AFM measurement/backpressure (was Turbo speed sensor)

[nacelp]

> The condition which is being avoided is that of knock. A knock
> sensor is apparently out of the question to aid in learning the
> engine's response under a range of conditions.

If your only talking  aout one of the acoustic trash sensors.  Try working
out an ionization type, and I'd bet your "idea" would change.

 It is theoretically
> possible that a single knock event can destroy a fragile engine.

??, where did you hear that?.  That is in the realm of not knowing what your
doing, tune up wise.  Theory based on what?

> However, you don't need to run the engine to severe knock
> conditions, and once you've learnt the response, you can use that to
> avoid the knock condition by a safe, but minimal margin.

Sounds like your of the school, of as much timing as possible, rather then
then as little timing as consistent with max HP.  The difference is what
lets engine win races, or live on the street.

he speed of
> deflection of the crankshaft - the knock pressure will cause the
> angular velocity to exhibit a characteristic "jitter". You won't be
> able to measure that easily at the flywheel end - the inertia will
> "squelch" the jitter, but a measurement at the other end could be
> worthwhile if there are no inertial loads there.

Oh, well then the gm strategy of measuring accleration rates doesn't work??.

 sensor if the resolution were high enough.
> Of course, that's an empirical approach...
> The exhaust backpressure determines the internal exhaust gas
> recirculation and hence the remaining displacement to be filled with
> fresh mixture. That's the air-fuel ratio - remembering that the two
> differ by about 400C (if not more) in temperature, making for a more
> volatile mixture (hence the need to retard with more EGR).

Retard with EGR??.  It's inert as far as combustion goes.  The delution, on
higher rpms is being way over stated, or overthought here in my book.  The
is a huge column of gas drawing across the exhust as it opens, and draws
more raw fuel into the exhuast, then there is EGR at higher rpms.  At
cruise, yes there is some, and at idle lots of self egring, but niether are
boost conditions.

> If there's an exhaust valve overlap with inlet, and we don't know
> the exhaust backpressure, then we must measure if the overlap causes
> exhaust to be drawn back into the cylinder, or if a significant
> portion of the fresh mixture is being "scavenged" into the exhaust.
> Enter your trusty O2 sensor. You need it to react fast enough to
> detect a rise in O2 after the exhaust valve to indicate scavenging,
> or to remain "level" indicating only exhaust gases downstream of the
> exhaust valve (obtaining such a sensor's a problem for higher engine
> speeds).

Nope, just tune for best performance.
Your acting like electronics is the end all to performance, and ignoring
tuning.
There is nothing truly trusty about O2 sensors, they degrade with use, are
affected, by temp, fuel, and back pressure.  So you need to worry about
those considerations then also.

We can still calculate the AFR based on our knowledge of
> volumetric efficiency of the engine.
> Prior testing with the engine will indicate appropriate ignition
> timing to avoid knock at a particular AFR for a specific load/boost.

Which again accounts for the backpressure (or lack of it) issue.
Grumpy



ix.com.au
>      http://www.perth.dialix.com.au/~bernie - Private HP
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