40 replies to this topic

[Powersteer]

I read that BMW are applying three turbochargers to their six cylinder engines and one of the turbo will be electrically powered. Anyone has any update on this? If it is true then we can assume that would be an early spool up, anti-lag turbo and to kick up the other two turbos to work pick up quicker. Interesting.

[mariner]

Haven't heard about BMW but in a recent UK article on the McLaren MP12 engine built by Ricardo for McL ( the turbo 600bhp one) the spec. apparently required full boost in 0.5 seconds from applying full throttle.

I am not sure how it compares to other street turbo's but it doesn't sound quick enough for high speed track work as that is about 22 metres at 100mph which sounds like a lot of trqack to be off boost.

Mind you the other arguemnt is that less than 22 metres would be too quick....

[gruntguru]

So less than 1 metre (for a NA car) would be way too quick?

[cheapracer]

apparently required full boost in 0.5 seconds from applying full throttle.

Doesn't matter how they spin it, that's a long time and then there's the problem of how much you get when it does come.

Don't know why they don't go for turbo over supercharging, Toyota and Nissan can successfully apply it to mass production cars and at a 10th the price.

[bigleagueslider]

BMW and Merc use sequential turbos on their diesel engines. The reason being that these diesels can tolerate huge amounts of boost, and a single turbo would not give an adequate combination of response and boost. Gasoline engines cannot tolerate as much boost, so a sequential turbo would not be of much benefit.

As for turbochargers vs. superchargers, the turbocharger is far less expensive.

[gruntguru]

Just sitting back and waiting for the definitive answer from JE.

[jatwarks]

...and one of the turbo will be electrically powered.

Please excuse my ignorance of such things.

Could an exhaust turbine not be used to generate electrical power to drive a compressor turbine?

If the electrical energy is stored the compressor could then work independently of engine revs; optimum boost levels at all revs, controlled by the ECU.

It would also mechanically disconnect the inlet from the direct heat of the exhaust.

[cheapracer]

As for turbochargers vs. superchargers, the turbocharger is far less expensive.

Contradictory - Toyota and Nissan are not expensive brands yet they can offer them and Nissan even on one of it's bottom line products. And I didn't say superchargers, I said turbo over supercharger (both).

Whats going to happen as did with front wheel drive is that turbo lag will become acceptable through mass brainwashing, hell it will get to the point soon that if you don't have front wheel drive and smaller turbo engine with "acceptable lag" you will be a social outcast at parties standing in a corner with the anti-climate change ****.

"s c u m" is a profanity?

Edited by cheapracer, 09 August 2011 - 08:54.

[24gerrard]

Far better to use the turbine to charge batteries use electric traction and do away with the old technology ic engine.
Why bother with all the complications just to go vrrm vrrm.

[Powersteer]

If thats the case then they could simply mount a third exhaust driven turbo with lag minimized from the twin easy spooling turbos assisting it although it does make sense if fuel economy and drivability qualities are soughted. It would get pretty heavy if they were to arrange it with the electric motor providing high end power but having said that, manufacturers today are not too concerned with weight if there is more points to gain. Makes for more curiosity if the electric turbo provides higher end boost.

[DrProzac]

Far better to use the turbine to charge batteries use electric traction and do away with the old technology ic engine.
Why bother with all the complications just to go vrrm vrrm.

Hmm so you're suggesting that using a gas turbine to charge batteries powering the electric engine would be a more efficient than using the same gas turbine to drive the wheels via a transmission?

Do you waste less energy by changing the kinetic energy into electric energy, storing it in batteries to power the electric engine (connected directly to the wheels, I assume) than in the transmission when you use the gas turbine directly? I know that electric engines are highly efficient, but is it really enough?

Edited by DrProzac, 12 August 2011 - 16:18.

[bigleagueslider]

Hmm so you're suggesting that using a gas turbine to charge batteries powering the electric engine would be a more efficient than using the same gas turbine to drive the wheels via a transmission? Do you waste less energy by changing the kinetic energy into electric energy, storing it in batteries to power the electric engine (connected directly to the wheels, I assume) than in the transmission when you use the gas turbine directly? I know that electric engines are highly efficient, but is it really enough?

DrProzac,

It's not just the local system efficiency that you must consider, but the impact on the overall performance of the vehicle and drivetrain. And the actual benefit of such devices can vary greatly, depending upon the type of vehicle and how it is operated. Compound turbo systems have been around for over half a century. And there are many different types, including mechanical, electrical, hydraulic, and pneumatic.

The first commercial application was the Wright R-3350 turbo-compound aircraft piston engine in the late 1940's. Ferrari tried the "Comprex" dynamic wave supercharger on their F1 car in the 1970's. Garrett turbo had a "hydraulic assist" turbo on production diesel truck engines in the 1980's. And there are many electric assist turbocharger/supercharger concepts currently being marketed.

One of the primary causes of "turbo lag" is inertia of the turbo compressor/turbine spool assembly. The compressor of a turbocharger is a dynamic compression device that requires high speeds to achieve its design pressure ratios. Adding a heavy, high inertia permanent magnet rotor between the turbo compressor and turbine would not be the best approach to reducing turbo lag.

The better approach, from a turbo lag standpoint, would be to de-couple the turbo compressor and turbine. Coupling the turbine to a PM generator, and the compressor to a PM motor. Decoupling the compressor and turbine would also permit each device to operate more closely to their optimum efficiencies over a wider range of conditions.

The reason we have not (yet) seen widespread commercial use of turbo compound/assist devices is entirely due to cost.

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[mariner]

Bigleagueslider may be bettter on this than me as he seems to have aerospace experience but at a recent Oshkosh symposium GE had some interesting thoughts on future aircraft jet engine design.

Apparently they can see "conventional" turbo fans getting to a bit above 50% thermal efficiency by detail work and better materials but then that's it.

The next step are more radical turbo jets using variable compressor configurations som as to increase pressure ratios to improve TE.

The step beyond that will make 24garrard glow with pride , or otherwise, as it involves splitting the engine and inserting an electric generator/battery/motor set betwen the power source and the fan drive. This implies locating the power source away from the wing/fans so as to reduce drag. This may require a flying wing design GE suggest.

BTW as I understand it, on an historical note, the "engine on a pod " design which is std today is partially aero in nature ( cleaner thin wing), partially structural ( the engines act as "free" mass dampers to resist twist in those thin wings) and partially USAF WW2 battle experience as the USAF refused the Boeing B47/52 designs with buried engines due to fire risk.

-Back to the future these "electric " engines will , of course, be much heavier than current fanjets but if they cut fuel consumption enough the trade off becomes positive as fuel load is cut so overall weight goes down. The longer the range the more engine weight you can add to gain TE. The big turbo cyclone engine mentioned above was an example of this trade off. Probably not good for a fighter but very logical for a long range bomber ( B-36) or long haul piston airliner ( super connie etc.)

Anyway it interesting ( I think) to see how more radical compressor/impeller solutions are being looked at in aircraft as well as road cars.

[cheapracer]

Hmm so you're suggesting that using a gas turbine to charge batteries powering the electric engine would be a more efficient than using the same gas turbine to drive the wheels via a transmission?

Trains have been doing it with other hydrocarbon powered engines for longer than you have been alive.

http://science.howst...-locomotive.htm

[DrProzac]

bigleagueslider: interesting post, though as far as I understand 24gerrard was suggesting using the turbine to power a primary electric engine, not a compressor for a primary IC engine ;)
I consider hybrid turbocharging as a very interesting technology. It's a shame we won't see such solutions in F1, with all the regulation constraints.

cheapracer: good point, I forgot about the locomotives. Actually I'm not trying to make any point, just asking I wonder if such arrangement is viable also for road or race cars. It's clear that trains have different requirements and different constraints. I do know the advantages of electric engines over IC.

Edited by DrProzac, 21 August 2011 - 10:07.

[24gerrard]

The big turbo cyclone engine mentioned above was an example of this trade off. Probably not good for a fighter but very logical for a long range bomber ( B-36) or long haul piston airliner ( super connie etc.)

I have always liked the super connie as an airliner design.
However the big turbo cyclone engines were not much good in the military application. (I dont know about the Connie).

Tommorow I will be out to lunch with a pilot who flew the B36 on long range SAC missions.
He remembers that on almost all those missions at least one engine gave major problems and had to be replaced.
It gave him many extended 'lay overs' in places like Japan, for which he is eternaly grateful.
The American engines were also less than half as powerful as the British sleeve valved engines of the same capacity at the time.

http://en.wikipedia....lls-Royce_Crecy

Sorry for yet another link to this engine but it is very relevent to the thread.
It had a turbocharger driving an electric generator and produced a THIRD of the aircrafts thrust from the exhaust.
The British aircraft engine industry in the 40s and 50s was way ahead on these technologies and that technology is still probably ahead of current thinking in ic.

Edited by 24gerrard, 13 August 2011 - 20:58.

[Powersteer]

I wonder if anyone has any idea how manufacturers have made some of their turbo engines spool up so early in the rev range like BMW's twin scroll 3.0 turbo spooling up at 1,300rpm VW's too all within 2,000rpm...I remember reading that SAAB use to advance their exhaust valve to open early and get some of the bmep energy to spin the turbo early.

[kikiturbo2]

I wonder if anyone has any idea how manufacturers have made some of their turbo engines spool up so early in the rev range like BMW's twin scroll 3.0 turbo spooling up at 1,300rpm VW's too all within 2,000rpm...I remember reading that SAAB use to advance their exhaust valve to open early and get some of the bmep energy to spin the turbo early.

mitsubishi uses variable camshaft timing to change the cam overlap, short term leaning of the mixture to get the exhaust temps up, and on some models even has supplementary air valve to let air into the exhaust manifold, after the exhaust valve..

there is one more point however... Most of these engines, that show wild torque peaks at low rpm, will do so only if you really load them up hard at idle in a very high gear, otherwise in normal driving you will never feel that torque peak.. it will be more pronounced higher up in the rev range.. In general, the lower the specific power per displacement, less turbo lag you will feel..

[cheapracer]

It gave him many extended 'lay overs' in places like Japan, for which he is eternaly grateful.

I am aware of that and I don't even fly ....

[mariner]

Just to show that dual turbo technology is for more than cars here is the 600+ bhp engine of a top of the range John Deere combine ( a sort of very big version of a JD ride on I guess).

http://www.deere.co....e/s_series.html

See page 34

It also has rather cool cab ( with satellite contolled steering).


See page 12.

[J. Edlund]

If it's not turbine driven it isn't really a turbo but Borg Warner do offer an electric supercharger called the eBooster intended to be used with a conventionel turbocharger. If BMW uses a conventional parallell turbo setup combined with this electric supercharger I guess you can bend the truth a bit and claim to have three turbochargers.



http://www.3k-warner...s/eBooster.aspx

To get boost early most modern turbocharged engine tend to use very compact exhaust manifolds. But variable cam phasing also helps.

Car engines spend very little time on high load, so turbocompound have a limited use while the added cost of the system will be significant. Better to spend the money elsewhere. The main advantage with the turbocharger is that the engine can be downsized while keeping the power output the same.

[kikiturbo2]

of course, compact manifolds, and these days ever increasing use of twin scroll turbos..

it is in fact quite a shock to try to compare 1990. turbocharged 2.0 litre car, such as Lancia Delta integrale, with, let's say, 140 HP per litre in lightly tuned form with stock turbo, to something like an EVO 9 with 200 HP per litre on stock turbo, but which still manages to have max boost 1500 RPM sooner, and keep boosting 1000 RPM later.. with much better off boost performance..

[Powersteer]

Nice posts...

If I were to run a compact exhaust manifold and a longer, more pro-horsepower type manifold at a sustained rpm says 2,000, I am thinking I would be getting the same boost. Would it be safe to say exhaust volume to turbine would be recovered on the longer manifold although having more lag on throttle movement but on a constant slow acceleration from start, long and short manifold would not make a difference? If I was to cruise at 2,000 rpm, will I get the same boost on exactly the same engine and turbo except that the manifold length are different or is there some sort of diaspora involved?

[kikiturbo2]

just speculating but with a longer manifold your exhaust gasses would have more chance to loose some of it's energy...

having said that, tests have shown that longer turbo manifolds tend to work better in high HP aplications..

[gruntguru]

Tuned length runners willl favour specific rev ranges as with NA but the negative effect at other rpm can be worse in the turbo case. Long runners also degrade load transients (increased lag) - long cold runners absorb a lot of energy when the load is suddenly increased.

For steady state running, tuned runners and blowdown utilisation (3 or less equally phased cylinders per turbine nozzle) will dramatically reduce exhaust back pressure and increase power and efficiency.

[bigleagueslider]

Bigleagueslider may be bettter on this than me as he seems to have aerospace experience but at a recent Oshkosh symposium GE had some interesting thoughts on future aircraft jet engine design.

Apparently they can see "conventional" turbo fans getting to a bit above 50% thermal efficiency by detail work and better materials but then that's it.

mariner,

GE, Rolls-Royce and Mitsubishi already make turbine engines that exceed 50% BTE. They are combined cycle, stationary turbine engines used in power plants. These combined cycle turbine engines easily achieve BTE's in excess of 60%.

But as for vehicle prime movers, large, slow-revving 2-stroke diesels are still the most efficient. The reason recip piston engines still have better BTE's than turbine engines has to do with the recip engine's much higher peak cycle pressure ratios and temperatures. While the turbine engine can achieve a greater specific power-to-weight, it's BTE will be limited by the max turbine inlet temps it can sustain. Even with the advanced film cooling and high-temp alloys used in turbine nozzles, turbine engines cannot run close to stoichiometric combustion conditions.

slider

[J. Edlund]

Nice posts...

If I were to run a compact exhaust manifold and a longer, more pro-horsepower type manifold at a sustained rpm says 2,000, I am thinking I would be getting the same boost. Would it be safe to say exhaust volume to turbine would be recovered on the longer manifold although having more lag on throttle movement but on a constant slow acceleration from start, long and short manifold would not make a difference? If I was to cruise at 2,000 rpm, will I get the same boost on exactly the same engine and turbo except that the manifold length are different or is there some sort of diaspora involved?

With a larger exhaust manifold volume you will have less low speed boost. With a smaller exhaust manifold volume in relation to the cylinder volume the pressure inside the manifold will fluctuate more, increase during blowdown and then decrease rapibly, with a larger volume the pressure inside the manifold will be more constant. The latter is better for turbine efficiency (the turbine blade speed ratio will be more steady) while the former make better use of the energy availible in the exhaust as it leaves the cylinder.

mariner,

GE, Rolls-Royce and Mitsubishi already make turbine engines that exceed 50% BTE. They are combined cycle, stationary turbine engines used in power plants. These combined cycle turbine engines easily achieve BTE's in excess of 60%.

But as for vehicle prime movers, large, slow-revving 2-stroke diesels are still the most efficient. The reason recip piston engines still have better BTE's than turbine engines has to do with the recip engine's much higher peak cycle pressure ratios and temperatures. While the turbine engine can achieve a greater specific power-to-weight, it's BTE will be limited by the max turbine inlet temps it can sustain. Even with the advanced film cooling and high-temp alloys used in turbine nozzles, turbine engines cannot run close to stoichiometric combustion conditions.

slider

The turbines that exceed 50% efficiency are all combined cycle plants. In simple cycle they only reach efficiencies of roughly 35-45%. It's also a bit difficult to compare them with turbofans used in aircraft.

[Powersteer]

With a larger exhaust manifold volume you will have less low speed boost. With a smaller exhaust manifold volume in relation to the cylinder volume the pressure inside the manifold will fluctuate more, increase during blowdown and then decrease rapibly, with a larger volume the pressure inside the manifold will be more constant. The latter is better for turbine efficiency (the turbine blade speed ratio will be more steady) while the former make better use of the energy availible in the exhaust as it leaves the cylinder.

So before a long exhaust could build pressure to match the boost of a short system, pressure is lost through the turbo from the open blow through nature of the turbine..while the shorter exhaust will enjoy the speed/pulse of being closer to the cylinder.

[bigleagueslider]

Turbocharger turbines are dynamic devices, so they will always perform best when their incoming flows are as energetic as possible. Dumping a cylinder's high velocity exhaust flow into a large volume exhaust manifold, which immediately reduces the flow velocity, and then subsequently increasing the flow velocity again before it enters the turbine is inefficient.

[gruntguru]

I think all the references to "larger" exhaust manifolds referred to "longer" runners, not larger diameter. Inefficiencies therefore arise from heat loss rather than pressure loss during kinetic energy changes.

Edited by gruntguru, 21 August 2011 - 05:47.

[J. Edlund]

I think all the references to "larger" exhaust manifolds referred to "longer" runners, not larger diameter. Inefficiencies therefore arise from heat loss rather than pressure loss during kinetic energy changes.

Larger refers to the volume of the manifold and not specifically to longer or larger diameter pipes.

Look at the "twin scroll" section below, basically this is what is happening when you make the exhaust manifold volume smaller.

[gruntguru]

JE. The obvious benefit looking at your diagram is the absence of interference from the other cylinder causing high back pressure (higher than boost) during overlap with obvious negative consequences. What is surprising is what appears to be higher average BP which should be lower due to better utilisation of blowdown energy in the twin scroll turbine. Is this real or just the scale of the drawing?

Powersteer was referring to the effects of longer runners - not volume. In fact your diagram would not change with longer runners except for the effects of wave tuning, heat loss and pipe friction. On the other hand a larger diameter would introduce a plenum effect.

If I were to run a compact exhaust manifold and a longer, more pro-horsepower type manifold at a sustained rpm says 2,000, I am thinking I would be getting the same boost.

[Powersteer]

I guess the twin scroll map explains it, was thinking of turbocharging wife's 1.6 petrol mini MPV, its a 4 speed auto on a peaky 125hp 16 valve with about 1400kg to move, with a 660cc turbocharger and a 1000cc from cars that would have a combined horsepower of about 150hp. 10.0:1 compression(no internal modification) and no direct injection means very low boost, maybe 4-5 psi, intercooled. The idea is just to get low down torque. The asymmetrical turbos won't be compound base originally. They'll be two staged low volume and high volume hence low volume would have a small turbo for early spooling to help with fuel consumption. Thought I could get away with a nicely done 2 feet long 4-1 exhaust extractors splitting at the end to the two turbos and having a valve opening and closing the high volume turbo to work on the low volume off boost.

The idea of having a really small turbo for low rpm spool up came from the fact that not only the exhaust turbine is low volume, meaning higher exhaust entry speed to the turbine, but also the compressor turbine being smaller and lower geared(easier to spin a small wheel), like a twin scroll turbo but working both ways, blower and compresor. The earlier idea would have the two turbos working in full when the engine is in the higher horsepower range and needs the same amount of boost but more rp/m means more air, higher volume turbo compensating. I had already designed a free flow volume balancing entry valve that would balance the air volume from the turbos different sizes so one turbo would not be choking the other. Basically it keeps both air velocity by changing the entry size. The valve would be placed either on the plenum entry or intercooler entry. Plenum entry idea was to have two intercoolers one small and one large to compliment the low volume concept but it would be messy and fussy. It would have an entirely smaller and shorter intake path. The free flow volume balance valve would be made by my ex-boss, AutoCAD, MasterCAM'ed then into milling.

Now Mr.Edlund steps in and obviously I'll have to redesign the whole exhaust package because 2 foot long extractors obviously won't do justice to the small turbo. Now I have been thinking to make four free flow valves on the exhaust outlet splitting the exhaust (anyone know if they will get jammed from heat expansion?), closing the high volume first. The small turbo's exhaust extractor would have a much shorter path while also having a much smaller diameter pipe. The problem would be to pre-spool the larger turbo. We don't want to have a sudden boost drop then picking up again. I have been thinking about a semi-compound design where the small turbo's exhaust outlet will return its path towards the larger turbo's exhaust inlet so when the larger turbo builds a bit of boost the split valve would start directing more air towards it and less from the smaller turbo and eventually running the large turbo on its own. The intake would be the same as above but the volume balance valve would be completely shut when the high volume turbo is on full song. I have been looking at Yamaha's EXUP valves on the net and wonder if they have any problems on heat jamming. I am pretty sure the engine bay would look like a laboratory when I get the capital to start it. Since the small turbo is a bit low tech I was thinking of machining its body to adapt ceramic bearing.

J.Edlund, what is EO, IO, EC and IC on the chart? Exhaust opening? Intake opening? Exhaust closing and Intake closing? Just to confirm, thank you.

Edited by Powersteer, 26 August 2011 - 18:11.

[gruntguru]

If you are just looking for a challenge, great, you found one. If you or wife want the car to be on the road more than 10% of the next 5 years while you sort out the bugs - forget it. Buy a car that does what you need or put a roots on the van.
EIEIO - confirmed.

[Powersteer]

And the effect on fuel consumption with a roots? VW runs superchargers but how are they tuned to prevent from high fuel consumption?

[gruntguru]

And the effect on fuel consumption with a roots? VW runs superchargers but how are they tuned to prevent from high fuel consumption?

At 4-5 psi the roots won't draw much power and therefore not hurt consumption too badly. There are some Jap units around with electric clutch too.

[bigleagueslider]

I guess the twin scroll map explains it, was thinking of turbocharging wife's 1.6 petrol mini MPV, its a 4 speed auto on a peaky 125hp 16 valve with about 1400kg to move, with a 660cc turbocharger and a 1000cc from cars that would have a combined horsepower of about 150hp. 10.0:1 compression(no internal modification) and no direct injection means very low boost, maybe 4-5 psi, intercooled. ......

Powersteer,

A couple of points to consider before you hash-up the wife's Mini:

First, just where would you put "2 feet" of 4-into-1 header primaries in a Mini engine bay?

Second, at 4-5 psig of boost, an intercooler would not be of benefit. The boost lag, intake flow losses, weight, cost, etc. would not be worth the small reduction in intake charge temps.

Third, the reason an exhaust turbocharger tends to be more thermodynamically efficient than a mechanical supercharger, has to do with the fact that an exhaust turbocharger essentially functions as an additional combustion cycle expansion stage, while a mechanical supercharger does not.

Fourth, does the "1400kg to move" include the wife's GVW mass fraction? Sorry, just kidding. I'm sure the missus is just as physically attractive as the day you married her.

slider

[gruntguru]

Let's hope she isn't in the habit of checking this forum.

[Powersteer]

All good, and thats problem, 1400kg does not include the wife's mass although for the last two month she has been trying to go lightweight hehe. And now lets hope she really doesn't check this forum.
Original idea was a 2 feet per pipe when four goes into one on a 4-1-2 and the intercooler is a paranoia with having 10.0:1 compression ratio and no direct injection on 7,000 rp/m red line, should I do a humidity check as well and how? Actually also drew up a system that had the low volume turbo's plumbing go straight to the free flow volume control valve.

Don't know if I'll eventually hash-up or wash-up her MPV though, whoops. It is just that, as guru said, a challenge to see how low in the rp/m I can get boost. I'll have to get the cam specs and timing just to see if it might be a lost cause before the external surgery begins.

Original Idea.......

Edited by Powersteer, 29 August 2011 - 21:27.

[Nathan]

Far better to use the turbine to charge batteries use electric traction and do away with the old technology ic engine.
Why bother with all the complications just to go vrrm vrrm.

I don't use a car much for my daily needs so I buy a car more for having fun. So because it isn't as much fun.

[J. Edlund]

JE. The obvious benefit looking at your diagram is the absence of interference from the other cylinder causing high back pressure (higher than boost) during overlap with obvious negative consequences. What is surprising is what appears to be higher average BP which should be lower due to better utilisation of blowdown energy in the twin scroll turbine. Is this real or just the scale of the drawing?

Powersteer was referring to the effects of longer runners - not volume. In fact your diagram would not change with longer runners except for the effects of wave tuning, heat loss and pipe friction. On the other hand a larger diameter would introduce a plenum effect.

When you use twin scrolls on a four cylinder engine, that basically cut the exhaust manifold volume that each pulse sees during blowdown in half. That way you get a higher pressure peak during blowdown, more turbine power and with that a higher boost pressure. So, the higher turbine inlet pressure is quite expected. But this pressure peak occur during when the exhaust valve have opened and the piston is still traveling downward. Then the exhaust pressure rapidly drops, so when the exhaust stroke is finished the exhaust pressure is quite low compared to the boost.

Increase the length of the runners and the exhaust manifold volume goes up assuming everything else is equal.