[Diy_efi] RE: Throttling intake air -- references

[Mike]

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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