo-rocket
A turbo-rocket engine combines elements of both turbojet and rocket
engine technologies to provide thrust for aircraft, particularly in high-
speed and high-altitude environments. This hybrid design is designed to
optimize performance by utilizing air-breathing capabilities at lower
speeds and transitioning to rocket propulsion at higher speeds.

Fig.16 Turbo-rocket engine (Source- ResearchGate)

Advantages-
 By using atmospheric oxygen in turbojet mode, the engine can achieve
better fuel efficiency compared to traditional rocket engines that carry all
their oxidizers.
 The ability to switch to rocket mode allows for high thrust levels when
needed, particularly during takeoff and acceleration phases.
Limitations-
 Operating at high speeds generates significant heat, necessitating robust
cooling solutions to prevent engine damage.
 The Despite being smaller and lighter than the turbo ramjet, the turbo-
rocket exhibits higher fuel consumption.
2.2.1.5. Advanced ducted-
Advanced ducted fans essentially resemble turbofans, featuring large
swept fan blades equipped with pitch control and reduction gearing
similar to prop-fans. However, these fans are enclosed in ducts akin to
turbofan engines. The bypass ratio for advanced ducted fans typically
ranges from 15:1 to 25:1.
 Page 13

Fig.17 Advanced ducted engine

Advantages- Source- inphoenixaviation
 The high bypass ratio and ducted design contribute to lower fuel
consumption, making these engines particularly suitable for commercial
aviation.
 The ducted configuration significantly reduces noise, making aircraft
equipped with these engines more suitable for urban environments and
compliant with noise regulations.
Limitations-
 While efficient at subsonic speeds, ducted fans may face challenges in
terms of performance at higher speeds compared to conventional turbojets
or turbofans.
 Research and development for advanced ducted engines can be costly, and
widespread adoption may be limited by these financial considerations.

2.2.2. Athodyd (Aero THermODYnamic Duct)

2.2.2.1. Ram jet
A ramjet, sometimes colloquially known as a stovepipe jet, represents a
type of jet engine that utilizes the forward motion of the engine to admit
and compress incoming air, dispensing with the need for a rotary
compressor.

Fig.18 Ram jet engine (Source- ScienceDirect)

Ramjets are incapable of generating thrust at zero airspeed, making it
impossible to propel an aircraft from a standstill. The ramjet comprises
three essential modules: an inlet duct, a burner or combustor, and a nozzle.
There are two types of ramjets: liquid-fuel and solid-fuel ramjets. Ramjet
engines can operate at either subsonic or supersonic speeds. Subsonic
ramjets do not require a sophisticated inlet, as the airflow is already
subsonic, typically utilizing a simple hole.
 Page 14

In contrast, supersonic ramjets decelerate supersonic flow to subsonic

speeds at the inlet through one or more oblique shock waves, terminated by
a strong normal shock.
Consequently, air achieves subsonic velocities upon entering the
combustion chamber. The combustor enhances the compressed air by
introducing heat and mass through the combustion of fuel. Within the
combustion chamber, flame holders prevent the flames from extinguishing.

Advantages-
 Ramjets are highly efficient at supersonic speeds, making them ideal for
high-speed flight applications.
 Ramjets can produce significant thrust relative to their size and weight,
especially at higher speeds.
Limitations-
 Ramjets are not effective at subsonic speeds and typically require a separate
propulsion system (like a turbojet) for takeoff and initial acceleration.
 They cannot generate thrust at low speeds, making them unsuitable for all
phases of flight without assistance from another engine type.
2.2.2.2. Pulse jet
A pulse jet engine, often referred to as a pulsejet, is a straightforward form
of jet engine characterized by intermittent combustion pulses. Unlike
ramjets, which employ a continuous combustion process, pulsejets utilize
intermittent combustion. These engines are distinctive due to their ability to
operate statically with minimal or no moving parts.
There are two primary types of pulsejet engines: valved and valve less.
Both types utilize resonant combustion and harness the expanding
combustion products to generate a pulsating exhaust jet, producing
intermittent thrust.
In valved engines, a mechanical one-way valve, typically straightforward
leaf-spring type of shutter, is employed. When the valve is open, a new air
charge is allowed to enter. This air mixes with the fuel, leading to an
explosion that subsequently closes the valve. This closure forces the hot gas
to exit solely through the tailpipe at the rear of the engine, creating space
for fresh air and additional fuel to enter through the intake. The superheated
exhaust gases then exit through an acoustically resonant exhaust pipe

Fig.19 (a) Valved Pulse jet engine

Source- ScienceDirect
 Page 15

Valve less pulsejets, devoid of any moving parts, rely solely on their
geometric configuration to regulate the exhaust flow from the engine.
These engines expel exhaust through both the intakes and the exhaust, with
the objective of directing the majority of the exhaust through the longer
tailpipe for enhanced propulsion efficiency.

Fig.19 (b) Valve-less Pulse jet engine (Source- ScienceDirect)

Advantages-
 Pulsejets can produce significant thrust relative to their weight, especially
at high speeds.
 The absence of complex mechanical components makes pulsejet engines
lighter than traditional jet engines.
Limitations-
 Pulsejet engines are notoriously loud, producing a distinctive and often
disruptive sound due to the rapid combustion cycles.
 The pulsing nature of combustion can lead to vibrations and stability issues,
affecting the overall performance of the aircraft.
2.2.2.3. Scram jet
A scramjet (supersonic combustion ramjet) engine is an advanced type of
air-breathing jet engine designed to operate efficiently at hypersonic
speeds, typically above Mach 5. Unlike traditional jet engines that use a
mechanical compressor, scramjets rely on the high speed of the aircraft to
compress incoming air for combustion.
The propulsion system comprises five major engine components (internal
inlet, isolator, combustor, internal nozzle, and fuel supply subsystem) and
two vehicle components (the craft's forebody, crucial for air induction, and
aft-body, a critical part of the nozzle component).
Advanced cooling methods are employed to manage the extreme
temperatures generated during operation, often using specialized materials
and thermal protection systems.

Fig.20 Scram jet engine (Source- ResearchGate)

 Page 16

Advantages-
 Scramjets are capable of achieving and sustaining hypersonic speeds with
greater efficiency than traditional rocket engines, as they use atmospheric
oxygen for combustion.
 By using air-breathing technology at high speeds, scramjets have the
potential for longer ranges compared to rocket-only systems
Limitations-
 Scramjets require a significant initial speed (usually above Mach 5) to
operate effectively, which means they often need to be launched from a
high-speed platform or another propulsion system.
 The extreme temperatures experienced during hypersonic flight present
significant engineering challenges, particularly regarding materials and
cooling systems.
3. Other engines-
3.1. Electric powered aircraft-
Electric-powered aircraft utilize electric propulsion systems, typically powered by
batteries or fuel cells, to achieve flight. These aircraft are powered by electric motors,
which convert electrical energy into mechanical energy to drive propellers or fans.

Advantages-
 This technology is gaining traction in the aviation industry due to its
potential for reducing emissions, noise, and operating costs.
Limitations-
 Current battery technology limits the range and endurance of electric
aircraft compared to conventional aircraft, making them more suitable for
short-haul flights.
 Electric aircraft may have restrictions on payload capacity, particularly for
larger commercial applications, due to weight constraints of current battery
systems.
Net system efficiency of an ICE propulsion system versus an Electric propulsion
system-
The values are summarized in the table below, highlighting the high efficiency of
electric propulsion systems alongside their relatively low overall net system
efficiency in brake power per unit weight. This lower efficiency is primarily due to
the significant weight of the batteries, which negatively impacts the net weight
efficiency of electric propulsion systems.
 Page 17

Fig.21 Conventional V/s electric powered engine

Source- Embry-Riddle Aeronautical University
3.2. Human powered aircraft
A human-powered aircraft (HPA) is
an aircraft that achieves sustained and
controlled flight solely through human
power, typically generated by
pedaling, which activates a
mechanism turning a propeller for
propulsion.

Fig.22 Human powered aircraft

Advantages- Source- Wikipedia
 HPAs rely entirely on human power; they produce zero emissions, making them
environmentally friendly.
Limitations-
 Human power is significantly less than mechanical power, limiting the speed and
endurance of the aircraft.
 To maximize efficiency, HPAs must be very light, which can restrict the materials
and technology used in construction.
 Page 18

COMPARATIVE ANALYSIS

On the basis of fore mentioned characteristics, comparative analysis of the engines is given as
under-

1) Comprehensive comparison of Inline, Rotary, Radial, V-Type, and Opposed aircraft

engines-

Rotary Radial V-Type Opposed

Parameter Inline Engine
Engine Engine Engine Engine
Otto or Diesel Otto or Diesel Otto or Diesel Otto or Diesel
Process Wankel Cycle
Cycle Cycle Cycle Cycle
Compact, V-shaped Flat,
Linear, Circular
Design rotating (typically 60° horizontally
compact arrangement
assembly or 90°) opposed
Gasoline, Gasoline, Gasoline, Gasoline, Gasoline,
Fuels Used
Avgas, Diesel Avgas Avgas, Diesel Avgas, Diesel Avgas, Diesel
Moderate to Moderate to Moderate to
Initial Cost Moderate Moderate
High High High
Moderate to Moderate to
Overall Moderate (20- Moderate (30- Moderate (30-
High (30- High (30-
Efficiency 30%) 40%) 40%)
40%) 50%)
0.35 - 0.45 0.5 - 0.7 0.4 - 0.6 0.35 - 0.55 0.35 - 0.5
Fuel Efficiency
lb/hp/hr lb/hp/hr lb/hp/hr lb/hp/hr lb/hp/hr
Power
Smooth Pulsating Smooth Smooth Smooth
Delivery
High (85- Moderate (70- High (80- High (85- High (85-
Reliability
95%) 80%) 90%) 95%) 95%)
Very Good
Performance Limited (up to
Good Good (up to 400 Good
at High Speeds 200 knots)
knots)
Thrust-to-
0.4 - 0.6 0.8 - 1.2 0.6 - 1.0 0.5 - 0.8 0.5 - 0.7
Weight Ratio
Speed Up to 300 Up to 200 Up to 300 Up to 400 Up to 250
Capabilities knots knots knots knots knots
Moderate (75- High (90-100 Moderate (80- Moderate (75- Moderate (75-
Noise Levels
85 dB) dB) 90 dB) 85 dB) 85 dB)
Vibrations Low High Moderate Low Low
Cooling
Good Moderate Good Good Good
Efficiency
600 - 1,200 400 - 800 600 - 1,000 600 - 1,200 600 - 1,200
Range
miles miles miles miles miles
Moderate Moderate Moderate Moderate
High (50-100
Maintenance (100-200 (100-200 (100-200 (100-200
hours)
hours) hours) hours) hours)
Torque
Good Moderate Good Good Good
Characteristics
Emissions Moderate Higher Moderate Moderate Moderate
 Page 19

2) Comprehensive comparison of turboprop, turboshaft, and propfan aircraft engines-

Parameters Turboprop Turboshaft Propfan

Uses gas turbine to drive Powers helicopter rotors Drives large propellers using
Process
a propeller. via a shaft. jet-like engine.
Compact for aircraft
Shaft drive optimized for Open rotor design for high
Design integration with gearbox
rotor flow. speed efficiency.
and propeller.
Fuels Used Jet A, Jet A-1. Jet A, Jet A-1. Jet A, Jet A-1.
Typical range: $500,000 Varies by application, Can be $1 million+, depends on
Initial Cost
- $2 million. generally $300,000+. technology.
Overall 30-40% thermal Expected to exceed 45%,
Approximately 30-35%.
Efficiency efficiency. though varies with speed.
Varies by load, often 0.4 - More efficient than pure
Fuel Efficiency 0.3 - 0.5 lbs/hp/hr.
0.6 lbs/hp/hr. turbojets, specifics vary.
500 - 4,500 shaft
Typically 300 - 5,000 Similar range can be higher for
Power Delivery horsepower (SHP)
SHP. advanced models.
common.
MTBF around 3,000 - High reliability with Growing reliability as
Reliability
10,000 hours. MTBF often 4,000+ hours. technology matures.
Performance at Propeller limits to Dependent on vehicle, not Designed for speeds up to 600
High Speeds approx. 450 mph. high-speed focused. mph or more.
Thrust-to- Engine-specific, often Expected higher, around 6-8,
Typically 3-5.
Weight Ratio lower due to design. balancing fan benefits.

Speed Max speeds up to 400- Rotorcraft limited by Capable of reaching near-jet

Capabilities 500 mph. design, not speed. speeds, around 600 mph.

Varies, rotor noise Mitigated in newer designs, 85-

Noise Levels 85-90 dB typical.
significant, 80-110 dB. 95 dB potential.

Moderate; controlled by High, especially at low Can be higher, but

Vibrations
damper designs. rotor speeds. aerodynamics reduce issues.

Cooling Passive airflow Effective but complex due Advanced materials improve
efficiency sufficient for cooling. to rotor setup. cooling capabilities.
Range varies, typically Not range-focused, based Efficient high speed extends
Range
1,000-1,500 miles. on helicopter use. range, often >1,500 miles.
Straightforward, $100 - Complex systems, often Higher costs, advanced tech,
Maintenance
$300 per flight hour. $200 - $400/hr. $250+ per hr.
Torque High torque, moderate Primary focus varies with High torque for acceleration,
Characteristics speed range. mission profile. balances speed.
Potentially higher in
Moderate, refined fuels Lower at speed, leveraging high
Emissions hover, moderate
lower emissions. speed and efficiency.
otherwise.
 Page 20

3) Comprehensive comparison of Turbojet, Turbofan, Turbo-ramjet, Turbo-rocket,

and Advanced Ducted Engine-

Advanced
Parameter Turbojet Turbofan Turbo-ramjet Turbo-rocket
Ducted Engine
Air intake, Propellant is
Similar to Combines jet
compression, mixed and Combines aspects
Process turbojet with and ramjet
combustion, burned with of various engines
fan addition processes
exhaust oxidizer
More complex Simplified for
Simple, axial Rocket nozzle Modular design
Design with bypass high-speed
flow for high thrust for flexibility
duct operation
Kerosene, Liquid oxygen Kerosene,
Kerosene, Kerosene,
Fuels Used aviation fuels, and fuels (RP- hydrogen,
aviation fuels hydrogen
biofuels 1, LH2) alternative fuels
Moderate to Variable,
Initial Cost Low Moderate High
high typically high
Overall High (30- Moderate (20- Very high (up High, depending
Low (25-30%)
Efficiency 40%+) 30%) to 90%) on design
Fuel Efficiency Low High Moderate Very high High
Bypass thrust Direct thrust, Instant thrust,
Power Variable based on
Direct thrust increases very effective high
Delivery mode
efficiency at speed acceleration
High, with Moderate,
High, proven Moderate to High, depends on
Reliability additional more complex
technology high design
complexity systems
Excellent Excellent
Performance Good to excellent,
Good Moderate (high-speed (designed for
at High Speeds variable
optimized) high speeds)
Lower than
Thrust-to- High (20:1 or Moderate to Very high
turbojet (5:1 High, variable
Weight Ratio more) high (50:1 or more)
to 10:1)
Speed Subsonic to Subsonic to Supersonic to Variable, often
Hypersonic
Capabilities low supersonic transonic hypersonic high
Moderate to Very low Low, designed for
Noise Levels High Moderate
low during flight noise reduction
Moderate to
Vibrations Moderate Low Low Low to moderate
high
High, via Variable,
Cooling
Low Moderate Moderate combustion designed for
Efficiency
process efficiency
Extended due Extended due to
Range Limited Limited Limited
to efficiency efficiency
Higher due to Low to
Maintenance Moderate High Moderate to high
complexity moderate
Torque
Low High Low High Variable
Characteristics
Higher due to Lower due to
Lower with Low, focus on
Emissions incomplete efficient Moderate
advanced fuels sustainable fuels
combustion combustion
 Page 21

4) Comprehensive comparison with data of Ram jet, Pulse jet and Scram jet engine-

Parameter Ramjet Pulsejet Scramjet

Air intake, compression, Air intake, compression via Air intake, supersonic
Process
combustion shock waves, combustion combustion
Complex, requires
Design Simple, no moving parts Simple, often tubular
precise airflow design

Fuels Used Kerosene, hydrogen Kerosene, aviation fuel Hydrogen, kerosene

Initial Cost Moderate Low to moderate High

High (up to 50% or

Overall Efficiency Moderate (25-40%) Low (10-20%)
more)

Fuel Efficiency Moderate Low High

Power Delivery Continuous thrust Pulsed thrust Continuous thrust

Reliability High Moderate Moderate to high

Performance at Excellent (subsonic to Moderate (subsonic to low

Excellent (hypersonic)
High Speeds hypersonic) supersonic)
Thrust-to-Weight
Moderate (5:1 to 15:1) Low (1:1 to 3:1) High (up to 30:1)
Ratio

Speed Capabilities Subsonic to hypersonic Subsonic to low supersonic Supersonic to hypersonic

Noise Levels Moderate High Moderate to low

Vibrations Low High Moderate

Cooling Efficiency Low Low Moderate

Extended (depends on
Range Limited Very limited
vehicle design)

Maintenance Low Low Moderate to high

Torque
Low Moderate Low
Characteristics
Higher due to incomplete Lower with efficient
Emissions Moderate
combustion combustion
 Page 22

CONCLUSION
Aircraft propulsion systems are essential for the operation of modern aviation, with
each engine type showcasing distinct characteristics designed to meet specific
operational requirements. The classification of propulsion systems—ranging from
turbojets and turbofans to ramjets, pulsejets, and scramjets—highlights the diversity
in design and application.
Turbojets offer high-speed capabilities, making them suitable for military aircraft,
while turbofans dominate the commercial aviation sector due to their superior fuel
efficiency and lower noise levels. Ramjets and scramjets push the boundaries of
speed, with the latter designed for hypersonic flight, showcasing the potential for
future aerospace advancements. Pulsejets, though simple and inexpensive, find
limited application due to their inefficiencies and noise output.
The comparative analysis of these engines underscores the importance of selecting the
appropriate propulsion system based on specific mission requirements, including
performance, efficiency, and environmental considerations. As the aviation industry
evolves, ongoing innovations in engine technology and a shift towards sustainable
practices will continue to influence the development and implementation of aircraft
propulsion systems. The future of aviation depends on leveraging these advancements
to address the challenges of a rapidly evolving world, all while prioritizing safety,
efficiency, and minimizing environmental impact.

REFERENCES
1. https://en.wikipedia.org/wiki/Steam-powered_aircraft
2. https://www.stirlingengine.com/
3. learninglab.si.edu
4. https://www.britannica.com/technology/gas-turbine-engine
5. https://aerospaceengineeringblog.com/jet-engine-design/
6. https://www.researchgate.net/figure/Fig1-7-Low-Bypass-Ratio-vs-High-Bypass-
Ratiocourtesy-of-NASA-GRC_fig5_321802051
7. https://www.researchgate.net/figure/Thermodynamic-stations-of-a-
ramjet_fig2_324421366
8. https://issuu.com/irjet/docs/irjet-v10i1103
9. https://www.researchgate.net/figure/Schematic-diagram-of-scramjet-engine-
structure_fig1_335164588
10. https://eaglepubs.erau.edu/introductiontoaerospaceflightvehicles/chapter/electric-
aircraft/
11. https://youtube.com/playlist?list=PLIM1_UV2mR_O9ZZCwYoE8aSxQ5pBbohu
h&si=vSN8XWjBjCJCrNzS
12. Aircraft propulsion system by Saeed Farokhi-Second edition John Wiley & Sons
Ltd

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