How Jet Engines Work

Summary

In 'How Jet Engines Work,' Jake O'Neal explains the turbofan design of modern jet engines, detailing their core components: the compressor, combustor, and turbine. The compressor increases air pressure, the combustor mixes air with fuel for powerful combustion, and the turbine powers the engine. Turbofan engines use bypass air for efficiency and noise reduction, while afterburners provide short bursts of extra power. This overview highlights the complexity and efficiency of jet propulsion technology.

Takeaways

• 🚀 Most jet-propelled airplanes use a turbofan design, which is a high-tech propeller inside a duct called a diffuser, driven by a gas generator.
• 🔧 The core of a jet engine is a gas generator that creates high-pressure gas to power a turbine, consisting of compressor, combustor, and turbine sections.
• 🌀 The compressor increases air pressure in stages, using a spinning rotor and stationary stator vanes to swirl and compress the air.
• 🔥 The combustor mixes air with fuel and ignites it, releasing a jet of super high-powered gas in an annular design for even mixing.
• 🌀 Turbines at the rear of the engine are powered by exhaust gases, with most power used to turn the fan and a smaller percentage for the compressor stages.
• 🔥 Turbine fins get extremely hot, requiring cooling from diverted compressor air and special coatings to manage temperatures.
• 🌪 The exhaust cone is specially shaped to mix and accelerate exhaust streams, also protecting sensitive internal engine parts.
• 🌬 Early turbojets had all air flowing through the core, but modern turbofans have a bypass system where only a fraction of air enters the core, with the rest powering a fan.
• 🛫 High bypass engines are designed for large quantities of air at slower speeds, suitable for commercial airliners and military transport aircraft.
• 🔊 Exhaust velocity affects jet engine noise; high bypass engines reduce noise by surrounding fast-moving core exhaust with slower-moving bypass air.
• ✈️ Military fighter aircraft use low bypass engines for compact size, high power-to-weight ratios, supersonic capabilities, and afterburners, despite noise and fuel consumption drawbacks.
• 🔥 Afterburners provide a second stage of combustion by igniting additional fuel mixed with exhaust gas, used for short bursts in high-performance engines due to fuel inefficiency.

Q & A

What is the primary function of a turbofan engine in a jet airplane?

The primary function of a turbofan engine is to provide thrust by using a high-tech propeller inside a duct called a diffuser, which is driven by a gas generator.

What is the core of a jet engine and what does it do?

The core of a jet engine is a gas generator that creates high-pressure gas to power a turbine, consisting of compressor, combustor, and turbine sections.

How does the compressor section of a jet engine work?

The compressor section works by compressing air in stages, forcing incoming air into increasingly narrow chambers with the help of spinning rotor blades and stationary stator vanes, which increase air pressure for more powerful combustion.

What is the purpose of the stator vanes in a compressor?

Stator vanes slow the swirling momentum of air from the rotor blades in exchange for increased air pressure, preparing the air for the combustion process.

How does the combustor section of a jet engine function?

The combustor section mixes compressed air with fuel and ignites it, releasing a jet of super high-powered gas that powers the engine.

What is an annular combustor and why is it used?

An annular combustor is a ring-shaped design that allows for an even mix of fuel and air, which is swirled and ignited by ignitor plugs for efficient and uniform combustion.

What is the role of the turbine in a jet engine?

The turbine in a jet engine is powered by exhaust gases from the combustor and uses much of its power to turn the fan, with a smaller percentage powering the compressor stages.

Why is cooling important for turbine fins in a jet engine?

Cooling is important for turbine fins because they get extremely hot due to the high temperatures of the exhaust gases, so air from the compressor is diverted for cooling, and special coatings are used to keep temperatures down.

What is the purpose of the exhaust cone in a jet engine?

The exhaust cone is specially shaped to mix and accelerate exhaust streams, and it also covers sensitive internal engine parts.

How does a high bypass engine differ from a low bypass engine?

A high bypass engine moves large quantities of air at slower cruising speeds for high efficiency and is larger with massive fans compared to core size, suitable for commercial airliners or military transport aircraft. A low bypass engine is more compact, has a high power-to-weight ratio, and can achieve supersonic speeds and afterburner capabilities, used in military fighter aircraft.

What is an afterburner and how is it used in jet engines?

An afterburner is a feature in high-performance engines that allows additional fuel to be sprayed into a jet pipe section, mixed with exhaust gas, and ignited for a second stage of combustion. It is generally used in short bursts during takeoff, climb, or combat maneuvers due to its fuel inefficiency.

Outlines

00:00

🛩️ How Jet Engines Work - Turbofan Design

Jake O'Neal introduces the fundamental concept of jet engines, focusing on the turbofan design used in most modern aircraft. He explains the turbofan as a high-tech propeller within a diffuser, driven by a gas generator. The core of the jet engine is described as a gas generator that produces high-pressure gas to power a turbine, which consists of a compressor, combustor, and turbine sections. The compressor stage is detailed, highlighting its role in increasing air pressure for more powerful combustion.

🔧 The Anatomy of a Jet Engine's Core Components

This section delves deeper into the jet engine's core components, starting with the compressor, which is responsible for compressing air in stages to enhance combustion efficiency. The role of rotor blades and stator vanes in air compression is explained, along with the distinction between low and high-pressure stages. The combustor's function in mixing air with fuel and igniting it to release high-powered gas is covered, with an emphasis on the annular combustor design. The turbine's role in harnessing exhaust gas to power the fan and compressor is also discussed, including the use of cooling techniques for turbine fins.

🌀 The Function of the Fan and Bypass Air in Jet Engines

The evolution from turbojets to turbofans is outlined, explaining how modern engines use a fan to handle a portion of the incoming air, while the rest bypasses the core. The benefits of high bypass engines in terms of efficiency and quieter operation are highlighted, along with their applications in commercial and military transport aircraft. The trade-offs of engine size and noise control are discussed, as well as the role of exhaust velocity in jet engine noise.

✈️ Military and Civilian Applications of Jet Engines

This paragraph contrasts the use of low bypass engines in military fighter aircraft, which prioritize compactness, high power-to-weight ratios, and supersonic capabilities, with the high bypass engines used in commercial airliners for their efficiency and noise reduction. The challenges of noise control and fuel consumption associated with military engines are noted, as well as the advantages of high bypass engines for civilian use.

🔥 Afterburners and Exhaust Nozzles in Jet Engines

The capability of afterburners in high-performance engines is explored, describing how additional fuel is ignited in the jet pipe to produce a second stage of combustion, resulting in a significant thrust increase. The use of afterburners is typically limited to short bursts due to their fuel inefficiency. The adjustable exhaust nozzle is also discussed, explaining its role in maximizing exhaust acceleration and avoiding back-pressure that could damage engine components.

Keywords

💡turbofan

A turbofan is a type of jet engine that uses a ducted fan to provide most of the thrust, in addition to the thrust provided by the core engine. It is central to the video's theme as it describes the modern design of jet engines used in most aircraft. The script mentions that 'Most modern winged aircraft engines are turbofans, where only a fraction of air enters the core,' highlighting its prevalence and function in aviation.

💡gas generator

The gas generator is the core component of a jet engine that generates high-pressure gas to power a turbine. It is integral to understanding the video's theme as it explains the fundamental process of jet propulsion. The script describes it as 'a high tech propeller inside of a duct called a diffuser, driven by a gas generator,' indicating its role in the compression and combustion stages.

💡compressor

A compressor is a device that increases the pressure of the air entering the engine. It is key to the video's narrative as it sets the stage for the combustion process. The script details that 'Compression happens in stages that force incoming air into an increasingly narrow chamber,' showcasing its function in preparing the air for the next stages of the engine cycle.

💡combustor

The combustor is the part of the engine where air is mixed with fuel and ignited, releasing a high-powered gas jet. It is a critical concept in the video as it explains the energy conversion process in jet engines. The script describes an 'annular combustor,' which is 'ring shaped,' and explains the even mixing and ignition process within it.

💡turbine

A turbine is a device that extracts energy from a flowing fluid and converts it into mechanical work. In the context of the video, turbines are powered by exhaust gases and are essential for turning the fan and compressor. The script notes that 'Turbines at the rear of the jet engine are powered by exhaust gasses exiting the combustor,' illustrating their role in the engine's operation.

💡bypass air

Bypass air refers to the air that does not enter the core of the engine but is instead redirected around it. This concept is important to the video's theme as it differentiates high bypass engines from other types. The script states that 'Air that does not enter the core is called bypass air,' and explains the design implications for high bypass engines.

💡high bypass engine

A high bypass engine is designed to move large quantities of air at slower speeds, sacrificing size for efficiency. It is a significant concept in the video as it contrasts with low bypass engines. The script mentions that 'High bypass engines are designed to move large quantities of air at slower cruising speeds,' and gives examples of commercial airliners using such engines.

💡exhaust velocity

Exhaust velocity is a measure of how fast the exhaust gases are expelled from the engine, which is a major factor in jet engine noise. It is relevant to the video's theme as it discusses the acoustic implications of different engine designs. The script explains that 'Exhaust velocity is a major factor in jet engine noise,' and how high bypass engines mitigate this with slower-moving bypass air.

💡afterburner

An afterburner is a device that increases thrust by adding additional fuel to the exhaust gases, creating a second stage of combustion. It is a key concept in the video as it discusses high-performance capabilities of certain engines. The script describes that 'High performance engines may have afterburner capability,' and notes its use in 'short bursts during takeoff, climb, or combat maneuvers.'

💡exhaust nozzle

The exhaust nozzle is the part of the engine that controls the direction and speed of the exhaust gases. It is important to the video's theme as it discusses the optimization of engine performance. The script mentions that 'The exhaust nozzle is adjustable for maximum exhaust acceleration,' and its role in avoiding back-pressure.

💡compressor stages

Compressor stages refer to the sequential steps in which air is compressed within the engine. This concept is fundamental to the video's theme as it explains the process of air compression. The script specifies that 'This compressor has four low pressure and ten high pressure stages,' detailing the multi-stage compression process.

Highlights

Introduction to the turbofan design as the most commonly used jet propulsion system in airplanes.

Explanation of the turbofan as a high-tech propeller within a diffuser, driven by a gas generator.

Description of the core of a jet engine as a gas generator that creates high-pressure gas to power a turbine.

Details on the compressor section, which includes multiple stages for air compression.

Role of rotor blades and stator vanes in the compressor for air swirling and pressure increase.

Specification of the compressor's four low-pressure and ten high-pressure stages.

Process of air and fuel mixing and ignition in the annular combustor.

Design of the combustor with inlet nozzles and fuel injectors for an even fuel-air mix.

Functioning of ignitor plugs in the combustor for initiating and sustaining combustion.

Role of the turbine in the jet engine, powered by exhaust gases from the combustor.

Mechanism of turbine power distribution between the fan and compressor stages.

Importance of cooling in turbines and the use of special coatings to manage high temperatures.

Explanation of the exhaust cone's role in mixing and accelerating exhaust streams.

Difference between early turbojets and modern turbofans, particularly the use of bypass air.

Advantages of high bypass engines in terms of efficiency and size for commercial and military applications.

Impact of exhaust velocity on jet engine noise and how high bypass engines mitigate it.

Characteristics of low bypass engines used in military fighter aircraft for high performance.

Functioning and purpose of afterburners in high-performance engines for short bursts of power.

Adjustability of the exhaust nozzle for optimal performance and to prevent back-pressure.

Transcripts

I'm Jake O'Neal, creator of Animagraffs, and this is

How Jet Engines Work

Most jet propelled airplanes use a turbofan design.

The turbofan can be thought of as a high tech propellor inside of a duct called a diffuser,

driven by a gas generator.

The Core

The core of a jet engine is a gas generator that creates high pressure gas to power a

turbine.

This setup has compressor, combustor, and turbine sections.

The Compressor

Compressed air makes for a much more powerful combustion reaction relative to engine size.

Compression happens in stages that force incoming air into an increasingly narrow chamber.

A single compressor stage is comprised of a spinning rotor paired with a ring of stationary

stator vanes which are attached to the core casing.

Rotor blades swirl the air as they force it through the compressor.

Stator vanes slow this swirling momentum in exchange for increased air pressure.

This compressor has four low pressure and ten high pressure stages.

The Combustor

Air is mixed with fuel and ignited as it passes through the combustor, releasing a jet of

super high powered gas.

The design shown here is an annular combustor, meaning "ring shaped."

Compressed air enters the inlet nozzles.

Each nozzle is coupled with a fuel injector, and is designed to swirl the incoming fuel

and air for an even mix.

A couple of ignitor plugs, not unlike the spark plugs found in car engines, ignite this

mixture and the reaction spreads evenly around the ring.

Once started, combustion continues as long as air and fuel are supplied.

The turbine

Turbines at the rear of the jet engine are powered by exhaust gasses exiting the combustor.

Much of the turbine power is used to turn the fan while a smaller percentage powers

the compressor stages.

Turbine fins get extremely hot.

Some air from the compressor is diverted for cooling, and special coatings are used to

keep temperatures down.

The exhaust cone is specially shaped to mix

and accelerate exhaust streams.

It also covers sensitive internal engine parts.

The fan

Early jet engines were turbojets, where all incoming air flows through the core.

Most modern winged aircraft engines are turbofans, where only a fraction of air enters the core

or gas generator, and the resulting power turns a specially designed fan.

Again, the fan can be thought of as a high-tech propeller inside of a duct.

Air that does not enter the core is called bypass air.

High bypass engines are designed to move large quantities of air at slower cruising speeds

(a range of about 310 to 620 mph).

The exchange for high efficiency is engine size – high bypass engines can be very large,

with massive fans compared to core size.

Commercial airliners or military transport aircraft are example applications.

Exhaust velocity is a major factor in jet engine noise.

High bypass engines surround fast-moving core exhaust with large quantities of slower-moving

bypass air for quieter operation.

Military fighter aircraft use low bypass engines, which are more compact, have high power-to-weight

ratios, plus supersonic and afterburner capabilities, in exchange for things like poor noise control

and high fuel consumption.

Afterburner

High performance engines may have afterburner capability.

Additional fuel is sprayed into a jet pipe section where it mixes with exhaust gas, and

is ignited, producing a second stage of combustion.

Since afterburner is fuel inefficient, it's generally used in short bursts during takeoff,

climb, or combat maneuvers.

The exhaust nozzle is adjustable for maximum exhaust acceleration and to avoid undesirable

back-pressure which can harm forward engine parts.