Turbo & Super chargers
Thread Starter
Join Date: Feb 2002
Location: Dublin
Posts: 2,547
Likes: 0
Received 0 Likes
on
0 Posts
Turbo & Super chargers
What's the difference between turbo and super chargers?
I believe I understand the basics of a turbo charger. It uses the pressure in the exhaust fumes to turn a turbine, which in turn compresses the air before it enters the cylindars. Therefore there is more air in the cylinders, so you can add more fuel. More air and fuel = more power. I think I'm ok on that?
What what exactly is a supercharger? And if the answer doesn't give it away, then which one is better?
Thanks guys if you can answer that one! It's bugged me for ages!
dp
I believe I understand the basics of a turbo charger. It uses the pressure in the exhaust fumes to turn a turbine, which in turn compresses the air before it enters the cylindars. Therefore there is more air in the cylinders, so you can add more fuel. More air and fuel = more power. I think I'm ok on that?
What what exactly is a supercharger? And if the answer doesn't give it away, then which one is better?
Thanks guys if you can answer that one! It's bugged me for ages!
dp
Join Date: Mar 2000
Location: TL487591
Posts: 1,639
Likes: 0
Received 0 Likes
on
0 Posts
A supercharger is a generic term for a device which pressurises the air used by the engine for combustion.
A turbocharger is a specific type of supercharger which employs a turbine driven by the exhaust of the self same engine, to do the pressurisation.
2D
A turbocharger is a specific type of supercharger which employs a turbine driven by the exhaust of the self same engine, to do the pressurisation.
2D
Join Date: Oct 1999
Location: UK
Posts: 3,325
Likes: 0
Received 0 Likes
on
0 Posts
2Donks is right - the full name for a turbo charger is a turbo super charger.
However, in common usage a supercharger is taken to mean a mechanically-driven compressor (driven off the engine) which compresses the intake air.
Turbochargers are well suited to engines that run a fairly constant speeds - like aero engines. They are not good for car engines because of 'turbo lag' - the throttle is suddenly opened, but the 'boost' doesn't increase untill the exhaust gas pressure increases, spins the turbine faster, which in turn spins the compressor faster, to give the required 'boost' - a tad later than the engine needs it. This can be obviated to some extent by running the compressor at a higher boost than the engine needs, and venting the excees boost through a waste gate. On opening the throttle, the waste gate can close to provide near-instant boost.
The supercharger, being mechanically coupled to the engine, will be spun faster as the engine speeds up and its output boost will always be matched to the engine RPM. More expensive cars tend to have supercahrgers rather than turbochargers.
Some big radial aero engines used turbo-compound technology. The exhaust gasses drove turbines which were geared to the engine crankshaft, so their power was supplementing that of the engine.
SSD
However, in common usage a supercharger is taken to mean a mechanically-driven compressor (driven off the engine) which compresses the intake air.
Turbochargers are well suited to engines that run a fairly constant speeds - like aero engines. They are not good for car engines because of 'turbo lag' - the throttle is suddenly opened, but the 'boost' doesn't increase untill the exhaust gas pressure increases, spins the turbine faster, which in turn spins the compressor faster, to give the required 'boost' - a tad later than the engine needs it. This can be obviated to some extent by running the compressor at a higher boost than the engine needs, and venting the excees boost through a waste gate. On opening the throttle, the waste gate can close to provide near-instant boost.
The supercharger, being mechanically coupled to the engine, will be spun faster as the engine speeds up and its output boost will always be matched to the engine RPM. More expensive cars tend to have supercahrgers rather than turbochargers.
Some big radial aero engines used turbo-compound technology. The exhaust gasses drove turbines which were geared to the engine crankshaft, so their power was supplementing that of the engine.
SSD
Join Date: Aug 2001
Location: UK
Posts: 2,410
Likes: 0
Received 0 Likes
on
0 Posts
2Ds
Happy to bow to your greater knowledge but thought that the difference was that a supercharger is mechanically driven by the engine and the turbocharger is (as you say) driven by the exhaust gases.
FD
Darn SSD; you got in their with the agility of a Chippy!
Happy to bow to your greater knowledge but thought that the difference was that a supercharger is mechanically driven by the engine and the turbocharger is (as you say) driven by the exhaust gases.
FD
Darn SSD; you got in their with the agility of a Chippy!
Why do it if it's not fun?
Join Date: Jul 2001
Location: Bournemouth
Posts: 4,779
Likes: 0
Received 0 Likes
on
0 Posts
The terminology caused endless confusion on my ATPL course.
The word "Supercharger" is a generic term for a device which boosts the manifold pressure.
There are two types of supercharger. There's an engine-driven supercharger, also known (and here's where the confusion comes in) as a "Supercharger". And there's an exhaust-driven type, known as a "Turbocharger". Some careful reading of questions was required whenever you saw the word "supercharger".
In practice, though, I agree with SSD - if you hear the word "supercharger" outside of a CAA exam it almost certainly refers to an engine-driven boost pump.
FFF
-----------
The word "Supercharger" is a generic term for a device which boosts the manifold pressure.
There are two types of supercharger. There's an engine-driven supercharger, also known (and here's where the confusion comes in) as a "Supercharger". And there's an exhaust-driven type, known as a "Turbocharger". Some careful reading of questions was required whenever you saw the word "supercharger".
In practice, though, I agree with SSD - if you hear the word "supercharger" outside of a CAA exam it almost certainly refers to an engine-driven boost pump.
FFF
-----------
Official PPRuNe Chaplain
Join Date: Apr 2001
Location: Witnesham, Suffolk
Age: 80
Posts: 3,498
Likes: 0
Received 0 Likes
on
0 Posts
Nope, FFF and 2D are different folks. Or were, last time I met them.
The standard definition in the auto industry (where I spent my "working" life) is that supercharger is engine-driven (for example, off camshaft or crankshaft), and turbocharger is exhaust driven.
I think someone once used an electrically-powered supercharger, but can't remember who ... might have been Alfa Romeo.
A turbocharger is more efficient in use of power than is a supercharger - but has the drawback of "lag" etc as mentioned by SSD. There are many and wondrous schemes to overcome that - "low-blow" turbo, multi-stage turbo, and stuff I'm probably still not supposed to talk about.
But I'm glad to see the CAA uses different definitions anyway.
The standard definition in the auto industry (where I spent my "working" life) is that supercharger is engine-driven (for example, off camshaft or crankshaft), and turbocharger is exhaust driven.
I think someone once used an electrically-powered supercharger, but can't remember who ... might have been Alfa Romeo.
A turbocharger is more efficient in use of power than is a supercharger - but has the drawback of "lag" etc as mentioned by SSD. There are many and wondrous schemes to overcome that - "low-blow" turbo, multi-stage turbo, and stuff I'm probably still not supposed to talk about.
But I'm glad to see the CAA uses different definitions anyway.
Join Date: Mar 2000
Location: TL487591
Posts: 1,639
Likes: 0
Received 0 Likes
on
0 Posts
Thanks Keef
Yes, whilst I have once been in the same hangar as FFF, we are definitely not the same person.
I am flattered that FFF posted the same information as me though, even using some of the same words in the same order
Fools seldom differ !!
2Donkeys
Yes, whilst I have once been in the same hangar as FFF, we are definitely not the same person.
I am flattered that FFF posted the same information as me though, even using some of the same words in the same order
Fools seldom differ !!
2Donkeys
Join Date: Mar 2002
Location: back at the grind stone
Posts: 199
Likes: 0
Received 0 Likes
on
0 Posts
So whats the difference between turbo 'charging' and turbo 'normalising' ??
Am I right in thinking 'charging' gives you boost power, while 'normaslising' somehow gives you sea level density perf. ???
Am I right in thinking 'charging' gives you boost power, while 'normaslising' somehow gives you sea level density perf. ???
Join Date: Mar 2000
Location: TL487591
Posts: 1,639
Likes: 0
Received 0 Likes
on
0 Posts
Oscar Duece.
Correct. Turbocharging will tend to give additional pressure up to and often over 40 inches on a typical piston engine.
Turbonormalising is intended to deliver sea-level like pressures (say 30ish inches) as the aircraft climbs. The advantages to Turbonormalising are in terms of consistent fuel-burn and engine wear and tear.
2D
Correct. Turbocharging will tend to give additional pressure up to and often over 40 inches on a typical piston engine.
Turbonormalising is intended to deliver sea-level like pressures (say 30ish inches) as the aircraft climbs. The advantages to Turbonormalising are in terms of consistent fuel-burn and engine wear and tear.
2D
Supercharged PPRuNer
Join Date: Nov 2000
Location: Doon the watter, a million miles from the sandpit.
Posts: 1,183
Received 0 Likes
on
0 Posts
Did someone call?
SSD’s description of the pros & cons is pretty much spot on. A few more observations:
Advantages of mechanically driven superchargers include:
(1) They run much cooler than turbo-superchargers (as there is no exhaust gas to contend with) which helps to keep engine-bay temperatures down.
(2) As SSD explains, ‘lag’ (the delay between opening the throttle and the engine delivering the goods) is pretty much non-existent, making the engine behave like a much larger normally aspirated one, rather than a smaller boosted machine. This isn't particularly relevant in an aircraft engine, but can make a big difference in automotive applications. VW reckoned their G60 supercharger produced 80% of available boost within 0.4 seconds of opening the throttle, effectively multiplying the cubic capacity by 1.6, and giving 50% more torque increase than an equivalent turbo.
(3) Lower exhaust back-pressure than with a turbo, (as there is no turbine to restrict gas flow) which can improve scavenging of the cylinders and increase exhaust gas velocity. This is probably of more importance in aircraft applications, and one reason why RR didn’t turbocharge the Merlin, going instead for bigger and better superchargers. The high velocity exhaust gas gave positive thrust, which would have been reduced if fed through a turbo.
(4) The howl from a supercharger makes your engine sound like its possessed by Satan himself.
Disadvantages:
(1) They are less efficient than a turbo, as they use engine power to spin them. By comparison, a turbo – driven by exhaust gas – simply converts energy that would otherwise be lost down the exhaust pipe (unless you’ve got a Merlin).
(2) They are mechanically more complex, generally resulting in greater initial cost and more frequent servicing.
(3) If a supercharger decides to lunch itself, it has a nasty habit of spewing bits of compressor into the inlet manifold, straight towards the reciprocating bits of your engine . . .
(4) Lower adiabatic efficiency than a turbo, resulting in greater heating of the intake air, and making charge air cooling (intercooling) more critical. (I’m not sure why this is the case, but I read it in a book with lots of big equations, so it must be true).
It’s difficult to say whether one is better than the other – it really depends on the application and the quality of the design and installation. They’ve both had so much development over the years that there is very little to choose between them.
SSD’s description of the pros & cons is pretty much spot on. A few more observations:
Advantages of mechanically driven superchargers include:
(1) They run much cooler than turbo-superchargers (as there is no exhaust gas to contend with) which helps to keep engine-bay temperatures down.
(2) As SSD explains, ‘lag’ (the delay between opening the throttle and the engine delivering the goods) is pretty much non-existent, making the engine behave like a much larger normally aspirated one, rather than a smaller boosted machine. This isn't particularly relevant in an aircraft engine, but can make a big difference in automotive applications. VW reckoned their G60 supercharger produced 80% of available boost within 0.4 seconds of opening the throttle, effectively multiplying the cubic capacity by 1.6, and giving 50% more torque increase than an equivalent turbo.
(3) Lower exhaust back-pressure than with a turbo, (as there is no turbine to restrict gas flow) which can improve scavenging of the cylinders and increase exhaust gas velocity. This is probably of more importance in aircraft applications, and one reason why RR didn’t turbocharge the Merlin, going instead for bigger and better superchargers. The high velocity exhaust gas gave positive thrust, which would have been reduced if fed through a turbo.
(4) The howl from a supercharger makes your engine sound like its possessed by Satan himself.
Disadvantages:
(1) They are less efficient than a turbo, as they use engine power to spin them. By comparison, a turbo – driven by exhaust gas – simply converts energy that would otherwise be lost down the exhaust pipe (unless you’ve got a Merlin).
(2) They are mechanically more complex, generally resulting in greater initial cost and more frequent servicing.
(3) If a supercharger decides to lunch itself, it has a nasty habit of spewing bits of compressor into the inlet manifold, straight towards the reciprocating bits of your engine . . .
(4) Lower adiabatic efficiency than a turbo, resulting in greater heating of the intake air, and making charge air cooling (intercooling) more critical. (I’m not sure why this is the case, but I read it in a book with lots of big equations, so it must be true).
It’s difficult to say whether one is better than the other – it really depends on the application and the quality of the design and installation. They’ve both had so much development over the years that there is very little to choose between them.
Join Date: Sep 2000
Location: A small corner of the Belgian Empire
Posts: 89
Likes: 0
Received 0 Likes
on
0 Posts
The Wright Turbo Compound referred to by SSD was a very clever piece of engineering, if a little temperamental. Curtiss Wright always referred to the clever bits as "power recovery turbines".
CW experimented initially with 6 PRTs per engine, but eventually settled for three, each harnessing the exhausts from 6 cylinders, which saved 200 lbs with no loss of power. Each only a foot in diameter, the PRTs were arranged radially behind the cylinders, and drove quill shafts geared through fluid clutches to the crankshaft. Running at a constant 19,000 rpm, they added about 400 bhp for nowt. They also took a lot of the bark out of the exhaust noise.
Had this device not been developed, the DC-7C and Starliner would have had to be the first post-war 6 engined airliners. The Wright Turbo-Compound was in production for 8 years and at the height of its era, some 11,000 were in service.
CW experimented initially with 6 PRTs per engine, but eventually settled for three, each harnessing the exhausts from 6 cylinders, which saved 200 lbs with no loss of power. Each only a foot in diameter, the PRTs were arranged radially behind the cylinders, and drove quill shafts geared through fluid clutches to the crankshaft. Running at a constant 19,000 rpm, they added about 400 bhp for nowt. They also took a lot of the bark out of the exhaust noise.
Had this device not been developed, the DC-7C and Starliner would have had to be the first post-war 6 engined airliners. The Wright Turbo-Compound was in production for 8 years and at the height of its era, some 11,000 were in service.
