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

Tue Jan 14 13:24:39 GMT 2003

I've been trying to follow this thread, and am a little confused.

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

Do you have a reference?

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.

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.

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).

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.

 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
> >> >>>>
> >> >>>>
> >> >>>
> >> >>>_______________________________________________
> >> >>>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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