[Diy_efi] RE: Throttling intake air -- references

[Grant Beaty]

Great idea and all, but unless you work for a OEM making an ECU for a turbo
car, why bother? External wastegates control boost just fine, my car can run
from 8 psi to over 35.

However the extremely small throttle opening required to hold low boost must
produce a lot of pressure in the IC pipes. When I first put my turbo kit
together I didn't have a dump tube for the WG so I left the boost controller
off and tried simulating WOT conditions by modulating the throttle, and I
noticed I barely had to give it any gas at all; it was actually kind of
difficult. Autocrossing a car that spins through first and second requires
quite a bit of throttle modulation, so I'm used to it.

My WG is currently set to open at 17-18 psi. My boost gauge is plumed into
the intake manifold, and if I modulate throttle, it opens at around 7 psi,
so thats a 10 psi drop across the throttle plate. On some turbos, that surge
teritory, and it does surge a bit on mine. If I had electronicly controlled
everything, I'd modulate the WG more than the throttle to keep it off surge.

Even if there are benifits, just doesn't seem worth the effort.

Grant Beaty

----- Original Message -----
From: "Mike" <erazmus at iinet.net.au>
To: "List for general do-it-yourself EFI talk" <diy_efi at diy-efi.org>
Sent: Thursday, January 16, 2003 1:23 AM
Subject: RE: [Diy_efi] RE: Throttling intake air -- references


> At 10:04 AM 15/1/2003 -0600, you wrote:
> >> Brian,
> >>
> >> You are missing the point totally !
> >
> >Well, perhaps, but you have not provided me with any references to
support
> >your claim.
>
> Brian, I am not making a practical claim from heaps of academic
> reference which you seem to be fixated upon to quantify a judgement
> as to whether you entertain an idea. Its basic control systems
> theory. I dont have my text books from 1980-81 to hand but I can
> tell you its considered far more sensible to control fuel
> before its combusted than after its done its thing. Look at
> rocket engines, jet turbines, they all do what I suggest as do all
> the people that drive turbo cars that use their foot for reducing
> boost - some time before the lossy wastegate needs to be vented,
> its implicit and taken for granted when we dont drive to maximum
> therefore some time *before* the wastegate needs to be vented.
>
> >Again, our regimes are completely different.  I am looking at steady
state,
> >with efficiency as the bottom line I could care less if it took the turbo
30
> >seconds to spool up.
>
> Well dont look at steay state, because thats not relevant or appropriate
> is it.
>
> When you drive and watch boost pressure long before you get to the point
> of high enough boost warranting the wastegate opening you can easily
> and seamlessly throttle back and reduce boost - we all do it, so that
> steady state aspect of your para above is already handled implicitly
> by experience isnt it. I am talking an ECU that handles the transient
> to bring it back via throttling the inlet - effectively the same as
> if you were watching the boost gauge and wanted to back off before it
> went over some magic figure. The issue of spool up is nothing I
> ever suggested, discussed or dismissed, you are adding this and I dont
> know why you are adding complexity to a simple issue, which might
> be relevant admittedly if we were ever in an apples vs apples
> comparison which we have not yet reached ;)
>
> >> We are not talking steady state, we are talking about a control
> >> dynamic - what you tangentially refer to will happen admittedly but,
> >> only in transient for a very shor period of time, then back to
> >> a stready state which is identical to what you do when you drive
> >> normally - which is control the pedal by foot pressure for power
> >> output.
> >
> >Not according to the reference I provided you.
>
> Are you saying your reference is more authoritative than observing
> your own pedal pressure to back off boost, I cant see direct
> evidence for either at this point in time ?
>
> >> When I have my engine on a dyno and I select a throttle level
> >> by foot pressure for say 9 pounds boost (some 1.5 pounds before
> >> the wastegate {relief} opens at 10.5 pounds boost), I can easily
> >> throttle the pedal back a little and reduce boost and repeat
> >> this indefinitely without any problem whatsoever, we do this
> >> *all* the time when we drive.
> >
> >I believe you.  Since your engine is on a dyno, do you have a BSFC for
this
> >specific test?
>
> No, I dont do a BSFC on the few minutes of dyno run, but think about
> it sensibly, when the wastegate opens you are dumping energy - its
> being wasted - hence the name -"WASTE-GATE",  doh !
>
> > I'll bet it's way low.  Also, what is your EGT pre-turbo,
> >and EBP?
>
> As mentioned on several previous occasions which havent sunk in yet,
> "... from a control systems perspective..." Ok, then think about it,
> the turbine turns heat into useful work so if the exhaust is not
> byapssed than useful work is done by all the exhaust, so therefore
> once exhaust is bypassed it much raise the EGT of the exhaust post
> turbine - basic logic as its going around the turbine !
>
> >From another view, measure EGT before and after a turbine, its
> higher before, so if you vent it to after the turbine you *must*
> be raising the EGT after the turbine - basic logic.
>
> >> We do that as a matter of course when driving - and it works.
> >
> >Are all (or the majority) turbocharged cars on the road set with the
> >wastegate completely closed?  If so, please, please give me just on
example
> >that's a daily driver so I can check it out for myself.  I'm not
interested
> >in F1 cars, or any racing example, as the requirements are performance,
not
> >efficiency.
>
> No - of course not, but we are not bang-bang drivers are we, dont you
> ever watch your boost gauge go to say 9 pounds and back off the throttle
> and watch it reduce, we dont *need* to go max out for a wastegate relief
> for an understanding we can back off before that point by virture of
> throttle pressure applied by discrimination through foot pressure...
>
> Ask yourself, is it more efficient to dump exhaust via wastegate or
> have the turbo use this energy albiet at lower overall flow rate by
> virtue of the dynamic of inlet throttling... ?
>
> >> All I suggest is to flick off the wastegate - get better laminar
> >> flow from the improved exhaust geometry post turbo and let an
> >> ECU make the decision to assist me by backing off the throttle
> >> as it gets to the maximum boost selected in such a way that I
> >> cant over-ride it and damage the engine.
> >
> >Why can't the wastegate have it's own exhaust pipe?  Some airplanes do.
> >Mine does.  Great laminar flow, but I'm not sure how much that buys you
in
> >reduced EBP.
>
> Sure we can have its own pipe, I am not arguing against this, I am simply
> saying, in relevance to cast wastegates in turbo bodies, that there might
> be an alternative and from a control systems perspectives it makes more
> sense to control the input rather than the output to control power.
> Adding an external wastegate costs more which makes one wonder if
> its better to avoid stuffing around with venting high temp. exhaust
> when we can control low pressure air and fuel far more easily !
>
> >> That is how turbines from Pratt and Whitney and Rolls Royce do
> >> it, I never knew Cessna made jet turbines - I cant imagine
> >> a wastegate biug enough - but you have to ask - why do cessna
> >> do it when Pratt and Whitney, Rolls Royce and GE dont !
> >
> >I'm not talking about turbine engines, turbocharged piston engine.  Oh,
by
> >the way, Cessna DOES have a line of jet aircraft.  Ever heard of the
> >Citation series?  I think they use P&W engines.
>
> Hang on ! YOU are the one that launched into aero issues, are you
> saying Pratt and Whitney and Rolls and GE use wastegates, surely they
> dont.  In an earlier email you alluded to the point Cessna used
> wastegates on their turbines, now you are saying they use P&W turbines,
> which jet turbines use wastegates then...
>
> And dont you think that if P&W, Rolls, GE dont use wastegates then
> it might make sense why they have gone that route ?
>
> >> Your response to this idea seem woefully dogmatic and you are
> >> going to some lengths to seem to talk me out of it as if its
> >> a real bad idea (and I will answer your earlier posts when I
> >
> >I'm not saying it's a bad idea, I'm just saying your BSFC will suffer if
you
> >control boost pre-compressor rather than with wastegate.  My books back
that
> >up.  I do agree that this would keep turbo lag to a minimum.
>
> No, your books dont back it up, they are tangential and predicated
> on prior art where wastegate turbos were the rage and prior to
> existing control systems methods - they are therefore possibly out
> of date. I've never mentioned turbo lag though it might be a benefit.
>
> >> The '...control systems perspective...' re a reference, well this
> >> is implicit in control systems theory which I studied at the
> >> local uni, I dont have an explicit reference without you entering
> >
> >Which degree do you have?  Which university?
>
> Oh really, in to comparing the sizes of our dicks now are we <sigh>
> think back a few steps so this is not necessary...
>
> WAIT = Western Australian Institute of Technology, did my Bachelor
> of Engineering back in 1982, and my thesis was fuel injection control
> with feed forward transmission control. Studied there for 7 years,
> during which I did electives in AI, psychology, business methods,
> applied diploma in statistics, effective double major, taught 2nd
> year bachelor of information processing students for 5 years whilst
> a student from 1978 to 1982, worked in process control industries,
> blah blah - not relevant.
>
> >I am an instrumentation engineer as well, with a bachelors of Science in
> >Computer Science.
>
> Then it should be abundantly clear to you its not as efficient to
> dump power already generated than control its input in the first place.
>
> >I agree that controlling something with a 20milliamp current loop is
> >superior to a hydraulic amplified servo, but we're talking about very
> >similar forces on the throttle bellcrank, and the wastegate bellcrank.
>
> no. Thats why I made particular mention of fly by wire as part of
> a control strategy.
>
> >Go ahead, call me on the carpet again.  I kept all my books from college
> >from PID design, circuit design and control theory.  Only in the last few
> >years have I purchased my current raft of books on engines from Heywood,
> >Bell, Macinnes, and just last week, bought another ... it was referenced
> >here, I was reading it last night before it put me to sleep.  The title
is
> >something along the lines of "Tuning Forced Induction Systems".
>
> Well sure, but dont assume that *everything* is in books, and if it
> aint broke dont fix it ;), I am suggesting that:- given advances in
> processors and control electronics/servos, it might be worthwhile
> looking at the issue of pre-turbo boost control from a "...control
> systems perspective..." - surely with the same discipline and
> training you must appreciate that, and not be led into commercial
> mass market propoganda forcing you to agrandise an issue as if
> its necessarily the 'right' one because its based on false logic
> in terms of control systems theory - the difference admittedly is
> not huge but *I* am interesting in "the path less travelled"...
>
> >> to engine power - thats it, therefore classic control systems
> >> theory has a great amount to say in terms of application and
> >> the reason its not generally done is predominatly for cost issues,
> >
> >Hmmm, I doubt that.  Politics has a lot to do with that.  The EPA keeps
the
> >MPG bar over the heads of the auto manufacturers.  It's not cost alone.
>
> Sure, and this raises in an interesing point... The longer higher
> EGT occurs the more potential for NOx production, and is more likely
> to happen with a wastegate, when you dont dump power that way then
> you can throttle back even more and reduce integral of overall
> EGT over time for a particular drive cycle. You dont need book
> references to exercise grey matter and make extrapolations...
>
> >> ICE has not even been looked at seriously as a control system
> >> problem. The people at Pratt and Whitney, Rolls Royce are rather
> >> more sophisticated and do see their turbines in that light :)
> >
> >For aircraft ICE, that's certainly the case.  The auto guys are light
years
> >ahead in technology compared to aviation.  It's why I'm here soaking up
> >knowledge on this group.  The turbine/jet guys are completely sensitive
to
> >their fixed costs(fuel).  1% here and there adds up to major bucks saved
on
> >a single flight.  I spoke to an aero engineer who was EIT to a Boeng
> >engineer.  They came up with a vortex generator on the B737 that
increased
> >efficiency some fraction of a percent.  Management was happy, they got a
big
> >bonus.
>
> Well yes, so the impetus to throttle the input of jet turbines
> instead of using wastegates must have an efficiency imperative but,
> I disagreee, aviation guys at Rolls Royce where I last visited in
> Bristol UK, are somewhat far ahead of automotives in respect of
> turbine engine developments. Rolls Royce for example, has modelled
> the whole triple shaft geared turbine through control systems
> modelling and not one wastegate in site !
>
> >I think we are arguing the same thing with respect to turbos, but
different
> >regimes.  I still don't agree with your control implementation theory
> >though.  Doesn't mean we need to get into a fest over it though.
>
> Hey, I dont mind a robust debate and,
>
> No, I see two things with your retorts:-
>
> a. You are bound by tradition to some degree, if a thousand people do
> it then it must be right mentality, and considering an alternative
> goes a little against the grain so you argue against it 'knee
> jerk' fashion.
>
> b. The dichotomy between steady state and transient in a control
> systems dynamic *before* the wastegate needs to be opened is
> something you are fixated *only* as if its steady state which
> it isnt.
> In this respect, watch your boost gauge when you drive up say
> a steep hill and back off the throttle, what I am suggesting
> is in most respects the same thing.
>
> I'm off to bed now, its 1am here and I have heaps of work to finish
> before holidays, plus I'm going to watch the stars eating glaced ginger,
> dried paw-paw and a white wine before bed :-)
>
> 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