Juan David's Newsletter - August 14th, 2022
Types of Jet Engines
Morning,
My summer work ended this week and school starts in a couple of weeks. I will be doubling down on finishing the personal flying vehicle proposal (close to getting some grant money) as well as finishing the Venezuelan ambition platform.
Today I will spend the day reading all about flying vehicle to finalize calculations, costs, and designs. Then, I’ll put on my web designer hat and finish the platform.
I’m so excited!!!!!!
Today’s essay will be all about the TYPES OF JET ENGINES. If you haven’t read the essay on The Jet Engine, I’d recommend you start there.
Types of Jet Engines
This essay draft is part of an upcoming mega essay (or book) of an exploration of teaching myself EVERYTHING on Flying from Hidden History to Hardcore Engineering.
Imagine a machine that sucks air in, compresses it, burns the hell out of it, uses that energy to turn the turbine and fan, and then blows it out at really hot temperatures. That temperature difference is what produces thrust and the engineering behind the jet engine.
The jet engine is one of the most interesting, inspiring, and beautiful things I’ve learned recently. The engineering behind the jet engine is the best showcase of human triumph.
In this essay, we explore the different types of jet engines from how they work to how they are used.
Turbojets
The first and simplest type of gas turbine (aka jet engine) is the turbojet. The same principles apply. Air is taken from the front of the engine through the fan, which gets compressed to 3 to 12 times its original pressure. Fuel then is added to the air and burned in the combustion chamber to raise the temperature of the fluid mixture to about 1200 F. This air is hot and gets passed through a turbine, which drives the compressor and nozzle. For the nozzle, it gets its pressure to produce a fast stream of gas which produces what we want, thrust.
If you want to increase thrust by a large amount, you can implement the afterburner, which is a second combustion chamber that usually is placed after the turbine and before the nozzle. What the afterburner does is that it increases the temperature even more to about 2,540 F before it gets to the nozzle. The afterburner works by injecting fuel into a combustor right after the turbine, which reheats the air. Planes like fighter planes and The Concorde use the afterburner to fly faster than sound (supersonic). The disadvantage of the afterburner is that as you might expect it’s not fuel efficient as it burns much more fuel to produce greater amounts of thrust.
Turboprops
A turboprop engine is a jet engine attached to a propeller. This is what some small airliners and transport aircraft often use. This is how it works, the turbine at the back is turned by the hot gases, and this turns a shaft that drives the propeller.
There are two main parts to a turboprop propulsion system, the core engine, and the propeller. The core is similar to a basic turbojet but instead of using the energy from the hot exhaust through the nozzle to produce thrust, the turboprop uses most of the energy to turn the turbine.
The turboprop is pretty similar to the turbojet as it consists of pretty much the same components such as the compressor, combustion chamber, and turbine. An advantage of using a turboprop engine is the increased propeller efficiency below 500 miles per hour. This is because the turboprops have propellers that have a smaller diameter but a larger number of blades for efficient operation at much higher flight speeds. To be better suited for higher flight speeds, the blades have an interesting shape called scimitar-shaped (looking like a sword) with swept-back leading edges at the blade tips. Engines with such propellers are called propfans.
Turbofans
Alright now, let’s talk about the turbofan engine which has a large fan at the front, which sucks in the air. Most of the air flows around the outside of the engine, making it quieter and giving it more thrust at low speeds.
This is the most modern variation of the basic gas turbine engine. As with gas turbines, there is a core engine along with its parts. In a turbojet engine, all the entering air passes through the gas generator, which is composed of the compressor, combustion chamber, and turbine. In a turbofan engine, only a portion of the air goes into the combustion chamber. The rest of the air “bypasses” or goes through a fan (or low-pressure compressor) and is ejected directly as a “cold” jet or mixed with the gas generator exhaust to produce a “hot” jet.
The purpose of this “bypass system” is to increase thrust without increasing fuel consumption. This happens by increasing the total air-mass flow and reducing the velocity within the same total energy supply. A turbofan gets some of its thrust from the core and some of its thrust from the fan. The ratio of the air that goes around the engine to the air that goes through the core is called the bypass ratio.
Most of today’s airliners are powered by turbofans because of their high thrust and good fuel efficiency. The fuel flow rate for the core is changed only a small amount by the addition of the fan, a turbofan generates more thrust for nearly the same amount of fuel used by the core. This is what makes it very fuel efficient. Interestingly enough, high bypass ratio turbofans are nearly as fuel efficient as turboprops.
Want to know why turbofans are found on high-speed transports and why propellers are used on low-speed transport? THE FAN! Not you or me, we are just fans. I’m referring to the actual FAN! The fan is enclosed by the inlet and is composed of many blades, it can operate efficiently at higher speeds than a simple propeller.
Low bypass ratio turbofans are still more fuel efficient than a basic turbojet. Many modern fighter planes use a low bypass ratio turbofan equipped with afterburners. This allows them to cruise efficiently but still have very high thrust when dogfighting. Although fighter planes travel much faster than the speed of sound (supersonic), the air going into the engine must travel less than the speed of sound for high efficiency. Therefore, the airplane inlet slows the air down from supersonic speeds.
Turboshafts
The turboshaft is a variation of a jet engine that has been optimized to produce shaft power, instead of producing thrust. This one is interesting because it’s another form of gas-turbine engine and operates like a turboprop system. The difference is that it doesn’t have a propeller and instead provides power for a helicopter rotor. This engine is optimized to produce shaft power rather than jet thrust.
Turboshafts engines are mostly used in places where you need lots of power and reliability and where you don’t need to worry about big sizes or heavy weights. For example, helicopters, boats and ships, and hovercraft.
Ramjets
Now we get to the…RAMJET. This is the most simple jet engine and best of all? It has no moving parts. A friend recently pointed out that it’s funny how the ramjet mechanism for thrust is arguably much simpler than the slower-speed jet engine. Such is the nature of progress and the conquering of entropy.
The speed of the jet “rams” (forces) air into the engine to produce thrust. The ramjet produces no thrust when sitting still, which is why vehicles using a ramjet engine require assisted take-off to accelerate it to a speed where it begins to produce thrust.
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Ramjets are mostly used in guided missile systems and space vehicles. They are most efficient at supersonic speeds around Mach 3 (2,300 mph/3,700 kn/h) and can operate up to speeds of Mach 6 (4,600 mph/7,400km/h).
While ramjets work better at high speeds, their efficiency starts to drop at really high speeds because the air temperature in the inlet increases due to compression. If the inlet temperature gets closer to the exhaust temperature, there is not really much difference in temperature, which means less energy can be extracted in the form of thrust. So we have a problem but in reality, an opportunity.
To produce more thrust at higher speeds, the ramjet must be modified so the incoming air isn’t compressed (and heated) as much. This air coming in will be moving at supersonic speeds. Therefore, this engine modification is called the supersonic-combustion ramjet, or scramjet.
Taking Simple Inputs
We take inputs (air), we write functions (fan, compressor, combustor, turbine, nozzle, etc), and we get outputs (thrust). It turns out that aerospace engineering isn’t that different from computer science.
That only makes me wonder how you can make similar engineering inventions by taking simple inputs, writing complex functions, and getting unthinkable outputs.
Being curious is true happiness because it never runs out.
Next week, we’ll talk about the history of the Jet Engine.
or
Jenga is boring because it’s so repetitive. Instead of doing the boring Jenga, me and two co-designers built this structure using the Star of David as the base structure. More than beautiful!
And of course, a bunch of people started to look at us weirdly and confused. “That is not the purpose of the Jenga” “Just do it the normal way” “Bro, just why?” But I’ve learned to just look at them in their eyes and come from a place of understanding.
Ciao,
Juan David Campolargo