Sequential turbo information

[coombsie66]

Originally Posted by Paco You seem to know quite a lot about the subject already, so what are you really looking for? - How they got to validate the high emission standards? - How the sequential process works exactly (which turbo kicks in when)? - How the turbos spool up and how fast? - Which kind of ram-air technology they use for the turbo? Be more precise pls. I have to add that I'm no tech-nerd but just theoretically interested in such matters.

To be honest im not too sure on what im looking for! ops: I hope to find out from my supervisior in more detail what he is after from my review. But in requesting information from all you guys, with every document posted i am learning more and more. Yes i do know quite a bit about it already, but i am not entierly sure on the mechanics of the switchover between the turbo's and eliminating boost drop in the change-over process.
Also, with the very limited exhaust gas flow at such low RPM's and low combustion temps (to reduce NOx) i am interested in the turbine technology employed to harness this relatively small amount of energy, and the way that a small turbo can provide the boost required for the low end torque that the sequential system provides.
I am unsure of how much 'lag' in a tubo is the actuall acceleration of the shaft, turbine and compressor, and how much is to do with the actual turbine design. Ie is the RPM when a turbo spools up determined entirely by the moment of inertia of the rotating componants of the turbo, or the turbine design (if so what elements of turbine design).

Thankyou for the opel information wutputt, i think that is the system that was developed by ricardo that i have some information on. It is interesting to see it in a more specific application. Cheers

Deth: i'll look into that, thanks.

jon_s: No you really dont!!!

[number77]

Originally Posted by mit5005 Originally Posted by number77 twin scroll is a super charger. i've never heard of a turbo one? I think you are thinking of a twin-screw supercharger. And I have also never heard of a twin scroll turbo.

yea i was thinking of the twin-screw. it was very late when i wrote that

[Paco]

but i am not entierly sure on the mechanics of the switchover between the turbo's and eliminating boost drop in the change-over process.

Well, what I understood of the new BMW-diesel turbo is that there is no switch over, but a seamless overlap. The small turbo spools up quicker (an thus provides boost quicker at low rpm, giving power from stationairy) and will work alongside the bigger one until the revs go up to an extent that the bigger one gets all the exhaust-boost to deliver top-end boost. I remember reading that BMW had developped a clever exhaust gas by-pass system that could regulate the propulsion by the exhaust gasses. A valve would shut off pressure to the big one when the smaller one had to do all the work and would gradually disperse the pressure over both and eventually cut off the small one, delivering full pressure to the big one.

Don't forget that all the newest techniques are now implemented (improved commonrail, BMW valvetronic, better injection computer control, improved turbo design and the use of light-weight materials, better exhaust systems and generally smaller tolerances which allow precision engineering). I don't think you can attribute these incredible specs just to innovative turbo engineering; you'd have to paint the big picture of overall engine design progress.
Before all these new techniques, attempts have been made to banish turbo lag, like the Delta S4 which had a combination of a compressor and turbo.

[coombsie66]

^^ yeah, i believe the system they use is similar to the ricardo system that i have information on, what i meant in 'the mechanics of the changeover' is what means do they use to actuate the valve that regulates which turbine the exhaust gas runs too?
Also i am aware of the engine techniques now employed by new high performance diesel engines, things such as valve tronic actually further emphasise the need for the sequential turbo system, as with more EGR there is less exhaust gas energy due to the lower burn temperature. All neccessary for emmisions purposes, but this puts more pressure on the turbo system to be able to 'make something from nothing'. And in transient response therefore the sequentail turbo was employed.

[Wutputt]

Originally Posted by coombsie66 what i meant in 'the mechanics of the changeover' is what means do they use to actuate the valve that regulates which turbine the exhaust gas runs too?

I think but I'm not sure, they regulate in continuously depending on the rpm and maybe also the engine load.

Btw, BMW's Valvetronic system only makes sense on petrol engines, since it eliminates the need for a conventional throttle butterfly valve by acting on the intake valve lift in an intelligent way. So you won't see BMW's Valvetronic system on their diesel engines. BMW's variable valve timing system is called (double) Vanos. Their are a lot of people who mix those two up.

[coombsie66]

^^ Thanks for clearing that up, i was a little unclear. But surely they could use valvetronic on the Diesel engines to aid EGR and the exhaust pulse pattern for the turbo's?

[Wutputt]

Well since Valvetronic only works on the intake valves, it won't influence the exhaust pulses, although maybe a little bit in the valve overlap period. For EGR purposes a variable valve timing system is more effective than a valvetronic system that only can change the lift of the intake valves. With variable valve timing, like BMW's (double) Vanos, you can regulate the overlap time between exhaust and intake valves (the time both intake and exhaust are simultaneously open), and thus influence the NOx emissions since overlap induces internal exhaust gas recirculation. But you probably already knew that.

[coombsie66]

^^ Yeah, i was just unsure of this Valvetronic, i havent heard much about it.
You appear to be very knowlagable on this kind of thing, do you work in the automotive industry, did you study at university?

[Wutputt]

No, I don't work in the automotive industry, but I hope some day I will
I studied mechanical engineering, but keeping up with automotive technology is just some kind of hobby of mine as a car enthusiast.

[adamk24]

I hope I can find some pictures or something I can scan to put some solid info up, but until then I'll just tell you what I know. Im going through my tech. training with mercedes and Im a huge turbo fan, including 8 months of training with diesels.
The diesel engine company Detroit Diesel has been using a system called Ddec for their egine management ever sence ddec 1 was introduced back in 1985. Why this is important is that Ddec 5 (the most current) was released on their series-60 engines late last year, and one of the new additions to the system was Variable Duration and Lift Electronic Controll. (A First for a diesel egnine). Basically it is most similar to i-Vtec used on current Honda K-series engines, but not identicall as it uses rail oil pressure to switch a series of slot ports on and off to chage the Lift and Duration.
Ok, if anyone understood that I'd be supprised, so let me try and explain that a little more clearly. Bmw, Nissan, Ford, Toyota, etc... all use a form of variable valve timing, but with a few exceptions (such as porche's variocam and toyota's celica engine) is most often just retarding and advancing cam timing which, lets face it, makes little real difference in term of performace. However BMW's recent 6-series engine and V-10 for the M cars does use a new set of camshafts. However where the Detroit method is unqiue is that it does not use a seperate set of cam lobes to adjust the lift and duration. It uses small slot ports (think of little sharp blades that slide in and out) that sit on the bottom of the cam rocker. By adjusting which slider the rocker sits on, it adjusts the affective mechanical advantage of the piviot. This means it changes the amount of force it is putting on the valve, there by changing how far and how long it holds the valve open.
Why this system is so revolutionary is it can adjust at any point through out the rev. range to adjust for things like boost pressure, hill climb, excessive wind or resistance, or unexpected engine perforance issues. Basically where the other systems fall short is in there variability, only able to change their valve settings based on engine RPM and almost no other factors. The Detroit Diesel system means that not only can you switch to an almost unlimited range of settings to optimize your intake and exaust, it can take into acount other factors that would affect engine performace, such as the spool of a turbo charger.
Ahhhhh, so I did have a relative point to this babble. But wait there more! Mercedes-benz has also been making a Sequential turbo system on their diesel cars. ( I believe they might already be in production.) as has toyota and Chrysler. However these sytem are largely uninteresting and most similar to the system used on the 1992+ RX-7, where it uses a wastegate to hold a turbo off boost until the boost pressure in the first builds high enough for the larger one to make effiecent power. However Detroit saw the potiential advantages of Sequential turbocharger in their new engines. However, not for responce time or decreased lag times like most automotive applications. They were thinking power!
Heres why (I searched for some info to back up this rant and rembered an article in the american magazine, sport compact car, but the columb was not listed online ) But anyway. Basically when you send Air through the first turbo charger, it gets compressed to say 2:1 ratio (one atmosphere), causing your intake air to be about 29.4 Psi (give or take) because the air around us is already 14.7 psi, your effective boost pressure would be 14.7. What happens when you send that air through another 2:1 turbo again? Why you get 60 psi intake air! In other words, you can achieve increadable boost pressure which you could never effiecently achieve with a single turbo charger. (yeah even if its as big as my head). For those that are not familure with diesel engines, they love boost. The more air you can give them, they happier they are. Because 1) they are compression ignited and 2) they are fuel metered (where a spark ignition vehicle is air regulated by the throttle plate) meaning the amount of fuel injected determines the power output, they are impervious to detonation (virtually). So when a diesel company wants, say .... 750 hp from a 11.7 liter engine (actually a rather lofty request for a diesel engine) Numbers like 100psi of boost start to sound very attractive. The thing is at 750 hp that engine would be making about 6500 ft/lb's of torque.
So I would say one of the huge potiential benifits of sequential turbocharging is its ability to produce huge numbers without going out of its effiecent range, because if you push a turbo past its intended ratio (and we all have ops: ) bad things start to happen.
I'll try and get some factuall sources to back this up, so you can use it in your essay. I'll also ask some freinds to make sure I didnt forget anything or get anything wrong. (looking at it now, thats alot of typing )

[coombsie66]

Originally Posted by Wutputt No, I don't work in the automotive industry, but I hope some day I will I studied mechanical engineering, but keeping up with automotive technology is just some kind of hobby of mine as a car enthusiast.

Ah, cool. Same as me then!! I aint finished my degree yet tho, obviously!

AdamK24: Cheers for the input. Some interesting information that i was unaware of. Surely there is a limit to the boost levels applicable to a diesel in an automotive area, as the strength in the block, bottom end etc needed would make the weight involved inpractical for use in most road cars. Obviously it may have an application in lorries and trucks.
Do you know much on the efficiency and emmisions side of things with diesels? As this is really what the review is aimed at. How the sequential turbo system, and the modern engine technology are used in high performance diesel engines, whilst still complying with stringent emmisions regulations.

Cheers

[Wutputt]

Originally Posted by coombsie66 Surely there is a limit to the boost levels applicable to a diesel in an automotive area, as the strength in the block, bottom end etc needed would make the weight involved inpractical for use in most road cars.

Idd there is off course a limit. But with petrol engines this limit is mostly imposed by the risk of detonation. With diesel engines this limit is more imposed by the strength of the internals af the engine. But you can make those stronger, of course not to infinite strength, but you know what I mean

[adamk24]

Great question, but the anwser is simple. The great thing about diesel engines is sence they are fuel regulated, not air regulated, they will always have waaaaaay more air than is needed for complete combustion, meaning they will be greatly lower on harmfull emissions such as NOx and Particulates. Infact most diesel engines take in about 10x as much air as is needed for complete combustion.
Basically this means that high performance and Low emissions go hand in hand, which is one of the reasons I love diesel engines. The down side is your fuel economy goes in the tiolet when you crank the power
One more thing. On heavily boosted diesel engines making alot of power, some times you will see them putting out huge black clouds of smoke. This is caused by incomplete combustion, meaning the fuel is not completely burned, so a lack of air and an overworked turbo are ushally the cause. Such cars as the Salt Flats top speed diesel truck called "black lightning" and the rally diesel that won pikes peak a few years ago, make massive power on insane boost, but because they are built properly, the air comming out the stack is possibly cleaner than the air that goes in (ok maybe a slight exaggeration )

[coombsie66]

^^ Yeah, i have discussed the increased performance levels of diesels with my supervisor, and this is obviously achievable with increased fueling. As you said tho, Fuel consumption -----> Out the window!
With the huge excess of air in the combustion in the diesel engines, doesnt this increase the combustion temperature (and therefore the NOx levels) a lot? Dont you want the combustion temp, compression ratio etc as low as possible, before cold starting etc becomes an issue?

[Wutputt]

Great post, admak24!

But I'm not with you on this one:

Originally Posted by adamk24 However BMW's recent 6-series engine and V-10 for the M cars does use a new set of camshafts.

As far as I know BMW doesn't have a camshaft changing system like Porsches Variocam Plus or Honda's VTEC or Toyota's VVTL, etc.

On the E60 M5 engine they have a double vanos system but this is only a hydraulically actuated variable valve timing system on the intake and exhaust camshafts.
On some 4 and 6 cylinder petrol engines and the 4,4 V8 of the 645ci they have a Valvetronic system on top of the (double) Vanos system. This one uses an electrical motor to change the angle of an eccentric shaft to change the centre of rotation of an extra rocker arm and thus changing the valve lift. But this system only has the intention to take over the role of the throttle butterfly valve.