Ninehigh
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| posted on 5/2/13 at 09:33 PM |
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Turbo vs supercharger in modern engines
Just a thought, given that 99% of modern diesels and an increasing number of petrol engines have a turbo, could there be a benefit to a manufacturer
supercharging instead?
I'm figuring that "off boost" periods (steady speed) wouldn't really exist with a supercharger, but that would be counteracted
with needing less throttle to begin with. With the advantage of no turbo lag surely supercharging is the way to go, or am I missing something?
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matt_gsxr
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| posted on 5/2/13 at 09:37 PM |
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If there were a benefit, then why are they not all doing it?
I think the argument against supercharging are all to do with fuel economy.
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wylliezx9r
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| posted on 5/2/13 at 09:39 PM |
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Modern turbos are more efficient than superchargers, its as simple as that.
I spent a lot of money on booze, birds and fast cars. The rest I just squandered.
George Best
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liam.mccaffrey
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| posted on 5/2/13 at 10:00 PM |
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I would think that more turbos are used because most normal driving is done below the boost threshold for economy, with the higher revs and power
available when needed. Best of both worlds in a petrol engine.
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bi22le
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| posted on 5/2/13 at 10:08 PM |
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Possibly cheaper aswell?
Remeber the BMini was SC and then changed to turbo. They must of done it for a reason.
Not a highjack but maybe a little bit of fun \ game.
What BRAND NEW PRODUCTION cars still offer a supercharged model?
Jaguar - Various
Mercedes - Various
Audi \ Seat - A1, leon and others are twin charged
Any other?
Track days ARE the best thing since sliced bread, until I get a supercharger that is!
Please read my ring story:
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Me doing a sub 56sec lap around Brands Indy. I need a geo set up! http://www.youtube.com/watch?v=EHksfvIGB3I
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PSpirine
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| posted on 5/2/13 at 10:50 PM |
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Yes we do!
RANGE ROVER - renowned for fuel economy, I think you'll find.
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Ninehigh
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| posted on 5/2/13 at 11:25 PM |
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quote:
Originally posted by liam.mccaffrey
I would think that more turbos are used because most normal driving is done below the boost threshold for economy, with the higher revs and power
available when needed. Best of both worlds in a petrol engine.
That's why I said about needing less throttle, surely the ecu would only be delivering enough power to satisfy how far your foot is pressed.
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hobbsy
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| posted on 6/2/13 at 12:16 AM |
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I think one of the main differences is that the energy required to spin a turbo is effectively "free" from exhaust gases whilst a
supercharger is more of a parasitic load on the engine as it's crank driven like an alternator.
I think a turbo charger is always going to be more fuel efficient although a supercharge may give a better power delivery and response. But the gap
is narrowing with variable geometry turbo chargers etc.
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coyoteboy
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| posted on 6/2/13 at 12:26 AM |
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Using an engine with the throttle more closed makes it less efficient thermodynamically. There is a lower limit on the fuel air ratio, meaning you
can't run super leanunlike a diesel.
Fundamental differences I'm the two engine techs mean what works on one doesn't on the other.
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NigeEss
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| posted on 6/2/13 at 12:44 AM |
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There is one big thing in a superchargers favour.....................
They sound ace
Time is an illusion. Lunchtime doubly so.................Douglas Adams.
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Slimy38
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| posted on 6/2/13 at 08:15 AM |
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I seem to remember someone mentioning that turbo's are easy to get through type approval emissions tests while maintaining decent numbers. With
the emissions tests based on low revs (just above idle) they leave the turbo 'inactive' to make sure there are minimal emissions. Then
when the turbo spins up later in the revs they get the BHP numbers that sell the cars. It's a salesman's wet dream, and in a market based
on profit it's money that rules.
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hughpinder
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| posted on 6/2/13 at 08:31 AM |
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You could probably have an ECU controlled magnetic clutch so the supercharger doesnt take any load below (say) 5% to get good emissions, or even one
where the magnetic resistance increases with throttle position so the supercharger doesnt fully engage until you get to (say) 30%+ of WOT, but then
that adds even more cost! I guess you wouldn't for our sort of car as the complexity would outweigh the fuel gains.
Hugh
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MikeRJ
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| posted on 6/2/13 at 09:46 AM |
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quote:
Originally posted by Ninehigh
Just a thought, given that 99% of modern diesels and an increasing number of petrol engines have a turbo, could there be a benefit to a manufacturer
supercharging instead?
I'm figuring that "off boost" periods (steady speed) wouldn't really exist with a supercharger, but that would be counteracted
with needing less throttle to begin with. With the advantage of no turbo lag surely supercharging is the way to go, or am I missing something?
"Less" throttle is a bad thing. It increases pumping losses and reduces thermal efficiency through lower dynamic CR. The whole point of
small displacement engines with turbochargers is than under cruise conditions the throttle is opened more than it would be on a larger engine, making
it run more efficiently.
A supercharger has much higher parasitic and operating losses than a turbo, it's noisier, larger, more expensive to make and requires a
mechanical drive system that reduces the options for mounting it to the engine.
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phelpsa
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| posted on 6/2/13 at 07:43 PM |
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The main advantage is that a turbo recovers a certain amount of heat energy from the exhaust that otherwise would be wasted. This means that the
parasitic loss for a given amount of useful work output is less, and efficiency is therefore greater.
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JC
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| posted on 6/2/13 at 08:57 PM |
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Aren't the VW TFSI engines turbo and supercharged?
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PSpirine
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| posted on 6/2/13 at 09:31 PM |
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quote:
Originally posted by JC
Aren't the VW TFSI engines turbo and supercharged?
Yes but VAG aren't known for the simplicity of their systems.
That's what £65bn of engineering spend budget gets you.
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phelpsa
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| posted on 6/2/13 at 09:38 PM |
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quote:
Originally posted by JC
Aren't the VW TFSI engines turbo and supercharged?
IIRC it's a tiny supercharger that is clutched out as soon as the turbo is spooled.
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Slimy38
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| posted on 6/2/13 at 09:42 PM |
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quote:
Originally posted by PSpirine
quote:
Originally posted by JC
Aren't the VW TFSI engines turbo and supercharged?
Yes but VAG aren't known for the simplicity of their systems.
That's what £65bn of engineering spend budget gets you.
Even the VW cars have now dropped the supercharger and do turbo only... although as you say that may be because they were massively complicated.
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