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Auto-Cross Addict
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Discussion Starter #1
So at the constant bugging of Zoni, I'm posting this to help out people on better understanding turbochargers. This is a very basic version.

This is a cut-away of a tubro charger:


As you can see, the turbocharger is composed of two turbines. On the left side is the air intake. As you can tell from the burnt coloring, the right side is the exhaust side. The two are seperated to prevent mixing of exhaust and fresh air.


Intake:


The intake turbine pulls in clean air by creating a suction pull. The air is forced through a smaller opening than would be adaqute for normal air pressure. By doing this, it cause pressure to build and thus, forcing more air into the engine then would normally be taken in. The air then travels through an aftercooler (which can be either air-to-air, or air-to-water) and into the engine.


Exhaust:


The exhaust turbine is spun by the exhaust gases being forced out of the engine. The turning of the exhaust turbine causes the the intake turbine to spin also. And that is how the intake suction is created.

Anyone can feel free to add in more.
Hope this enlightened you a little:)

-Mike Brausen
 

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Auto-Cross Addict
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Discussion Starter #3
Thanks a lot Eric! I forgot to add that link at the bottom of my post.

For detailed information, go to the link posted above.
 

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Trailer Trash Engineer
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592 Posts
Nice pics. Good basic description. I have one minor point to expand upon.
The intake turbine pulls in clean air by creating a suction pull. The air is forced through a smaller opening than would be adaqute for normal air pressure. By doing this, it cause pressure to build and thus, forcing more air into the engine then would normally be taken in.
What happens is based on the same principle that allows an airplane to fly and a carburetor to work. As air speeds up, pressure drops and as it slows, pressure builds. The compressor draws in air and flings it outward through a slot in the snail at a very high speed. Since it is flung out at high speed and low pressure, the wheel can draw in more volume than the engine displaces. Once through the slot, it then slows down in the increasing diameter of the snail body until it reaches the exit point. It is in this slowing down of the air that it builds pressure or "boost".
If the engine isn't consuming enough air, or the turbo is too big, the turbo can go into surge where it becomes unstable. This can cause spikes and sags in the boost at the least, and destroy the turbo and the engine at the worst, should pieces of the wheel wind up in the cylinders.
If the turbo(or compressor wheel) is too small, or the engine is consuming too much, the turbo has to spin faster and faster to supply the required boost and becomes inefficient and generates too much heat to be practical. In fact, it can be counter productive.
And that's just on the compressor side. The turbine is another whole story by itself.
 

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Auto-Cross Addict
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Discussion Starter #5
Thanks! Always love added information. I'm hoping people will keep adding, help out anyone new to F/I.

And I was keeping mine as simple as possible. As I pointed out, I was being pushed to post it:)

Keep the info coming!
 

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"I BUILD SLEEPERS"
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2,558 Posts
posted by SmokingTiresV6
As you can see, the turbocharger is composed of two turbines
It not 2 turbines... a turbine has always work under a exhaust ... the intake side is called a compressor and the exhaust side is called a turbine...

posted by alltrac165

a slot in the snail at a very high speed
its called the Volute...
 

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Trailer Trash Engineer
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592 Posts
SmokingTiresV6 said:
Thanks! Always love added information. I'm hoping people will keep adding, help out anyone new to F/I.

And I was keeping mine as simple as possible. As I pointed out, I was being pushed to post it:)

Keep the info coming!
Oh, yeah, simple....
I'm not very good at simple...
I'm really good at complicating things so much that even I don't get it after a while...:p:
 

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Trailer Trash Engineer
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FALCON2691 said:
alltrack, i see alot of good information...what do you do for a job if you dont mind me askin.
I'm an electrical contractor, actually. I have always had a passion for engines, though, and work part time with a friend of mine at a head porting, thermal coating, and race engine shop.
 

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ASE Master, now Realtor
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368 Posts
It's good to see a sticky on this. It was also good to see a cutaway from a Mack truck engine turbo. I once worked in a shop (or three) that repaired trucks. Déjà vu.

The reason we use turbos is twofold.

Here at sea level, we use turbos to increase the "volumetric efficiency" of an engine. In other words, by forcing more air into an engine we can also add more fuel, and so we can get more power from an engine by making its combustion "volume" more "efficient." We can moderate the boost by controlling the amount of exhaust gas volume entering the turbine wheel by means of a "waste gate." The exhaust we don't need can be "wasted" by this controllable valve, sending it around to bypass the turbo and on into the exhaust system.

The other reason we use turbos is to maintain power. In many reciprocating aircraft engines, turbos are used to provide enough boost to maintain the power output of an engine running at sea level as the aircraft climbs in the atmosphere, where the air becomes progressively thinner. Aviation calls this “Turbonormalizing.”

Things to know: turbos spin incredibly fast, on the order of 20,000 rpm and more. They need air that is very clean, because particles of dirt can wear the compressor fins, and you don't want to be packing dirty air into an engine.

Turbos also need oil, and lots of it. Many turbo applications use a shutdown oil pump, designed to maintain oil pressure and oil flow to the turbo's bearings to carry away heat after shutdown. This really extends the life of a turbo, and as some of you know, they are not cheap to replace.

The same pump is often used as a "pre-luber," designed to supply oil pressure to every bearing in the engine and the turbo BEFORE it is faced with the loads of starting and initial running. This practice of pre- and post- lubricating extends the life of both the turbo and the engine it serves. If you want more miles out of a turbocharged engine, or if you want to extend the life of a supercharged engine, a lube pump is a great way to go.

One factor that shortens the life of a turbo is the level of maintenance the engine receives. I have seen blocked oil passages due to infrequent oil changes, leading to a total failure of the "center section" of a turbo. The center section is the part with the shaft, the wheels, and the bearings. The center section lives in the compressor and turbine shells or "snails," as described above.

Now for the downside. We pay a price in engine life, even with extra lubrication, when we increase the volumetric efficiency of many engines. Most of this is due to the increased power being produced by an engine that was not originally designed to be turbocharged, and the other factor is heat. The engine bay of a Mack or Freightliner is huge, and there is a massive, I mean REALLY massive radiator and intercooler there to keep heat at bay. In a Camry or other auto engine, we have a cramped space with few choices for dealing with heat. Why is that bad?

First, heat is created whenever we compress a gas, and in terms of physics, atmospheric air is a combination of gasses, mostly nitrogen. Engines don’t like hot air, which is why you see “cold air intake” kits for sale. Cooler air is more dense than warm air, and therefore has more oxygen per unit volume to support combustion. So, once we compress the air, we need to get rid of that heat so the air entering the engine will be more dense. An intercooler, either air-to-air or air-to-water is how we do that. Engines run better on cool, dense air. Drag racers want a low “density altitude” for their runs, a factor that encompasses both air temperature and pressure. So, getting the compressed air coming from the turbo to get “cool” is a priority for the best efficiency and the highest performance, here on earth or in the sky.

Second, if the engine was not specifically designed to be turbocharged, that engine will be challenged to deal with the additional stress and higher temperatures not faced by its normally aspirated cousin. In fact, even if it was designed to receive boost, the engine will not live as long without a rebuild. For example, a typical small aircraft engine will last around 2,000 hours of running time. When it is turbocharged, the same engine will be expected to be serviceable for several hundred hours less.

So:

Clean air in

Lots of oil

Cool the air

Watch engine heat

Consider pre- and post- lubrication.
 
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