Twin (Compound) Charging - Anyone?

[BLSTIC]

Wouldn't it make more sense to have the main restriction in the exhaust (the smaller turbine) before the larger turbine, and have a large wastegate for it? That said there could be other issues like using existing parts, or engine bay room limitations.

cya
Ben

[Polyal]

Interestig thread. Im 99.9% sure VW offer a turbo/blower setup in there golf in Europe (maybe even here, remember reading it in a Wheels/Motor mag).

It would be insane, instant boost of a charger with the top end being a turbo, with a 4L!!! VW uses a 1.4 or similar I think, ill have a look; effectively turns it into a 3L or so but obviously uses minimal space.

Whether or not its worth it is a useless arguement, its just money, and if you have it then give it a crack I say.

Also remember a thread on this site about a WRX in the US having the twin charger setup.

[Polyal]

Heres a link for the golf after a quick google

http://www.vwvortex.com/artman/publi...ter_1496.shtml

About half way down...

Originally Posted by VW Site

Wolfsburg, 29 August 2005 - At the International Motor Show (Cars) in Frankfurt, Volkswagen is presenting to the general public a ground-breaking innovation in the drive sector: The world’s first twin-turbocharged FSI engine – the “Twincharger”. The compact 1.4 litre direct-injection engine develops up to 125 kW / 170 PS and has a maximum torque of 240 newton metres in the range from 1750 to 4500 rpm thanks to the combination of an exhaust turbocharger with a mechanically driven compressor.

The 1.4 litre engine delivers a power output of 90 kW / 121 PS per litre, representing a peak value for a series production four-cylinder engine. Furthermore, the “Twincharger” delivers a torque corresponding to a naturally aspirated engine with a swept volume of approx. 2.3 litres. And its fuel consumption is around 20 percent lower.

Another performance variant of this innovative TSI engine with 103 kW / 140 PS (maximum torque 220 newton metres) will be available from early 2006, initially in the Touran compact MPV, and after that the Golf will also be available with this engine.

[BLSTIC]

I see no reason why it wouldnt work. Exept the really low compression ratio that would be needed to run at high boost.

But given that my Mk1 Zephyr has a compression ratio of 6.8:1 out of the box and (other examples) run smooth as, lower is possible. Hell, once upon a time engines were cranked by hand, so compression ratio's were lower still at one time.

The Lancia Delta Intergralé was another car with this setup. A blower making ~10psi, which was disconnected (for some reason, probably heat) when the turbo kicked in at whatever the rally cars ran...

[Rollin]

I think it's a great idea, but what is better, or what will even work, would depend on the desired outcome.

For Instance:

I want bulk hp from idle to redline. To get bulk torque from idle, I would either need a really small turbo that spools early (and would have SFA max airflow capability) or a roots type supercharger.

To get bulk hp at the other end of the rev range, Running a roots that could supply lots of boost up to redline would mean using a big mofo, which would have lots of mechanical drag and be nowhere near as efficient as a turbo at big power outputs.

So running a big turbo is better for big hp, but then you have lots of lag to deal with, killing objective number one.

So, if you got a smallish roots blower that could give you good boost from idle to about 2500-3000rpm, and a big turbo that would in a conventional setup start to spool hard at 3000-3500rpm, you would have the best of both worlds...

The blower would be making boost as soon as you mash the throttle, and because you are getting boost from idle, you would have much more exhaust gas available to spool the turbo.

So the turbo starts to spool earlier (hopefully about the same time as the roots starts becoming inefficient) and it either:

Starts ramming the air into the supercharger (which will just compress it and push it into the motor)

Or:

Will suck air through a bypass between the blower and turbo, if you have the blower before the turbo

In the first case, I believe they 'share' the load, so neither has to work as hard as they otherwise would at the same power output, or in the second case, the blower would help the turbo out a little, but otherwise just sit there spinning until it was needed again.

Instant boost, instant hp, and as much as you want because you can just adjust the wastegate to get whatever boost level you want in the manifold

***

[Rollin]

[IMG]hxxp://i127.photobucket.com/albums/p148/Rollinfourlitre/twincharge.jpg[/IMG]

Dodgy paintshop pic FTW

In option B the blower blows through the turbo and then into the motor. As the turbo starts to boost, it will need to draw more air than the blower can supply, which would normally cause the blower to become a restriction, but then the bypass would open and the turbo could suck fresh air.

If you used a toyota blower, doing it that way would mean you could then disengage the clutch of the blower (since at that point it is redundant), reducing parasitic losses.

In Option A the blower would just compress the air from the turbo in the same way as it would compress fresh air.

Both of the above are more complex than a conventional turbo or blower setup, but the combination has all the strengths and few of the downsides of a turbo or blower setup.

[THORNSPAWN]

In a book I have, on turbocharging, it shows triple tandem turbo setups on tractor pull
diesels running up to 255psi boost at the manifold. each compressor adds to the
pressure from the the previous one ie. first turbo running 10psi, second turbo also set at
10psi, output from second turbo will be 20psi.

[fairmont1998]

4 turbos into 2 blowers seems to work ok for the Bandag Bullet....

[BLSTIC]

I never did think of the first method, with the bypass. Would be a good way to use a cheap, clutched blower on a large engine without overspeeding it. That way your SC14 (1G-GZE) supercharger could push 18psi (up to 3500rpm) while you are waiting for your T70 to spool.

cya
Ben

[Bipolar]

:

[Rollin]

4 turbos into 2 blowers seems to work ok for the Bandag Bullet....

You will probably find that the bandag bullet has a 2 stroke diesel in it, with only exhaust valves in the head.

When the injectors fires and the fuel burns, the piston is forced down, once it has gone down some way, the exhaust valve opens and starts letting the burnt gasses out of the chamber, the piston goes down further, uncovering the inlet port, fresh air is forced into the cylinder (and depending on cam size/timing) out the exhaust valve.

Forcing air out the exhaust valve on a diesel is not 'wasteful' as it is only air, no fuel, and it is good because it ensures that each cylinder is chock full of fresh air by the time the exhaust valve closes and the piston starts to rise, with no waste gasses from the last cycle to cost you power.

Those two stroke type diesels will not actually run without the supercharger, as they rely on the air being forced into the cylinder under pressure rather than the engine sucking it in by itself, because there is no actual "intake" stroke in this instance.

[outback_ute]

Virtually all jet engines are compound charging (compressor stages). As mentioned WRC Lancias in the early 80s had supercharging at low rpm and turbo at high rpm.

It could work, but geez it would be a tricky thing to set up, especially for a road car - it is actually simpler for a competition vehicle because you don't care so much about the part-throttle response. That also means it would cost a lot too.

[wilb]

It is true, the Bandag Bullet does have a two stroke in it. But it stills proves the point. Running a turbo into a supercharger works. The supercharger works off idle, instant power, but once the rpm comes up superchargers loose their grunt, but the turbo is there to help by then. You wouldn't, in my hunble opinon get more actual horsepower as such, but yu would get a much longer powerband. You would get the best of both worlds. No top end loss from the supercharger, no lag from the turbo. The Bandag Bullet runs two detroit V8 diesels in line, four turbos, two blowers, nitrous injection, its a 24 litre motor, 2200hp @ 3000rpm, 2800hp with nitrous :-)

[Aaron_EF8]

Diesel engines love hot intake air, they run on detonation basically, unlike petrol motors. The inlet temps of 4 turbochargers then 2 roots blowers would be insane.

[wilb]

Detonation is more common in petrols. Its an explosion of the fuel and air instead of controlled burning. Pinging if you like. Its when the fuel instead of getting ignited and burning a flame front across the top of the piston, just explodes in one hit. Diesels only compress air, once its compressed and the piston is near the top, then the fuel is injected. The diesel burns on its way in. And so long as the injector is pumping, it keeps burning. No explosion there. Only controlled burning.

[Aaron_EF8]

I know what detonation is.

Diesels run by compression ignition, which is a form of detonation in petrol engines, so pumping hot as hell air into a diesel is good, while it's bad for a petrol engine.

Comparing diesel engines and petrol engines doesn't work. They have pistons, rods, a crank, thats about where the similarities end.

Apart from the Group B Lancias, have there been any other production based cars that have used compound charging?

[BLSTIC]

The Nissan March Super Turbo did it, a turbo blowing through a supercharger. I think a couple of Audi's did it too...

[wilb]

Agreed, there are one or two differences between diesels and petrols. But those differences dont really matter in this debate. Ok, the hot air is a definate problem, but a turbo for sure, but would a supercharger really heat the air up that much? It would only be friction causing it to heat, not like the exhaust on the turbo. At any rate, everyone these days seems to have an air cooler somewhere. So there shouldnt really be a problem. And diesels dont run on 'basically detonation' :-)

[Aaron_EF8]

Roots superchargers (like on the Bandag Bullet) create intake air temps 100deg above ambient if setup properly, over 200deg higher if not sized/setup properly. A lot more than a properly sized turbo. Quite hard to intercool a roots blower too. Running methanol would negate most of this problem though.

Did you actually read Rollins post? 2 stroke diesels need air pumped into them to run, petrol engines don't, I'd say thats a fairly big difference.

Compression ignition being a form of detonation would mean diesels run by 'basically detonation'.

[wilb]

Far out on the blower/air temp, i didnt know that. I did read rollins post, and understood it. But. Detonation is an explosion. Diesels, two or four stroke ignite the fuel the same way, as you already know. But it superheats the air with high compression. Then, after the air is hot, then it pumps diesel in, which burns as its injected in. Obviously, you already know by burning it expands and forces the piston down. Im not trying to be smart, but thats controlled burning, not an explosion. The only way you could have detonation in a diesel is, a: the injection timing too far advanced, meaning the diesel has been squirted in before the cylinder is ready for it, it wouldnt burn, but explode. Or b: a leaking injector, where the fuel is not atomized correctly, if it doesnt burn complete it explodes. Its compression igniton, i would never contest you on that, just saying its ignition. It starts the fuel burning, it doesnt make it detonate.

[fairmont1998]

I have to agree with wilb.
Ignition = controlled flame front, be it diesel or petrol
Detonation = uncontrolled burning.

[fritzz]

here is a twin supercharged ls1 with good results. built here in wa

http://www.marksworkshop.com.au/Page...re/2xtreme.htm

[BLSTIC]

Aeron, fair enough with the temperature reference, but wouldnt a screw blower be a little more efficient than that (as they have internal compression, much like a centrifugal or vane supercharger)? I know rootes blowers are basically pump x litres of air from one side to another, but the screw type ones are true compressors. They also have the same boost characteristics as a rootes item, supposedly better efficiency, and a much higher price tag.

[Aaron_EF8]

The detonation/ignition thing, I believe we're talking about the same thing but with different words now.

The LS1 article is an intersting read, I would have thought it would be more difficult to set-up than what the story says. The Eaton blower is still a Roots design, although Eaton has refined the design quite a lot, and with the intercooler, temps are only about 20deg above ambient which is pretty good. With a turbo, it should build boost quicker than a centrifugal blower too.

Now someone do it to a 4.0! :P

[Rollin]

It would only be friction causing it to heat, not like the exhaust on the turbo.

This is where a lot of people get mixed up. Turbos do NOT heat the air due to the proximity of the exhaust and compressor housings!!

The air gets hot because it is compressed - I believe its linear too - double the pressure, double the temp, so 1L of air at 20* compressed down to 500mL should increase in temp to 40*. Not clear or the exact ratio, but I know more pressyre = more temp.

The pressure/temp correlation is why diesels run.

Fairmont1998 has the igntion/detonation definitions right.

[wilb]

Originally Posted by Rollin

This is where a lot of people get mixed up. Turbos do NOT heat the air due to the proximity of the exhaust and compressor housings!!

The air gets hot because it is compressed - I believe its linear too - double the pressure, double the temp, so 1L of air at 20* compressed down to 500mL should increase in temp to 40*. Not clear or the exact ratio, but I know more pressyre = more temp.

The pressure/temp correlation is why diesels run.

Fairmont1998 has the igntion/detonation definitions right.

That sounds like a fair call, makes perfect sense, i cant argue with that. My concern is still, there must be a heat difference between the turbo and s/charger due to its location. The fact that the supercharger is sitting proud near the top of the engine would keep the casing cooler i would expect than the turbo, sitting next to raw flame coming out the exhaust ports. I keep hearing about turbo cars getting a hard run through the hills at night and people saying the turbo case just about glows red. Surely that affects the temp of the air, even though it is rushing through there pretty damn quick? Again, not an arguement, just a query.

[Rollin]

There is a bearing and core between the exhaust housing and the compressor housing, which has an oil supply (which also cools the core) on all turbos, and most now also have a water cooled core as well.

If the transfer of heat was a concern, don't you think the people that build turbos would increase the distance between turbine and compressor housings? Not hard to do, wouldn't increase the space requirements of the turbo a lot etc.

PD blowers aren't as efficient as turbos at compressing/moving air, purely due to their design - the lobes/screws on the rotors etc. Centrifugal blowers are pretty much just the front half of a turbo thats being driven by a belt instead of exhaust gasses, but because they have linear boost delivery, IMHO they are inferior to a properly matched turbo setup.

IE:

Car A has an inline 6, 4 litre, running a correctly sized centrifugal blower, max boost of 10psi. It will only see 10psi up at the top of its rev range, with boost climbing from 0 to 10 from idle to redline.

Car B is indentical to Car A but has a correctly sized turbo, running 10psi. The turbo won't do much off idle, Probably achieve 0"HG manifold pressure at about 2000rpm, then hit 10psi at 2500, all the way to redline.

The "area under the power curve" of car B will poop all over Car A, therefore it will be much faster. And if you want to go faster again, get a bleed valve and up the boost, no pulley changes required.

PB blowers give full boost from idle to redline, but generally they are mounted in the valley of a "V" motor, which makes it very hard to intercool the inlet air, which means you need to run a 'safer' tune than an intercooled car to prevent detonation etc. I think they are also not as efficient at high rpm than a turbo or centrifugal blower, and require more hp to drive them.

[wilb]

I'd like to think of myself as the sort of person that can admit when they are wrong, mistaken or otherwise misled. (gets down on one knee) Rollin, I cry your pardon sir. I would have bet money on the heat affecting the air. At work today, my boss was getting, er, shall we say frustrated, so we rang and spoke to some turbo guys. He said, "you know how to cook?" I asked why "cause your gonna be eating humble pie" He said, the air in a turbo isnt there long enough to get hot. I asked, well what about most turbos these daus seem to haev intercoolers, blowers dont. He said, (remembering that we were being very generalized) trubos run at very high speeds, much higher than superchargers, and as a rule, run higher pressure. Meaning more heat, as you explained in your post. Superchargers (the kind you'd find on a V block) generally run lower pressures and therefore dont build up as much heat negating the need for a cooler. So. me=wrong. I also, on a slightly different topic, was talking to the diesel guys we use. They agreed that the air goin gin to a diesel can afford to be hotter than a petrol, but, they still run intercoolers because at the end of the day, your still looking for as denser air as you can get in the cylinder to make it burn better. Not a correction or an arguement starter, just a footnote. Er. sorry man.

[BLSTIC]

Intake temp is more about efficiency than boost pressure. It is also way easier to have an intercooler when you have plumbing for the compressed air than when you have a cast allow block between the compressor and intake ports.

Intercoolers are pretty much a cheap way to be sure it's right. If you want a (factory) forced induction car to be consistant, day or night, tank after tank, you (can) adjust the boost to adjust the torque output. Installing an intercooler is a good way to make sure that the car will be fine making its 300hp on hot days with a bad batch of fuel in the tank (As you need more boost to make the same grunt, hot air = less dense, while also requiring lower intake temps to avoid detonation due to the hot air and bad fuel.)

This is also why a good factory forced induction car can make so much power so easily, you remove the factory safety/marketing (ie V6 commodore) margins, and run better fuels and treat it nicer to compensate.

If anyone didnt understand that, they also make a good sales pitch (INTERCOOLED turbo diesel) and are great things to polish and show off to your mates.

[Rollin]

wilb - no worries man - as you may have been able to tell by my posts (and user text, under my name on the left), I'm quite keen on forced induction, so I've done a lot of reading

I'd love to have a go of building a twincharged setup...I reckon it would be mad!