[Diy_efi] RE: Throttling intake air -- references

[Mike]

The thing is Grant, when you are driving, you use your foot and
the throttle plate to regulate power output - hence regulates
boost - without the seeming problems people say will happen.

or am I missing something from that personal experience ?

rgds

mike


At 02:17 PM 15/1/2003 -0500, you wrote:
>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
>>
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