SSME is really a turbo-jet engine and other trivia and questions

[Keatah]

The SSME's are really considered big-ass jet engines, with even bigger afterburners.

Consider that all the action happens within the turbine pumps and pre-burners and gas generators and all that. This turbine makes 6000psi of pressure and a fuel vapor that has already been ignited and exploding and on fire way before it hits the final combustion chamber. This is called staged combustion.

Just like a jet engine with an afterburner, the SSME is a turbine that blasts out hot flaming gasses which are further ignited and exploded in the final stage - AFTERBURNER!

So really, the final combustion chamber a monster-sized afterburner!



One other bit of trivia, the SSME controller is based on the venerable 68000 CPU, good enough.. But they paired that modern piece of silicon with plated wire memory!!

Core memory with a modern microprocessor! Pretty slick eh?
[ame="http://en.wikipedia.org/wiki/Space_Shuttle_main_engine"]Space Shuttle main engine - Wikipedia, the free encyclopedia[/ame]

 

[Loru]

No!
Jet engine takes oxidiser from atmosphere while SSME from internal LOX tank. It's rocket engine. Period

But there are lot similarities between turbojets and rocket engines with preburners.

 

[Keatah]

It's those similarities I was getting at.

 

[agentgonzo]

There are lots of similarities between a fiat panda and a formula 1 car (4 wheels, internal combustion engine etc) so a fiat panda is really a formula 1 car

 

[Keatah]

What I always find interesting is why combustion gasses don't explode back up through the injector pipes and blow the whole engine to smithereens.

---------- Post added at 06:14 AM ---------- Previous post was at 05:55 AM ----------

There are lots of similarities between a fiat panda and a formula 1 car (4 wheels, internal combustion engine etc) so a fiat panda is really a formula 1 car

A fiat is a fiat, and a formula 1 is a formula 1; both are internal combustion powered in principle and practice.

Here, we have a space shuttle main engine with a jet-powered powerhead - look at the schematic. The powerhead doesn't care where it gets the fuel and oxidizer from: from the atmosphere or a tank. It's all the same it comes from the atmosphere to begin with.

And this powerhead basically feeds an afterburner. This afterburner is little different in principle than an f100-pw-200e..

 

[Cras]

Rockets are a type of jet engine. It is not a turbo fan jet engine like you would find on a jetliner, but it is still a jet engine nonetheless.

 

[T.Neo]

No, a rocket engine is not a jet engine, it is a rocket engine. :facepalm:

The only rocket engines that could be considered jet engines, are ones that are hybridised with an airbreathing system, such as the SABRE engine proposed for Skylon.

Some of the physical concepts between a jet engine and a rocket engine might be similar, but they are most definitely not the same thing.

 

[Urwumpe]

Both SSME and Turbojet are fine pieces of turbo-machinery, but not of the same kind.

 

[n122vu]

When you're a Jet, you're a Jet all the way.

 

[T.Neo]

When all you have is a turbo, everything looks like a jet.

 

[Cras]

No, a rocket engine is not a jet engine, it is a rocket engine. :facepalm:

The only rocket engines that could be considered jet engines, are ones that are hybridised with an airbreathing system, such as the SABRE engine proposed for Skylon.

Some of the physical concepts between a jet engine and a rocket engine might be similar, but they are most definitely not the same thing.

Well, you are the first person I have ever come across to distinctly say that a rocket is in no way shape or form a jet engine.

So facepalm all you want, and in the typical fashion of this forum, we get into an argument it seems for the sake of getting into an argument.

The basic defination of a jet engine is: to utilize a reaction to generate a fast movine jet which can be directed out as thrust to then create propulsion via Newton's laws of motion. Now I admit that in the layman's terms, jet engines often are used to describe air breathing internal combustion engines, but that is short sighted. A jet engine does not require using air from the atmosphere.

Now if you were to say a Rocket Engine is not at all the same as a Turbo Fan, then I agree with you, and you and others have already proved this point fairly well, but most certainly a rocket engine, utilizing a chemical reaction to generate an explosion, which in turn is not allowed to spread in all directions but is forced out in the aft direction of the vehicle to create motion, certainly does fall into the general description of a jet engine.

 

[Urwumpe]

Well, you are the first person I have ever come across to distinctly say that a rocket is in no way shape or form a jet engine.

Then you know the wrong people it seems.

So facepalm all you want, and in the typical fashion of this forum, we get into an argument it seems for the sake of getting into an argument.

I think it is opposite, you defend a wrong definition here, see below:

The basic defination of a jet engine is: to utilize a reaction to generate a fast movine jet which can be directed out as thrust to then create propulsion via Newton's laws of motion. Now I admit that in the layman's terms, jet engines often are used to describe air breathing internal combustion engines, but that is short sighted. A jet engine does not require using air from the atmosphere.

You just wrote the minimal description of a rocket engine. Jet engines are by definition airbreathing. Turbojet engines are pretty much a special case of rocket engine, since they represent an airbreathing rocket engine that gets its propellant delivered by a gas turbine compressor.

But this isn't all: high-bypass turbofan engines for example are no longer this easy, since the fan isn't producing more of a jet as a propeller does. They get most thrust by the fan, not by the rocket engine like core.

What is the difference between a turbojet and an airbreathing rocket engine? From outside there is none. But internally, there is one big important one: The turbo jet gets the energy for its compressor from the exhaust flow, while rocket engines extract the energy before the combustion chamber.

If you try to design a turbojet engine, that represents this concept, you are already very close to the rocket engine. Next, your turbojet or rocket engine has to produce most compression by the compressor. Sounds simple, but that is the frontier to ramjets. A ramjet is a rocket engine that compresses the oxidizer by the inertia of the airflow.

An afterburning turbojet is another thing: It still produces in all but one exception more thrust by the turbojet core, than by the afterburner behind it. The exception is the engine of the SR-71. This produces at Mach 3 almost all thrust by the afterburner and actually gets more powerful at increasing speed, while the turbojet portion of the engine only exists at that speed to keep a low enough pressure behind the inlet for preventing inlet unstarts.

 

[T.Neo]

Let's solve this using the Internet;

[ame="http://en.wikipedia.org/wiki/Rocket_engine"]Rocket Engine[/ame], from Wikipedia:

A rocket engine, or simply "rocket", is a jet engine that uses only propellant mass for forming its high speed propulsive jet. Rocket engines are reaction engines and obtain thrust in accordance with Newton's third law.

And also [ame="http://en.wikipedia.org/wiki/Turbojet"]Turbojet[/ame];

The turbojet is the oldest kind of general-purpose airbreathing jet engine. Two engineers, Frank Whittle in the United Kingdom and Hans von Ohain in Germany, developed the concept independently into practical engines during the late 1930s.

Turbojets consist of an air inlet, an air compressor, a combustion chamber, a gas turbine (that drives the air compressor) and a nozzle. The air is compressed into the chamber, heated and expanded by the fuel combustion and then allowed to expand out through the turbine into the nozzle where it is accelerated to high speed to provide propulsion.

From [ame="http://en.wikipedia.org/wiki/Jet_engine"]Jet engine[/ame];

A jet engine is a reaction engine that discharges a fast moving jet to generate thrust by jet propulsion and in accordance with Newton's laws of motion. This broad definition of jet engines includes turbojets, turbofans, rockets, ramjets, pulse jets. In general, most jet engines are internal combustion engines[1] but non-combusting forms also exist.

And [ame="http://en.wikipedia.org/wiki/Airbreathing_jet_engine"]Airbreathing Jet Engine[/ame];

An airbreathing jet engine (or ducted jet engine) is a jet engine propelled by a jet of hot exhaust gases formed from air that is drawn into the engine via an inlet duct.

I this case I am not using the term "jet engine" to describe the physical concept, but rather an airbreathing jet engine, since Keatah is referring to turbojets specifically.

You can also say that the SSME is an 'internal combustion engine', as it runs on combustion occuring internally.

But it is most definitely not the same as a piston engine within a car, for example.

The SSME takes all of its reaction mass and all of its energy from an onboard source, which makes it a rocket engine. A jet engine gets a good deal of both chemical energy and reaction mass from an external source (the atmosphere).

And even though the SSME uses turbopumps, it does not use turbines in a manner similar to a jet engine. All turbojets (as far as I know) have their turbines aft of the combustion chamber; in other words, they take energy from their main propulsive stream.

You don't even need turbopumps to have a rocket engine. You can have a pressure-fed engine, and although it will have a lower chamber pressure and less performance, it will still be a rocket engine.

To mangle a quote by heart transplant pioneer Chris Barnard, the turbopump... is just a pump. An integral part of many engines, but not rocket engines as a whole.

 

[Hielor]

Let's solve this using the Internet;

Rocket Engine, from Wikipedia:



And also Turbojet;



From Jet engine;



And Airbreathing Jet Engine;



I this case I am not using the term "jet engine" to describe the physical concept, but rather an airbreathing jet engine, since Keatah is referring to turbojets specifically.

You can also say that the SSME is an 'internal combustion engine', as it runs on combustion occuring internally.

But it is most definitely not the same as a piston engine within a car, for example.

The SSME takes all of its reaction mass and all of its energy from an onboard source, which makes it a rocket engine. A jet engine gets a good deal of both chemical energy and reaction mass from an external source (the atmosphere).

And even though the SSME uses turbopumps, it does not use turbines in a manner similar to a jet engine. All turbojets (as far as I know) have their turbines aft of the combustion chamber; in other words, they take energy from their main propulsive stream.

You don't even need turbopumps to have a rocket engine. You can have a pressure-fed engine, and although it will have a lower chamber pressure and less performance, it will still be a rocket engine.

To mangle a quote by heart transplant pioneer Chris Barnard, the turbopump... is just a pump. An integral part of many engines, but not rocket engines as a whole.

You apparently ignored this part of the first article you quoted:

A rocket engine, or simply "rocket", is a jet engine that uses only propellant mass for forming its high speed propulsive jet.

 

[Urwumpe]

Hielor - but then, it is no turbojet engine.

 

[Hielor]

Hielor - but then, it is no turbojet engine.

It has turbos and is a jet engine, therefore, it's a turbojet engine? :lol:

 

[Urwumpe]

It has turbos and is a jet engine, therefore, it's a turbojet engine? :lol:

My mothers car has turbocharger and injection jets, is its engine now a turbojet engine? (and not a typical Diesel engine)

 

[Cras]

Hielor - but then, it is no turbojet engine.

If the argument is that a rocket is not a turbo-jet, then yes, I agree, and maybe that is where the topic should be about, since the original poster did mention turbo-jet.

I brought up the more general concept of jet engines, which rockets clearly fall under, but if we are to compare rockets, with turbo-jets, and even turbo-fans (which is what, I assume, usually pops into people's head when they hear the word "Jet" ), then they are truly different things, and not just because turbo-fans are air-breathing, but there is a different process altogether involved in the production of thrust.

So after all this we seem to have fallen prey to a debate about symantics, which is not at all as much fun as talking about rockets and turbo-fans, which since we are here posting on a forum dedicated to a space flight simulator, we all find more interesting.

 

[Keatah]

My mothers car has turbocharger and injection jets, is its engine now a turbojet engine? (and not a typical Diesel engine)

Absolutely not! The working gasses (when they combust and expand) push against machinery (enclosed cylinder chamber) that translates that into motion. The machinery is a piston/gearbox/tires. While there is some "action/reaction stuff" going on, it is negligible and does nothing to create thrust. The combustion energy is basically driving an infinite conveyor belt, the road and tire.

The turbo-charged automobile engine, again, does not use action/reaction like a jet/rocket does. Not unless you consider the powertrain as a reaction mass that is almost 100% efficient in its "transfer of friction" against the ground. Also consider that the fuel already on-fire as it enters the injector assembly.

You may argue the rocket engine also uses hot gasses pushing against machinery (the combustion chamber wall) that converts the combustion into motion. This is not the same as a car engine. The energy pushes the rocket directly, not conversion through a powertrain.

Perhaps it is best to consider the SSME as a turbo-powered afterburner. As the flames you see is basically a 2nd combustion stage. The first stage is in the pre-burner, which in and of itself produces a miniscule amount of thrust. The fuel is on fire already and explodes "full force" when "Afterburned" in the main combustion chamber and nozzle.

Consider this too, a car engine doesn't leave the reaction mass behind. It has no reaction mass to do so. In layman's terms, a rocket and jet engine leave behind a reaction mass that has "backward velocity" in relation to the propulsed vehicle.

Again, I say the SSME is a jet because of the turbine and pre-burner. I rather like the idea. And I also like to think true rocket engines are either SRB style with solids, or hypergolics, or simple pressurized tanks.

But put a turbine pre-burner in there and you have a tiny jet engine with a monster afterburner.

 

[T.Neo]

Can't we just call the SSME what it is? A staged-combustion rocket engine?

You apparently ignored this part of the first article you quoted:

My point still stands. An SSME is not an airbreathing jet engine, which is colloquially known as a 'jet engine'.