EGT and O2 sensors time resolution

[Diehl, Jeffrey]

I was jsut about to ask the VERY SAME QUESTION!  I can't believe that this
isn't documented somewhere.  Perhapse on the spec sheet?

Anyway, there were threats of doing the math... I guess I missed it, so here
is my attempt.

At 7500 RPM, we have 125 revs per second, each lasting .008 seconds.  We
have an exhaust stroke every other rev, or .016 seconds apart.  At this
point, I'm assuming a probe on EACH exhaust runner.  If you "choke" the
exhaust through a single exhaust, (sorry, couldn't help it.) then your
exhaust pulse rate will be 4, 6, 8 times this rate.  Clearly 10us is too
slow to detect an exhaust pulse if you only have one probe, and it's barely
quick enough if you have 4,6,8 probes.

Am I missing something?

Mike Diehl.

-----Original Message-----
From: Bernd Felsche
To: diy_efi at diy-efi.org
Sent: 9/12/2001 6:37 PM
Subject: Re: EGT and O2 sensors time resolution

Santi Udomkesmalee tapped away at the keyboard with:

> 2 questions...
> 
> 1)  What sort of time resolution do EGT sensors, and O2 sensors have?

O2 sensors can be faster than the stream of exhaust gas from the
valve. Depending on type, placement and temperature, you're looking
at response times in the region of 10 to 100 milliseconds.

EGT depends a great deal on the type of sensor and the exhaust gas
temperature _gradients_. i.e. how quickly they rise and fall. The
sensor has a finite response time dependent on its thermal mass.
Response time to reach a "near enough" reading can be in the
seconds.

> 2)  Would a closed loop system be benificial to a high performance
> application?  That is to say, ideally the engine should be at WOT
> or idle most of the time.  Would there be any gains to
> implementing some sort of closed loop system in this application?

What sort of high-performance application? Aircraft?

Just the usual benefits:
Engine life, mainly. Also fuel consumption and engine power
optimisation along with emission control.

Other main benefit is that it allows more aggressive control
strategies.

BTW: An engine should never idle. That's 0% efficiency. :-)


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