[Diy_efi] RE: Banjo Dis. Pic --- Throttling intake air

Tue Jan 14 14:55:37 GMT 2003

At 07:46 AM 14/1/2003 -0600, you wrote:
>I've been trying to follow this thread, and am a little confused.

Its pretty straightforward if you dont drop context or mix definitions
;-)

>You are saying it is more efficient to control boost by placing a throttle
>before the compressor inlet?

Thats not quite what I said, you are twisting the words (just a little),
I said "... from a control systems perspective... more efficient to
control the nonamplitude variable..." or some such ~`:o

>Do you have a reference?

Its basic control systems theory (and practice I might add) except
as I already said - not used in automotive apps due to commercial
issues.

In essence:-

'Its more efficient to control the power going in than dump whats
been created and going out when it doesnt do useful work'

Opening a wastegate and dumping all that heat and kinetic
energy is not particularly efficient, far better is to *size*
the system (I would have thought) so it never needs to get
to that point.

>The most efficient engine is a NA engine with a wide open throttle.
>Airplane guys have known this for years.  It's an art to pick an altitude
>that offeres the manifold pressure you want to cruise at.  After takeoff
>open the throttle all the way, and leave it there the whole flight.

Sure, dont quite see the relevance, we are in a turbo envirnoment,
hence not equivalent, we are 'controlling' not leaving engine at WOT

>Each time you suck or squeeze air, some efficiency is lost in the form of
>extra heat added to the air, because it takes work to get it through an
>orifice, or to compress it.  Nothing is 100% efficient.

Yes ture, the sun is also very likely to rise in the east tomorrow ;)

>So, if you throttle the intake to the compressor, then air is sucked through
>the throttle, then compressed by the turbo to the deck pressure you want to
>run (two efficiency hits), then after combustion, the exhaust is put through
>a turbine where it is expanded one more time, because the compressor is
>working.  Three places where work is being done (three hits total).

Er yes - sort of but thats mostly a static interpretation, in controlling
boost (where the turbo is sized for it), you are controlling the source
of combustion not the much larger energy in the end product.

>If you throttle the exhaust, bypassing the turbine, you can take the NA
>case, where no boost is wanted.  Of course there is still some loss, because
>intake air still goes through the compressor, getting some heating.  For
>moderate or max boost, only one hit, because if you are boosting, it would
>be assumed your throttle is already completely open.

Assumptions not valid or relevant and you are mixing things up a bit,
such as '...bypassing the turbine, you can take the NA...' this is
a leap with all sorts of implicit assumptions. And your last sentence
in para above is not necessarily the case.

Rather than a traditional cost based approach of wastegate venting,
look at from a control systems perspective.

Is it better to control a few litres of air and grams petrol or a
a lot of litres of really hot voluminous exhaust, which perspective
is most likely to be more controllable and more efficient ?

rgds

mike

> Brian Michalk  <http://www.michalk.com>
>Life is what you make of it ... never wish you had done something.
>Aviator, experimental aircraft builder, motorcyclist, SCUBA diver
>musician, home-brewer, entrepreneur and mostly single
>
>
>> -----Original Message-----
>> From: diy_efi-bounces at diy-efi.org [mailto:diy_efi-bounces at diy-efi.org]On
>> Behalf Of Mike
>> Sent: Tuesday, January 14, 2003 7:44 PM
>> To: List for general do-it-yourself EFI talk
>> Subject: Re: [Diy_efi] RE: Banjo Dis. Pic
>>
>>
>> At 01:51 AM 13/1/2003 -0500, you wrote:
>> >Why? To control boost with a butterfly valve on the intake, you create a
>> >pressure drop, so the turbo must do more work to flow the same amount of
>> >air. Seems as if this would lead to more backpressure.
>>
>> No. Use the existing butterfly - though I have seen some systems
>> which used an extra (large) butterfly in front of the compressor,
>> which had minimal pressure drop, though which I dont favour due
>> to issues of possible vacuum applied to comp seals.
>> For systems with fly-by-wire it makes more sense to use that
>> ECU function also to control boost - that way you
>> can dispense with the exhaust waste gate for improved flow,
>> there would of course be a couple of interesing discontinuous
>> terms in the PID control algorithm for the ECU.
>>
>> >If your talking about controlling boost with the normal
>> butterfly in the TB,
>> >the turbo would create much more boost in the IC pipes than the intake
>> >manifold, creating a low-airflow high-pressure ratio situation, which
>> >usually means inefficiency or surge. Or am I missing something?
>> Seems like
>> >you don't want the turbo to do any more work than it has to - after all,
>> >more work requires more exhaust pressure.
>>
>> No. Because throttling the TB reduces exhaust flow which reduces
>> inlet pressure - its a wonderful feedback system in that the
>> effect you are describing is dynamic with a very short delay,
>> if it is a problem then just use a blow-off valve but I doubt
>> it reaches that stage and of course it depends a little to
>> how large the intercooler actually is. I think, we are led into
>> a somewhat false sense of security by virtue of commercial issues
>> when we have a wastegate bypassing flow around the turbine, in
>> general control systems parlance it makes les sense to do it that
>> way - but is justifiable (so far) because we don't have fly by
>> wire in general user *and* its less expensive to put a wastegate
>> setup in the exhaust turbine casting than alternatives.
>>
>> Without the wastegate paraphenalia the turbo outlet should be
>> operating more efficiently, less turbulence, more laminar flow
>> (as much as can be said for that) - this is one reason (I guess)
>> that some higher performance mods go for a separate wastegate,
>> separate to the cast exhaust housing that is - in contrast it
>> is more expensive and complex to throttle the inlet instead
>> but makes more sense to control the 'unamplified' variable from
>> a 'control systems' perspective and one added complexity would
>> be to handle the turbine speed as a prelim factor to boost
>> control, rate of change of boost/turbine speed rise would also
>> be a factor in the PID algorithm.
>>
>> rgds
>>
>> mike
>>
>>
>>
>>
>> >Grant Beaty
>> >
>> >----- Original Message -----
>> >From: "Mike" <erazmus at iinet.net.au>
>> >To: <diy_efi at diy-efi.org>
>> >Sent: Monday, January 13, 2003 12:31 PM
>> >Subject: [Diy_efi] RE: Banjo Dis. Pic
>> >
>> >
>> >> At 10:14 AM 9/1/2003 -0800, you wrote:
>> >> >Any pic of the current set-up? Your T3 flanged dump is an elbow?
>> >>
>> >> Standard one, nothing special - seems to go straight out
>> >> in line with turbine... I have a 2meg byte pic somewhere have
>> >> to trim it a bit,
>> >>
>> >> >I thought wastegates were used to avoid high engine back-
>> >> >pressure. You were you talking about throttling the turbine
>> >> >not the compressor, right?
>> >>
>> >> No. From a control systems perspective its generally better
>> >> to control the input variable - in this case the air into the
>> >> compressor. I understand why its being done in terms of the
>> >> exhaust, cheap, traditional etc. The current wastegate system
>> >> is a 'bad' compromise for a mechanical throttle coupled with
>> >> commercial issues.
>> >>
>> >> In principle it is more efficient to control the boost
>> >> pressure with the input throttle, not feasible unless you
>> >> have drive by wire - which simplies the turbine/wastegate
>> >> casting and should end up smoothing out the exhaust flow
>> >> not having the discontinuity of a wastegate to mess it up.
>> >> The 'delay' through the engine at speeds capable of boost
>> >> reaching some maxima is trivially short.
>> >>
>> >> Another method is to have an extra ECU-controlled butterfly
>> >> in front of the compressor inlet, but this adds turbulence
>> >> and restriction (a little). In control systems aspects its
>> >> far better to control the pre-amplified variable instead of
>> >> dumping 'power' (post amplified variable) vis a vis exhaust
>> >> pressure after the event so to speak.
>> >>
>> >> >A smooth, gently narrowing pipe can be sufficient muffling to
>> >> >avoid the resonator altogether, it'll bark as your wastegate
>> >> >opens though :)
>> >>
>> >> mmmm, My exhaust is throaty now as its 3" all the way through
>> >> and all the existing resonator is - is just a opened pipe
>> >> with restriction at both ends - though not much. The muffler is
>> >> a 'straight through' - the car goes well and is quiet at highway
>> >> cruise speeds a little noisey when pushing it hard.
>> >>
>> >> PS: Only just saw this email  after some time as it didnt come
>> >> through list, I llok at my list stuff first and am interested
>> >> in any other observations so I'm happy to keep it on list, tah
>> >>
>> >> rgds
>> >>
>> >> mike
>> >>
>> >>
>> >>
>> >>
>> >> >Cheers,
>> >> >Rod
>> >> >
>> >> >-----Original Message-----
>> >> >From: Mike [mailto:erazmus at iinet.net.au]
>> >> >Sent: Thursday, January 09, 2003 9:38 AM
>> >> >To: R.E.Hiorns at IEE.org
>> >> >Subject: RE: Banjo Dis. Pic
>> >> >
>> >> >
>> >> >Unfortunately I have the existing turbo-flange dump pipe,
>> >> >which looks like 2.5". So I have a 'downpipe' which comes
>> >> >from the turbo dump. Its 3" as is the rest of the system,
>> >> >cat, and resonator and tip. Seems to be a heck of a lot
>> >> >better then before and the resonator (basic type) seems
>> >> >to absorb any highway drone (80 - 120Kmh). I havent
>> >> >done a turbo outlet pressure yet - too preoccupied with
>> >> >work. I might get a proper T3 flanged dump next time though
>> >> >I have been thinking of getting a turbo with no waste gate
>> >> >and throttling the inlet instead as boost control, makes
>> >> >more sense from a control systems perspective and its unclear
>> >> >why its not done - other than cost issues, for performance
>> >> >mods vis a vis exhaust flow improvements, thanks for the
>> >> >feedback - I guess I could do a TOP as I have a few gauges
>> >> >around the place, maybe after work calms a bit next month,
>> >> >
>> >> >rgds
>> >> >
>> >> >mike
>> >> >
>> >> >
>> >> >
>> >> >At 09:26 AM 1/9/03 -0800, you wrote:
>> >> >>T3 -> 3" ... if you have no abrupt corner in the downpipe then
>> >> >>you're not doing badly. The easy way to match them is to use an
>> >> >>opening taper in the exducer, and if it's steep enough it'll
>> >> >>cause turbulence to drop out of the helix and give you pretty
>> >> >>much minimum TOP. The angle required is about 30 degrees but
>> >> >>don't quote me on that! Keep the wider pipe for at least a foot,
>> >> >>maybe 2, after that you can narrow slowly to 2.5" if you like.
>> >> >>Have you measured your TOP? You might have no issues to tackle :)
>> >> >>Cheers,
>> >> >>Rod
>> >> >>
>> >> >>-----Original Message-----
>> >> >>From: Mike [mailto:erazmus at iinet.net.au]
>> >> >>Sent: Thursday, January 09, 2003 8:35 AM
>> >> >>To: R.E.Hiorns at IEE.org
>> >> >>Subject: RE: Banjo Dis. Pic
>> >> >>
>> >> >>
>> >> >>At 08:29 AM 1/9/03 -0800, you wrote:
>> >> >>>Hi Mike
>> >> >>>I'll get you a pic later. Let me know if you find one in
>> >> >>>the meantime. IIRC they're as good as a straight pipe.
>> >> >>
>> >> >>OK, tah - I'd like to see some physical issues, size, angles etc
>> >> >>
>> >> >>>Imagine a compressor assembly put up to the turbine exducer,
>> >> >>>except round not spiral, and with no wheel. The gas enters
>> >> >>>axially and leaves radially, so effecting a 90 degree turn in a
>> >> >>>very small space. They're used to avoid sharp corners.
>> >> >>
>> >> >>mmmm - I have a T3 into a 3" exhaust, hence a discontinuity, I'm
>> >> >>wondering if a horn type outlet into the larger pipe from the
>> >> >>small turbine exit would be of benefit ?
>> >> >>
>> >> >>rgds
>> >> >>
>> >> >>mike
>> >> >>
>> >> >>
>> >> >>
>> >> >>
>> >> >>>Cheers,
>> >> >>>Rod
>> >> >>>
>> >> >>>-----Original Message-----
>> >> >>>From: diy_efi-bounces at diy-efi.org
>> >[mailto:diy_efi-bounces at diy-efi.org]On
>> >> >>>Behalf Of Mike
>> >> >>>Sent: Thursday, January 09, 2003 7:40 AM
>> >> >>>To: List for general do-it-yourself EFI talk
>> >> >>>Subject: Re: Banjo Dis. Pic ? Was Re: [Diy_efi] Turbine inlet &
>> >> >>>outletpressures, housing A/Rs
>> >> >>>
>> >> >>>
>> >> >>>At 08:32 AM 1/9/03 -0700, you wrote:
>> >> >>>>>Excuse my ignorance, anyone have a picture of a banjo discharge ?
>> >> >>>>
>> >> >>>>There's a picture of one in the McInnes book. No numbers available.
>> >> >>>
>> >> >>><cough>
>> >> >>>
>> >> >>>As you could probably have predicted, I asked this from an
>> >> >>>internet perspective...
>> >> >>>
>> >> >>>Sorry for not being pedantic,  is there a picture on the
>> web somewhere,
>> >> >>>would someone have a link or have scanned a copy of the
>> relevant page
>> >> >>>(for academic study only;) which shows a turbo banjo discharge ?
>> >> >>>
>> >> >>>rgds
>> >> >>>
>> >> >>>Mike
>> >> >>>
>> >> >>>
>> >> >>>
>> >> >>>
>> >> >>>>Greg
>> >> >>>>>
>> >> >>>>>And anyone have a metric on how much better they are supposed to
>> >> >>>>>be - or are we talking the little banjo fitting on the water
>> >> >>>>>and oil on the turbo ~`:o
>> >> >>>>>
>> >> >>>>>I've done a quick search on google but I seem to get all sorts
>> >> >>>>>of other discharges, mostly medical ones, some with turbos ;-)
>> >> >>>>>
>> >> >>>>>
>> >> >>>>>Rgds
>> >> >>>>>
>> >> >>>>>Mike
>> >> >>>>
>> >> >>>>
>> >> >>>>
>> >> >>>>_______________________________________________
>> >> >>>>Diy_efi mailing list
>> >> >>>>Diy_efi at diy-efi.org
>> >> >>>>http://www.diy-efi.org/mailman/listinfo/diy_efi
>> >> >>>>
>> >> >>>>
>> >> >>>
>> >> >>>_______________________________________________
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>> >> >>>
>> >> >>>
>> >> >>
>> >> >>
>> >> >
>> >> >
>> >>
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