[Diy_efi] RE: Throttling intake air -- references

[Brian Michalk]

> >Therefore my interpretation of the graphs and the text means this:
> >If you raise the EBP without a corresponding increase in MAP, you lose
> >power.  Therefore it does not make any sense (efficiency-wise) to have a
> >turbo working against a partially closed intake throttle body.
>
> Brian,
>
> You are missing the point totally !

Well, perhaps, but you have not provided me with any references to support
your claim.
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.

> 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.

> 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?  I'll bet it's way low.  Also, what is your EGT pre-turbo,
and EBP?

> 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.

> 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.

> 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.

> 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.

> 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?
I am an instrumentation engineer as well, with a bachelors of Science in
Computer Science.
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.

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".

> 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.

> 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.

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.


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