Turbocharger and Its Use

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Turbocharger - Wikipedia, the free encyclopedia

Turbocharger and its use

It increases the volume of fuel/air that is introduced into the cylinder of an engine, allowing the engine to produce more power than if not turbocharged.

They can increase fuel efficiency, also, under the right conditions.

Dear Mecsoccer,

The diesel burning requires excess air for proper combustion and release the Heat Energy. Natual Suction of the air for combustion in to the cylinder at high piston speeds, the air will not be sufficient asper STOICHOMETRIC equation.

To suck more air, the turbo charger is used - driven by the Exhaust Gas Heat, thus, the waste heat is partly used, to pump more air in to the cylinder.

About 3 decades back, SUPER CHARGER was used to pump more air in to the cylinder, which was using the Mechanical Energy from the Engine, through Belt Drive, consuming the Mechanical Energy from the engine.

Turbo-Charger is more efficient than Super Charger, but MAINTANANCE SHOULD BE MORE PRECISE, as its speed will be around 2,00,000 to 2,40,000 (2.0 Lakhs to 2.4 Lakhs) R.P.M, where as SUPER CHARGER speed was 2400 to 3000 R.P.M.

DHAYANANDHAN.S.

"To suck more air, the turbo charger is used - driven by the Exhaust Gas Heat, thus, the waste heat is partly used, to pump more air in to the cylinder."

Not quite. It is the kinetic energy, not the thermal energy, of the exhaust gas which drives the turbocharger. The exhaust gas is piped through a turbine which drives the compressor of the turbocharger.

http://www.howstuffworks.com/enlarge-image.htm?terms=turbocharger&page=2

Dear Mr.php001,

You are right. But it is the kinetic energy + the heat energy combination, the- gas turbine part rotor works like a regular gas turbine which inturn rotates the blower part on the other side of the shaft, which inhales atmospheric air and sends to Engine.

Whatever Thermodynamic Equations apply for regular and big gas turbine applicable, IS APPLICABLE TO THIS TURBO-CHARGER ALSO, only Difference is size is small and speed is very high.

DHAYANANDHAN.S

Sorry, I'm afraid you still have not got it quite right. In the gas turbine, as as in the turbocharger, it is only the flow of gas, the kinetic energy, which drives the vanes of the turbine. The reason why the gas is hot in the gas turbine is because it has been heated to increase its volume, and thereby the flow. The fact that it is hot when it hits the turbine blade does not make it any more effective. Indeed the transfer of heat to the turbine blade is a real headache in the design and construction of the blade.

And, hot air is less dense, so less work is done compared to the same volume of cold air.

A petrol engine can use natural aspiration that is it sucks the air it needs when the piston goes down. As the air is drawn in so a small amount of petrol is injected. This is compressed and then ignited.

A turbo has 2 small fans on a common shaft. One fan is in the path of the engine exhaust. AS the engine is rev-ved so this fan turns. The other fan is used to compress the air flowing into the engine - more air and petrol mix is forced in.

Like any fan the turbo falls the fan laws so on a car engine really only kicks in at about 3000 rpm. The turbo itself rotates far more quickly - likely 100,000 rpm. Its only a small diameter shaft so radial speed is not excessive.

The advantage is you can get more power out of a smaller lighter weight engine.

Well, the engine doesn't suck air. Air is pushed into the cylinders by atmospheric pressure.

A turbo pushes more air into the same space in the cylinder.

Small point, but...........................

Yes - the engine sucks air. The inlet manifold ha a slight vacuum on it. Take the air filter off and listen with a hose near to the carb inlet - you will hear it sucking.

The only reason atmospheric pressure will push air into somewhere is if that somewhere is at a slight vaccum. So thats like the engine sucking .....

The vacuum on the inlet manifold was used by some old Fords to power the windscreen wipers.

Sorry. That was incorrect. At least it as I see it.

The sound you hear at the intake of an engine is the air rushing into the cylinder, being pushed by 14.7 pounds per square inch of air above the ground.

The wiper vacuum motor was driven by atmospheric pressure. As the accelerator is pushed down/open, the pressure difference between inside and outside the motor goes away and the wipers quit working. Till you took your foot off the accelerator.

Then, they flap like crazy.

For a complete synopsis you will compare a naturally aspirated engine to a turbo charged engine. Normal aspirated engine has four strokes normally. Intake, compression , power and exhaust. Only the power stroke produce power the other three are necessary but only contribute to the overall system. The compression and exhaust as well as the intake consume part of the power generated.

With a turbo charger the exhaust gas when forced out past the exhaust valve spins a turbine that is connected to a compressor turbine. The compressor draws in air and compresses it and forces it into the cylinder actually overcoming the negative pressure of a natural aspirated condition and in high pressure conditions contributes to forcing the piston down the cylinder resulting in a second power stroke. As well as contributing to added air volume along with added fuel you tend to get higher efficiency since you are taking waste exhaust and having it perform a useful function. At this time you have three strokes performing something useful with only the compression stroke using part of the produced power. It is important that the turbo be as close to the exhaust valve as possible since the heat contained in the exhaust contributes to the volume of gas that is required to spin the turbocharger. Any heat lost between the exhaust valve and turbo will reduce overall efficiency.

You will have to adjust timing events and cool the intake air in most cases to prevent detonation and pre ignition that can destroy an engine. This is quite simplified but contains the facts.

This is all a bit mixed up. A 4 stroke engine and a turbo blown 4 stroke engine are one and the same thing. You can also get a turbo scavanged 2 stroke where the turbo is used to draw the exhaust gases out. Every stroke takes power out of the system. Even the power stroke will not be able to convert all of the chemical energy into mechanical energy. There will be losses such as heat. It has nothing to do with pushing the piston down the cylinder. The turbo causes more fuel (petrol and air) to be forced into the cylinder. THe more the fuel the bigger the bang and the more power from the engine. Second power stroke - hope to god you don't work on cars! Your post is pure nonsense. Suggest you go to a library and get a book on car engines - your time will not be wasted.

It is sad that your feel compelled to contradict the facts. I did not mention two stroke in order to simplify the topic. If for one minute you do not feel that any positive pressure can push down the piston on an engine then stay away from all positive pressures. Some of the OTR turbo charged diesels I worked on produced 45 PSI at the intake valve. Before they changed the rules some Indy engines were up to 95 PSI. the F1 were higher again. Should you think for one second that 95 or even 45 psi means nothing to the top of a piston in potential work shame on you. I also realize that production cars rarely get above 15 PSI intake pressure and more than likely only 3-10 due to restraints. 4x4 inch bore = about 12 sq inches --do the math. Unlike you for obvious reason I have 30 successful years on all types of piston engines. Just for information a normally aspirated engine under full throttle can have up to about 1200 PSI on the top of the piston. A turbo diesel may experience about 2400 PSI and the majority of steam locomotives pulled miles of cars at 200 PSI. Pressure is pressure and can do work.

unless that pressure at the valve actually hits the top of the piston it will do nothing.

4 stroke engine, the intake valve only opens once per cycle so how exactly does this high pressure air get to the piston during anything but the intake stroke??

That exactly is the stroke we are talking about. Instead of the piston creating a negative condition for air flow as in normally aspirated engine the compressed air first will create a balanced condition and if enough pressure is present in the compressed intake charge it will assist in forcing the piston down. You see first we get rid of parasitic losses of creating a vacuum on that stroke and benefit of the compressed air energy. Of course this is done in different degrees pertaining to the design of the engine. EG. 10 PSI on a 12 sq. in. piston will give about 120 lbs of force or push. v/s having to pull the air in to the cylinder. 45 psi on same piston will give approx. 540 lbs of force or push. As mentioned out of the four strokes (1) intake is producing some work, (2) exhaust is providing a useful function in powering the turbine and the (3) power stroke is providing greatly enhanced power. (4) Only the compression stroke is a parasite. Then again the air & fuel must be compressed so it is an acceptable parasite.

Still here and still contradicting facts?

I agree pressure on a piston will cause it to move. Strange they didn't use these turbo things in steam locomotives though.

The turbo takes energy from the exhaust from one impellor and with the other causes a pressure. There will be less pressure pushed into the engine than you are taking out from the exhaust. Energy will be lost - its is not 100% efficient.

That pressure is all about pushing explosive gases into the engine. The % of it that wuld be push the piston down is almost negligible. Think it through unless of course you don't think petrol adds much to what goes on.

Have you noticed a turbo blown car is more powerful than naturally aspirated. Have you noticed they use more fuel. Have you wondered where the power comes from. This is a no brainer.

Atmopsheric pressure will only flow into something if its empty. Its called a vacuum. You create the vacuum when the piston decends. It sucks!

Atmopsheric pressure will only flow into something if its empty. Its called a vacuum. You create the vacuum when the piston decends. It sucks!

LYN has, in his post, addressed the idea of a vacuum. It doesn't exist. At least not in the way most people, including yourself, think it does. The word describes a condition that can be best described as any pressure less than 103 KPa ( 14.7 psi ). Notice that a pressure of 80 KPa is still a pressure. Air will flow from an area of high pressure to an area of lower pressure, it does not get sucked in. Sure, in terms of language and the ability to convey a concept, the words suck and suction are very valuable but in the science area it it misguiding, leading to incorrect concepts and misunderstanding.

Planes that use piston engines and fly high where the air pressure is low have to have a means of increasing air flow to give the combustion process enough oxygen. Although oxygen is the main ingredient required an injection of oxygen alone would cause the engine to melt. NOX is one way to to add extra oxygen without an instant meltdown, but even then... So a better way is to increase the inlet pressure to achieve higher flow rates. Way back in 1902 Louis Renault grasped this concept and put a 'fan' onto the intake of his engine to assist with the airflow. Was it a turbo ( turbine ) or a supercharger? I don't know.

To DHAYANANDHAN.S. check the current MERCEDES lineup. You will see many models with the KOMPRESSOR name plate. These are supercharged. It is still in use.

Then there is the debate about which is better.

turbocharger. Which inadvertantly heats the air expanding it and making it less dense thereby creating less pressure than could otherwise be achieved.

turbocharger with intercooler. to try to overcome the above problem.

supercharger. Which uses front end engine power to drive it, but produces cooler air than a turbo.

supercharger with intercooler. now we're talking. As seen on some big engines.

I enjoyed that. Two small points, though. First, the injection of oxygen alone would not "cause the engine to melt". There is no reason why it should. The reason why nitrous oxide is preferred to pure oxygen is because there is actually far more oxygen in a tank of (liquid) nitrous oxide than there is in the same-sized tank of (compressed gas) oxygen. Second, a turbocharger does not itself heat the gas, inadvertently or otherwise. It just makes use of the hot gas already available at the exhaust.

I agree I should have said reduced pressure rather than vacuum or should have said part vacuum. Atmospheric pressure will fill any area whee the pressure is reduced - its will attempt to normalise and balance.

I had a 1963 Corvair Monza Spyder that had a Turbo charged air-cooled pancake 6 cylinder engine. It had a manifold vacuum/pressure gauge on the dash. As you put the pedal to the metal you could watch the vacuum drop from about 8" down to 0 and then the turbo Charger kicked in and you literally would slide back in the seat as it did. The gauge would then be climbing into the psi side as the compressor pushed the air in. Back then we wrapped the cross over pipe with asbestos wrap soaked in "water glass" or sodium silicate as we now know it.That was done to keep the exhaust gases hotter and add roughly 5 to 8 HP to your engine. At the lower RPM your manifold vacuum was created by the piston drawing in the air, the positive pressure was created by the turbo charger. The vacuum decreased in the manifold since the required air needed by the pistons in essence was being throttled back by the opening areas of the manifold, the roughness of the surfaces (which is why people would polish the interior surfaces and the ports) and the area of the carburetor throat. The positive pressure generated by the turbo charger overcame those restrictions. The higher the RPM's the less able for the normally aspirated engine was able to draw the required volume and therefore the vacuum would decrease and when it got to zero you were literally oxygen deprived or at least your engine was.

<Ascends soapbox>

This thread is a great example of a little knowledge being a dangerous thing, and everyone have an opinion that contains a grain of truth, including me.

A turbocharger compresses the air and fuel entering an internal combustion engine's cylinders. Period.

< Exit, stage left>

Simplistic comment but 100% accurate. The effects of compressing the intake charge are many but not complex or beyond comprehension to the practical mind.

Guess what? I was hiding behind the curtain on stage left. Now that i have 'collared' you, can you give us a formula that provides an answer for how much the temperature of the compressed gas rises in Deg K / KPa?

Jim

From the gas laws:

Pressure1 x Volume1 x Temperature1 = Pressure2 x Volume2 x Temperature2

where temperatures are in kelvins (I believe the expression degrees Kelvin is out of fashion).

don't do formulas ugh!

Its about -20deg C ish when it comes out of the intercooler though.