Sequential turbo information

[coombsie66]

Hi guys, my recent literature review essay for university has the title: 'Novel concepts in turbocharging required to ensure compliance with stringent emission regulations, including sequential turbocharging.'

Anyone have any handy links lying about they'd like to throw my way! :wink:
All i seem to find on searches is a poorly written journo cop out of BMW's new sequential system, lacking any detail whatsoever! :roll:
I think vauxhall have a sequential turbo diesel they are developing at the moment, so any details on anthing would be a help.
And no rush, its quite a long term thing (finished for january 2005) so if anyone stumbles upon any info could you be kind enough to post it here.
Has St-Anger left yet? I think he could have a few ideas on the subject! :P :wink:
Cheers guys. :D

[Paco]

Uhm, I suppose that you are not looking for the explanation on how the simple principle of a sequential bi-turbo works?

In short:
The sequential turbo system works by the primary turbocharger receiving exhaust gas from all the rotors to spool faster, therefore increasing low speed torque and helping to remove the dreaded turbo lag. The 2nd turbo whilst spinning is still yet to provide any boost. At a pre-determined speed the 2nd turbo spools up to add full boost. This results in effortless performance in conjunction with the rotary engines natural smoothness & flexibility.


You might try to find tech data about cars that have sequential turbo's, like the infamous Porsche 959, the RX7 and the latest Toyota Supra.


A nice page about turbo-tech: http://www.mazdarotary.net/turbo.htm

[coombsie66]

^^ Cheers, yeah i know the general concept.
Im looking more towards the recent applications of sequential turbocharging to high efficiency low emmisions engines, but retaining the performance. Eg BMW's recent 3.5 straight six bi-turbo.
Basically, reducing the compression ratio allows for lower NOx emmisions, but this in turn means greater lag for a single large turbo capable of boosting to high performance levels at a higher RPM, so a smaller turbo is required for the boosting at low RPM when the exhaust gasses have lower entropy to be converted to the rotational inertia of the turbocharger.

[Wutputt]

I think I have some more detailed info about BMW's 535d engine somewhere lying at home. I'll try to scan/upload it later this evening or tomorrow.

But I don't have any good info about the Opel OPC sequential turbo diesel engine.

[stracing]

is the twin scroll turbo charging the same thing?
i know mitsu and subie uses them in their cars

well heres a little bit of info of twin-scroll
http://www.autofieldguide.com/articles/050103.html
http://www.forcedperformance.net/faq.aspx

[number77]

twin scroll is a super charger. i've never heard of a turbo one?

[stracing]

i know mitsu and subie uses them in their cars

twin scroll is a super charger. i've never heard of a turbo one?

well you're wrong

[coombsie66]

^^ Ive never heard of them being called twin scroll turbo's either. Variable vane technology i believe is the correct name, and unfortunately my supervisor has exhausted that subject, and is therefore looking at the sequential route (hence my essay) so im afraid its sequential turbo info im mostly looking for. I may include some info on variable vane turbine housings.
WutPutt: If you could find that info it would be great! Cheers. :D

[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 :mrgreen: but just theoretically interested in such matters.

[mit5005]

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.

[deth]

try www.sae.org if you havent already, they should have tons of more academic type books and plus you get 20% off books if u're a member...PM me if u want me to buy them for u since i'm currently a member

http://www.sae.org/servlets/productDetail?PROD_TYP=PAPER&PROD_CD=2001-01-0666
http://www.sae.org/servlets/productDetail?PROD_TYP=PAPER&PROD_CD=910010

just as some examples

[5vz-fe]

RX-7, EVO-8, JDM STi all uses twin scroll turbo charger.....

http://www.mazda.com/history/rotary/e3-1.html

They tend to give better response...anyways, just look it up google, there are plenty of info

[Wutputt]

Twin Scroll Turbo's just means the turbo (single one) has a double housing for the exhaust side. So the inlet side of the turbine has two passages. This is only interesting if the exhaust manifold is divided into two parts, so exhaust pulses are min or less separated. The reason for this concept is to reduce turbo lag.

[jon_s]

Man, I wish I had Uni essays like that!

Shame I am of no help what so ever though lol :lol: Good luck on that one mate.

[Wutputt]

WutPutt: If you could find that info it would be great! Cheers. :D
I messed up a little bit saying I had some detailed info at home about the 535d, cause I haven’t, I confused it with an article I have about the E60 M5 engine. I hope to ease the pain with some highres tech-pics I ordered. I’ll receive them somewhere next week.

But I can give some more info about multi-stage turbocharged engines. You already know how the system works and what the point of it is. So I’ll try to give some more detailed info. Sadly I don’t have loads of info, but nevertheless here it goes:


1.9 Opel OPC diesel

Opel introduced a multi-stage turbocharged diesel engine on their Vectra OPC prototype end 2003. This engine is based on Alfa/Fiat’s 1.9 JTD 16v diesel engine. With the multi-stage turbocharging it produces 212 bhp and 400 Nm of torque (@ 1400 rpm). Since the filling efficiency of the cylinders is augmented with the multi-stage turbocharging concept.

http://img13.exs.cx/img13/2899/moteur-twinturbo1.jpg

So how is this system controlled? In below pic gives the scheme of the twinturbo concept for the OPC diesel. Both intake and exhaust have their valves. The one in the intake is actuated by a pressure difference and the one in the exhaust is electronically controlled. The exhaust manifold is directly connected to both big (below on the picture) and small turbo (above on the pictures). The pipe going to the small turbo has a high flow resistance like you can see on the above picture of the engine. The pipe going to the big turbo has a far larger section and lays more inline with the exhaust manifold. But a valve controls the flow going through this pipe.
At the intake side the airflow always passes through the big turbocompressor. After the big compressor the flow can go two separate ways: via the small turbocompressor or just directly to the intake manifold (and thus bypassing the small compressor). Notice also both intercoolers: one between the big and small turbocompressor and one before the intake manifold.


Below 1800 rpm the exhaust control valve is closed. The exhaust gasses can only go through the small turboturbine. Since this one has a low inertia it can deliver a high boost very fast. After the small turbine the exhaust gasses flow over the big turbine, but they only have the energy to let is spin. The big turbo doesn’t produce any boost at this stage.
On the intake side the fresh air passes through the big turbocompressor, but like already said he doesn’t deliver boost. This is why the control valve keeps being closed. So the whole inlet flow has to pass through the little turbo.

http://img13.exs.cx/img13/2428/Opel_twinturbo_1.jpg

Between 1800 rpm and 3000 rpm, the big turbo also begins to deliver boost. Both turbo’s work together. The ECU opens the exhaust control valve a little bit (the ECU opens this valve continuously more for higher revs). So a part of the exhaust gasses drive the big turboturbine. The big turbo starts to deliver boost. But the boost still isn’t high enough to open the intake control valve so all the airflow also has to go through the small turbo. This phase is explained in the below scheme.

http://img13.exs.cx/img13/3205/Opel_twinturbo_2.jpg

And finally under full load and above 3000 rpm the ECU opens the exhaust control valve fully. Since the pipe going to the small turboturbine has a high resistance almost no exhaust gasses will follow this path and the small turbo will just spin without delivering boost. On the intake side the big turbocompressor can deliver enough boost to open the intake control valve. The big turbo can blow the air straight through both intercoolers since the air doesn’t need to go through the small turbo. The big turbo can deliver enough flow to ensure loads of power. The below scheme illustrates this phase.

http://img13.exs.cx/img13/4765/Opel_twinturbo_3.jpg


BMW’s 535d

This one is actually gone into production. This 3.0 sixpack diesel produces 272 bhp (@ 4400 rpm) and 560 Nm of torque (@ 2000 rpm). This engine is extremely high revving for a diesel but already gives 500 Nm of torque free at 1500 rpm. These facts give away the main advantage of this engine: it can rev high and have a lot of power (for a diesel) due to the big turbo but it also has loads of torque at low rpm thanks to the little blower.

http://www.germancarfans.com/photos/3020912.003/1238.jpg

The main concept of the 535d engine and the way it works is exactly the same as for the OPC diesel. But there are some differences. Firstly the valve controlling the flowratio between the little and big turbo in the inlet is not automatically controlled by the pressure difference like the OPC engine, but is electronically controlled by the engine ECU. Secondly the exhaust pipe between the little turbo and exhaust manifold doesn’t has such a high flow resistance as with the OPC diesel. But it still is higher compared to the exhaust gases going from the exhaust manifold to the big turbo. And finally in contraire to the OPC diesel there’s only one intercooler, positioned after both turbocompressors.

Highres detailed tech pictures will follow later on.

[coombsie66]

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 :mrgreen: but just theoretically interested in such matters.

To be honest im not too sure on what im looking for! :oops: 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 :D

Deth: i'll look into that, thanks.

jon_s: No you really dont!!! :wink:

[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]

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 :oops: ) 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]

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 :D

[Wutputt]

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. :wink: 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 :wink: )

[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:


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.

[coombsie66]

Doesnt the Vanos system allow for a wild cam profile (high lift) to be used without the disadvantages at low RPM that these bring, as the duration can be changed constantly.
What is the advantages that a variable valve lift can bring on top of this?

[adamk24]

My mistake. I had been told by a friend that the BMW system was very similar to VVTI or others which uses a different set of cam lobes, but its always good to learn something new! As far as vanos is, Im not to familure with that system. :? But you described it pretty well. thanks! :D

[adamk24]

Oops forgot to reply to coombsie66, yes intake air temp does start to cause problems when it gets to hot, but thats why just about every diesel today uses intake charge coolers (intercoolers) or some other form of retardant/coolant to help reducing intake temps. However, because the ideal running temp of combustion for a diesel engine is 750 degrees F, temperature is not really a consern. And also because diesel fule is much heavier and more powerfull (contains alot more BTU's per liter than gasoline) it tends to burn cleaner.
That reminds me of 1 important factor I forgot, which was fuel quality. One of the most important things in what comes out (emitions) is what goes in, and if the fuel used contains alot of sulfer or barocarbons than it is difficult to reduce emitions further :? But cold starting shouldnt be an issue with most diesel engines. They have intake charge heaters, which is basically the element off your stove used in the intake manifold to heat the air, as well as fuel heaters and glow plugs, all aimed at getting that 750 degrees quickly 8)

[coombsie66]

Yeah, sorry i mean the actual temperature of combustion, not the intake temps, im aware of charge cooling etc, and the heating glow plugs in modern diesels, just surely the compression ratio is lowered to a point where the engine struggles to start?

[Wutputt]

Doesnt the Vanos system allow for a wild cam profile (high lift) to be used without the disadvantages at low RPM that these bring, as the duration can be changed constantly.
What is the advantages that a variable valve lift can bring on top of this?
Well with a variable valve timing system you can only change the phase (get some more advance or retarding the timing), like adamk24 already said. So the cam is still the same, thus also the lift and the duration of opening are. If you advance the opening time of the valve for example 10°, the closing time will also shift 10° earlier. So with variable valve timing you can only shift the opening and closing times of the valve in the same direction and you can’t change anything about the duration of the opening.

At high rpm you retard the timing of the intake valve so it will close very late to get an advantage out of the ram effect of the incoming air. At high rpm the incoming are has a high velocity so even when the piston is already going up, air will still flow into the cylinder.
At low rpm you haven't the advantage of the ram effect, so you have to close the intake valve early. But there is an exception. When the engine is running idle, the intake valve may not close to early since otherwise it will also open early, which causes a big overlap between the opening of the exhaust and intake valves. At idle a big overlap gives a very 'unbalanced' running engine.

So what about variable valve lift systems? It are actually cam changing systems. At high rpm they use a different cam profile, with higher lift and a longer opening time of the intake valve. So more air can enter the cylinder and the engine can breath better. Since the intake valve is open for a longer period and the valve is opened a bit more (other lift) than with the variable valve timing system, more air can enter the cylinder.
Most variable valve lift systems have one cam profile for low rpm and one for high rpm (longer opening, more lift). Examples are Honda's VTEC, Porsche's Variocam Plus, etc.

BMW's Valvetronic system is a little different since it doesn’t use a different cam and it isn't really intended to change the valve lift 'an sich' but to regulate the incoming flow like a throttle butterfly does. By interacting continuously on the lift of the intake valves it can regulate how much air (and fuel) the cylinder enters, and thus act as a throttle regulating system.

[Wutputt]

My mistake. I had been told by a friend that the BMW system was very similar to VVTI or others which uses a different set of cam lobes, but its always good to learn something new! As far as vanos is, Im not to familure with that system. :? But you described it pretty well. thanks! :D
Well the Vanos system works like pretty much the same as most of the variable valve timing systems: use some hydraulic pressure that interacts on a lob of camshaft at the drive belt to rotate the camshaft somewhat.
Double Vanos also uses hydraulic pressure but it pushes a helicoidally gear forwards or backwards to change rotate the camshaft a bit.

And Valvetronic uses an extra rocker arm and eccentric shaft like this:

http://users.skynet.be/fa344132//vt_design6.jpg

[coombsie66]

Ah, sorry i thought that the camshaft could be advanced/retarded quickly enough that the duration of the cam could be effected by the variable valve timing. I see now.
Nice sketch but i dont really undstand the working of the valvetronic still! :oops:

[graywolf624]

That reminds me of 1 important factor I forgot, which was fuel quality.

the number one reason america doesnt use diesel while you europeans do.
Americas diesel is less refined and additionally comes from a source with far higher sulfur content. As such it actually pollutes more then its gasoline alternative(in general).


they will always have waaaaaay more air than is needed for complete combustion

I have to take issue with your wording.
Depending on how you tune a diesel you can reach a point at the higher rpms where the car is choked for air. That is where the turbo charged diesels come in. Thus you can tune the car so at low rpm its not running with too much air per fuel(lean) and at high rpm its not chocked.. (rich).

The double systems work with a bypass valve. Which also works to adjust how much actual air is getting to the system.. controlling these rich and lean points better across the spectrum.

[coombsie66]

Ah graywolf! I was wondering how long it was till you put you finger in this pie!! :wink:

Im guessing the 'cost' issue also has something to do with why us europeans use so much more diesel than you guys! :wink: :P

[graywolf624]

Im guessing the 'cost' issue also has something to do with why us europeans use so much more diesel than you guys

see I was saying why we dont.

We all know why you do.. I dont envy you. lol

[coombsie66]

lol, yeah, i still havent succumed to that, but i swear those 330d's that keep whooping my ass, and still get ridiculous MPG are looking more and more tempting!!

[adamk24]

Again I can see how my wording could be confusing. Later in that post I talked about how incomplete combustion can lead to excessive emmisions and black smoke, but when i stated that it will always have way more air, I was talking from a non-modified stand point. All stock diesels will always get way more air than they need for combustion. (or at least they should) Anyway, what I was trying to get at graywolf624 was that unlike a gasoline engine, diesels are not resticted in how much air they can have.
Which leads to coombsie66's question. The anwser is no, but I the reason that you ask is because you need to understand the way in which combustion works in a diesel engine.
All diesel engines sence..... well sence a really long time ago, have all used direct injection. This means that the fuel injector is in the combustion chamber (ok some times a pre-combustion chamber is used but lets not get complex) and it injects the fuel in a fine mist right into the compessed gasses to cuase combustion. The reason diesel's dont have detonation like gasoline is actually three fold.
First, diesel fuel is far less combustable than gasoline, but it contains more energy (btu content). Because of this resistance to combustion, it is less likely to ignite before it was planned (pre-igniton/knock/detonation). Think water injection or methonal injection. Its a combustion inhibitor.
Second, Because the fuel does not travel through the intake manifold and into the cylinder through the valves, it does not get super heated and ready to explode, like gas does, before it enters the cylinder. Now before you post back, yes I know the injector gets very hot, but because only around 15% of the fuel that goes into the injector is injected before it is sent back to the tank, the fuel does a good job of keeping the injector pretty cool.
Third, because the timing of injection is determined based on alot of factors, they can inject sooner or later to cause ingnition exactly when they want to.
This may or may not be important, but just so you know, diesel engines do not inject all thier fuel in one big spray like a gasoline engine does, they have an initial combustion starting spary (very fine mist), then a pause then they spray a jet of fuel (less fine) into the flame front of combustion to keep cylinder pressures up. In a gas engine, you get one big bang then as the piston travels down, you lose pressure and there by the torque of the stroke. Where a diesel makes its massive torque is from (well its fuel in part because of its increased thermal content) is that it keeps injecting fuel for a majority of the stroke to keep torque up for the entire travel.
Neat stuff, and one of my reasons why I think a diesel is a fundimentally better design. Just like rotary engines! :lol:

[Wutputt]

Later in that post I talked about how incomplete combustion can lead to excessive emmisions and black smoke, but when i stated that it will always have way more air, I was talking from a non-modified stand point. All stock diesels will always get way more air than they need for combustion. (or at least they should)
I'm with you on this one. Stock diesel engines for passenger cars idd always run with an excess of air, even when their emitting soot. This soot emission is cause by an uncompleted burning of the diesel. This is something that can 'easily' happen with a diffusion burning process like with diesel engines (in contrary to the pre-mixed burning process of gasoline engines). If one looks at the whole cylinder there will be an excess of air even when the engine emits soot.

[Wutputt]

Nice sketch but i dont really undstand the working of the valvetronic still! :oops:
The Valvetronic works as follows:
The eccentric shaft is the little thing upper left, the camshaft is positioned right and the extra rockerarm is the long piece in between those two. By rotating the eccentric shaft clockwise the turning point of the extra rockerarm will be shifted more to the right. When this happens the end of the extra rocker arm moves deeper and so the valve will open more (= lift of the valve is increased).

Since the Valvetronic system doesn't use another cam to generate the variable lift, it can continuously change the valve lift. And so, it can regulate the amount of air/fuel mixture entering the cylinder. With more valve lift a lot of air can enter the cylinder, with less valve lift less air can enter.

Now in practise all BMW Valvetronic engines are also equipped with the Vanos or Double Vanos variable valve timing system. Both systems can operate totally independant. But my guess is the Valvetronic algorithm in the ECU will also change the valve timing a bit to further enhance his throttle regulating capabilities.

http://users.skynet.be/fa344132//vt_design6.jpg

[coombsie66]

Ah, ok i kinda get you wutputt.

Adam K24; do you know the reasons for the large soot emissions in teh transient response of diesel engines. I guess it is due to the lack of instantanious boost pressure at rapid throttle pedal changes, and therefore the fueling is equivalent to that RPM at full boost rather than that RPM at whatever boost is specific at that moment in time.

[graywolf624]

it is less likely to ignite before it was planned (pre-igniton/knock/detonation)

to explain this better for our less technically inclined.

When gas or diesel is ignited it travels on a front.. aka a line that slowly progresses along the area.
Preignition.. is when the gas not on that front(beyond it) ignites due to heat. (causing an uneven burn)
In a diesel engine.. the ignition is actually done by pressure and heat.. while gas is done with a spark.

The benefit obvious from diesel besides btu content is the efficiency at 0 due to the unrestricted airflow by the way.

Just clarifying.. you seem to be doing a good job of describing.

[adamk24]

do you know the reasons for the large soot emissions in teh transient response of diesel engines. I guess it is due to the lack of instantanious boost pressure at rapid throttle pedal changes, and therefore the fueling is equivalent to that RPM at full boost rather than that RPM at whatever boost is specific at that moment in time.

Well actually, although that IS the reason (some of the time) the anwser my diesel pad instruction would give is no. Heres why.
In most modern diesel engines designed for large trucks and heavy equipment they have sensors to monitor things such as boost pressure, atmospheric pressure, injector pulse width etc... they can adjust fuel to follow what ever conditions the engine is currently running under, not just following a pre-determined fuel map, like most automotive engines. But yet, when you get in a diesel and step on it, it shoots out black soot. Why? Well basically these systems do not work as good as they claim to, and despite the sensor shouting at the ecu "Uhhhh.... we dont got boost yet idiot, lay off the fuel!" it tends to have a slow reaction time. So, yes, its because the engine expects boost, but it takes it a while to realize that it doesnt have it, but by then the turbo is spooled and everything works out.
The real question I have is why does it take so long for it to figure out that it is over fueling? I will ask my diesel instructor tomorow and see what he says, but logic would tell me that if a computer can adjust the spray of fuel, messured in milliseconds, over 100 times during a spray no longer than 15-30 milliseconds, then why does it take it over 1/2 a second to turn down the spike of fuel :?: :? :?:

[Wutputt]

but logic would tell me that if a computer can adjust the spray of fuel, messured in milliseconds, over 100 times during a spray no longer than 15-30 milliseconds, then why does it take it over 1/2 a second to turn down the spike of fuel :?: :? :?:
Maybe the response time of some of the sensors used to determine the exact amount of fuel injected is quite slow when there are some bigger changes, like when you suddenly step on it.

It's just a guess.

[coombsie66]

U find out nything more adamk24?

[adamk24]

Yeah I talked to my instructor last week and basically what he told me is that they pre-program an intentional overfueling when you mash the gas before the engine is at operating temp for two reasons.
First to help with faster catalitic converter light-off, and also to give a margin of safety to prevent underfueling when switching to the new higher load % fuel map. Basically that means injecting more fuel before retarding injector timing to help prevent detonation. (because the injector timing is what helps prevent detonation in a diesel). If there is anything else that you need to know about turbo systems or diesels feel free to ask :mrgreen: