Twin Turbos

[developer]

Wills2 said:

Why would you want that unless you're ploughing a field or towing the space shuttle?

My 800ft/lbs has makes 3rd gear feel like 2nd gear, and whilst traction is a problem, it's a hoot on a decent road, with overtaking power that I haven't felt since my superbike days.

Such fun.

[Loyly]

McVities said:

Do they run those large torque figures from idle rpm too?

Thankfully not, that's why they're exciting!

[nottyash]

gweaver said:

HoHoHo said:

the Tri turbo BMW Diesel engine is a work of art

That may be the case, but it's also nightmarish in it's complexity. I wouldn't want to own one out of warranty. It'll be interesting to see if multiple knackered turbos put these beyond economical repair, or if the used values hold up enough.

Did you say the same thing 25 years ago about electric windows and central locking

[Willy Nilly]

Thanks all.

I asked on another channel about these : http://www.challenger-ag.com/EMEA/GB/products/trac... with the 16.8l V12 with 4 turbos, and it seems that one turbo feeds another one on each cylinder bank. A bi-compound set up

Edited by Willy Nilly on Sunday 4th December 20:57

[AlexS]

gweaver said:

Jim AK said:

f1nn said:

It's an attempt to combine the advantages of both supercharging and turbocharging, getting around 170bhp from a 1.4.

I was just muddying the waters!

Mate doesn't rate them too highly, thinks the internals are probably a meltdown looking for somewhere to happen.

The idea is that the supercharger provides the low rpm response, whilst the turbocharger takes over in the mid range (>2500rpm IIRC). Interesting idea, but unfortunately engineered by VW - those engines have a terrible reputation for reliability and I think they were quietly dropped in favour of a 1.4 turbo without the supercharger. Some of the recent VW 1.4 petrols are also known for piston slap.

One development that I'm a bit surprised not to have seen is the use of an exhaust turbine and generator to charge the battery in a hybrid. I'd have thought it a good source of a little (almost) "free" power, with the benefits of not needing an intercooler, or reduced compression ratio, and of potentially excellent throttle response from the electric side of the hybrid system.

That's how the Porsche 919 operates in the WEC. One large turbo for the engine, and a 2nd free power turbine driving a generator.

[gweaver]

AlexS said:

That's how the Porsche 919 operates in the WEC. One large turbo for the engine, and a 2nd free power turbine driving a generator.

Thanks, I didn't know that, and couldn't find much information online about it. I've just discovered that the MGU-H in a Formula one engine is a turbine driving a generator shaft. So it has been done, but I think yet to make it into a road car.

[AlexS]

gweaver said:

Thanks, I didn't know that, and couldn't find much information online about it. I've just discovered that the MGU-H in a Formula one engine is a turbine driving a generator shaft. So it has been done, but I think yet to make it into a road car.

The MGU-H in F1 is slightly different to the Porsche in that it is a complete turbo unit combined with the generator. This has the advantage that the motor can be used to spool the turbo up, if required, reducing its response time but can only generate electrical power if the compressor has reached its boost target and the wastegate needs to open to control the speed.

[gweaver]

AlexS said:

The MGU-H in F1 is slightly different to the Porsche in that it is a complete turbo unit combined with the generator.

Thanks for the info.

[AW111]

gweaver said:

Thanks, I didn't know that, and couldn't find much information online about it. I've just discovered that the MGU-H in a Formula one engine is a turbine driving a generator shaft. So it has been done, but I think yet to make it into a road car.

For another variation, we had a Detroit Diesel truck engine at work a few years back which had mechanical energy recovery - the (single) turbo had a gear drive to the crank (via a fluid coupling iirc), which apparently provided 10% of the total power at peak load.

[kambites]

popeyewhite said:

Off the line maybe, but actually modified M5s and E63s run to 100 in 7.5, which is quicker than the Tesla.

Than a P90, perhaps. The P100D does 0-100 in 6.5 seconds.

[Vitorio]

AW111 said:

For another variation, we had a Detroit Diesel truck engine at work a few years back which had mechanical energy recovery - the (single) turbo had a gear drive to the crank (via a fluid coupling iirc), which apparently provided 10% of the total power at peak load.

Isnt that "just" a normal rotrex like supercharger? Nothing turbo or energy recovery about it

[AW111]

Vitorio said:

AW111 said:

For another variation, we had a Detroit Diesel truck engine at work a few years back which had mechanical energy recovery - the (single) turbo had a gear drive to the crank (via a fluid coupling iirc), which apparently provided 10% of the total power at peak load.

Isnt that "just" a normal rotrex like supercharger? Nothing turbo or energy recovery about it

No, it's primarily an exhaust-driven turbocharger. At full boost, it extracts more energy from the exhaust than is needed for compressing the inlet charge, so feeds some to the crank via a gear reduction.

It's an idea that dates back to the 50's (or earlier), but it's the only production engine I have seen that uses it.

[Vitorio]

AW111 said:

No, it's primarily an exhaust-driven turbocharger. At full boost, it extracts more energy from the exhaust than is needed for compressing the inlet charge, so feeds some to the crank via a gear reduction.

It's an idea that dates back to the 50's (or earlier), but it's the only production engine I have seen that uses it.

Ahh right, i got your first post a bit backwards, cool system!

[SuperchargedVR6]

gweaver said:

Jim AK said:

f1nn said:

It's an attempt to combine the advantages of both supercharging and turbocharging, getting around 170bhp from a 1.4.

I was just muddying the waters!

Mate doesn't rate them too highly, thinks the internals are probably a meltdown looking for somewhere to happen.

One development that I'm a bit surprised not to have seen is the use of an exhaust turbine and generator to charge the battery in a hybrid. I'd have thought it a good source of a little (almost) "free" power, with the benefits of not needing an intercooler, or reduced compression ratio, and of potentially excellent throttle response from the electric side of the hybrid system.

Nice idea but it would have to be a combined turbo/alternator system, otherwise squeezing exhaust gases through a tiny orifice without a compressor on the other end as compensation, would be the mother of all exhaust restrictions. And cars already have separate alternators to charge the batteries.

[toon10]

rayyan171 said:

Twin scroll turbocharges, again used by BMW, use one turbocharger only. The turbo exhaust gas flow port is split into two. The turbo equally pushes gases coming from cylinders 1, 2 and 3 and then from 4, 5, and 6 into the compressor. This in turn creates a parallel twin turbo effect. Normally with a single conventional turbo, the gases pressure decreases a bit as they collide with the other gases coming from the other cylinders, reducing the overall pressure. The twin scroll significantly decreases this decrease in pressure from the gases, and higher pressure results in better boost, better efficiency etc. which is why BMW use this now instead of conventional parallel twin turbos.

Lots of manufacturers have their needs, so it was much harder to apply them to NA cars, therefore turbos are very commonly used to meet the needs.

Hopefully this solves many questions, correct me if I am wrong.

Interesting insight. I have the twin scroll on my car and wasn't aware of the engineering behind the idea. I know BMW changed from the twin turbo setup to the single twin scroll one on my car but are there any other manufacturers using this setup and if not why? Seems to be a cheaper and better alternative to adding 2 turbos?

[gweaver]

SuperchargedVR6 said:

Nice idea but it would have to be a combined turbo/alternator system, otherwise squeezing exhaust gases through a tiny orifice without a compressor on the other end as compensation, would be the mother of all exhaust restrictions. And cars already have separate alternators to charge the batteries.

I'm sure the electronics wouldn't be trivial, but possibly not much different to the challenges of dealing with regenerative braking. Super capacitors and an electrically driven compressor perhaps? Both are in development.
In a proper hybrid it'd make more sense to use the electical energy to drive the wheels than a compressor.

There's a myriad of different ways to combine stuff, but IMHO the ideal solution would recover energy from the exhaust system and make it available when needed. A turbo-supercharger doesn't do a great job of this because it can't store the energy (other than a bit of kinetic energy in the turbine). The right compromise for a road car would, you would hope, be simpler than the solutions in F1, but still deliver some of the efficiency gains.

[mackie1]

toon10 said:

Interesting insight. I have the twin scroll on my car and wasn't aware of the engineering behind the idea. I know BMW changed from the twin turbo setup to the single twin scroll one on my car but are there any other manufacturers using this setup and if not why? Seems to be a cheaper and better alternative to adding 2 turbos?

The new turbo V6 in the Audi S4 and S5 uses a single twin scroll turbo in the V. Pretty neat setup with a very short path from the cylinders to the turbo inlets.

[Otispunkmeyer]

aka_kerrly said:

Just to confuse things even more you also have cars like a Toyota MR2 which has a twin entry turbo which people often think means there are 2 turbos!!

Those really should be twin scroll... That's the volute or snail looking housing.

I think modern machining is able to produce better, more complex turbine and compressor wheels so they work over a great range of flow rates.

Add to that, variable inlet vane control and you make those wheels work over a further increased range. You want small, light wheels so that they spin up when you put your fit down. I think increasingly we'll see electric compressors which can spin to 70krpms in milliseconds, providing you instant response.

(Until everyone drives an EV of course)

[HoHoHo]

Otispunkmeyer said:

aka_kerrly said:

Just to confuse things even more you also have cars like a Toyota MR2 which has a twin entry turbo which people often think means there are 2 turbos!!

Those really should be twin scroll... That's the volute or snail looking housing.

I think modern machining is able to produce better, more complex turbine and compressor wheels so they work over a great range of flow rates.

Add to that, variable inlet vane control and you make those wheels work over a further increased range. You want small, light wheels so that they spin up when you put your fit down. I think increasingly we'll see electric compressors which can spin to 70krpms in milliseconds, providing you instant response.

(Until everyone drives an EV of course)

Or the 61 plate 335i I had which had a big badge on to of the engine.................

TWIN TURBO POWER

WTF does that mean.........it means BMW went from two to one turbo from the previous to that engine but didn't want to upset the punters

[Otispunkmeyer]

AlexS said:

gweaver said:

Jim AK said:

f1nn said:

It's an attempt to combine the advantages of both supercharging and turbocharging, getting around 170bhp from a 1.4.

I was just muddying the waters!

Mate doesn't rate them too highly, thinks the internals are probably a meltdown looking for somewhere to happen.

The idea is that the supercharger provides the low rpm response, whilst the turbocharger takes over in the mid range (>2500rpm IIRC). Interesting idea, but unfortunately engineered by VW - those engines have a terrible reputation for reliability and I think they were quietly dropped in favour of a 1.4 turbo without the supercharger. Some of the recent VW 1.4 petrols are also known for piston slap.

One development that I'm a bit surprised not to have seen is the use of an exhaust turbine and generator to charge the battery in a hybrid. I'd have thought it a good source of a little (almost) "free" power, with the benefits of not needing an intercooler, or reduced compression ratio, and of potentially excellent throttle response from the electric side of the hybrid system.

That's how the Porsche 919 operates in the WEC. One large turbo for the engine, and a 2nd free power turbine driving a generator.

In a passenger car back pressure constraints probably stop that. Especially diesel where you've got myriad filters and other kit in the flow already. Back pressure can hurt emissions and it definitely hurts fuel efficiency. The back pressure limits are quite tight too, I think on the big Volvo engines we worked on it was 18 kPa and 12 of that was taken up by the SCR!

In racing they have also used long 4-2-1 manifolds for a long time (obviously depends on cylinder count) as it keeps in cylinder charge cooler and therefore combustion is less likely to knock. This allows higher compression ratios, which is useful. In a normal car the need to heat up the catalysts pronto means they don't use them and therefore are more constrained on pushing the compression.

Except Mazda, who do use them as part of their sky active technology package. Their two litre petrol is 14:1! They of course have other enabling tech to reach this but 14:1 would typically have a petrol engine into a very inefficient window because of how badly you need to retard the timing to stop knock.