A thought occurred to me. If anyone has a
spectrum analyzer (Steve??) and could obtain an Rotary Knock
sensor - that perhaps determining the frequency response of
the knock sensor MIGHT indicate the frequency band pass
required. Although it is likely to be too broad to be much
help if ( as likely) they do the filtering through a bandpass
filter within the engine CPU.
Ed
Sent: Monday, August 29, 2011 9:54 AM
Subject: [FlyRotary] Not so Simple was Knock
sensor was tune with ADI: [FlyRotary] Re: How to tune with
ADI?
As Tracy also indicated - in may cases,
what initially appears simple - frequently turns out not to
be the case, when you dive into the details.
Another seemingly simple project I thought
about, was to add a wide band O2 (WBO2) sensor option for the
EFISM. This in order to provide more accurate info on the
air/fuel ratio (although one could argue just how useful that
might be for our applications).
While providing an algorithm for the
different voltage input curve of the WBO2 sensor (it is much
more linear than the narrow band O2 sensor curve) is
straightforward, when you dive deeper you discover that:
1. For the wide band O2 sensor to provide
accurate information the sensor temperature must be held
within a critical narrow range.
2. To do this properly, the WBO2
manufacturer either programs into the automobile's CPU or
provides a separate "control" chip that uses a PID
(Proportional, Integral, derivative) the control algorithm
necessary to hold the required critical temperature range.
3. Failure to hold this temp range
renders the sensor output of questionable accuracy and will
lead to degradation/failure of the sensor.
4. The PID temp control is much more
complex than the algorithm required to read the output voltage
So while I could add the WBO2 sensor -
without the separate algorithm (or control chip), the validity
of the data is uncertain and likely misleading. So no WBO2
option any time soon.
Yet this project is much more
straightforward than a knock sensor. Most automobile engine
manufactures can afford to do the research and they can spread
the cost over millions of engines sold. As you might imagine,
the results of their R&D is considered proprietary
information and seldom available to the public.
Ed
Sent: Monday, August 29, 2011 9:24 AM
Subject: [FlyRotary] Re: How to tune with ADI?
What Ed said. There is a knock sensor input on the EC3 but
after finding the same facts as Ed mentioned, it takes a lot
more R&D to implement it so that's why it's currently
unused.
Tracy
Sent from my iPad
The problem with Knock sensors is that
they need to be able to identify the "knock" sound
characteristic of the engine you have it on. The circuit
is basically simple - the challenge is design the
parameters of a signal filter that permits the circuit to
properly identify (filter) the "Knock" charactertistic
of your particular engine.
So I would suggest that a knock system
for a rotary might have different characteristics than for
a piston engine. So what might work fine for a piston
engine might not work so well on a rotary. But, on the
other hand it might work fine.
Ed
Sent: Monday, August 29, 2011 3:45 AM
Subject: [FlyRotary] Re: How to tune with ADI?
Hi Dave
If you are chasing a circuit for knock sensing try:
Cheers
Steve Izett
Perth WA
On 29/08/2011, at 12:24 PM, David Leonard wrote:
Ok, So I have the new ADI system installed and
working.... I think?
Some of you smart racing guys probably have
experience with ADI.
Most of the instructions that come with tuning it
are directed toward car guys that have computers and
knock sensors. All they do is turn the system on and
the computer allows more advance because I is not
sensing any knock. The only real advise I have so for
for me is that I should be running just less than the
amount of ADI that it takes to bog down the engine.
My system is a fixed flow so I don't have much choice
but it seems to be about right. If I use straight
water (which I did for initial testing), the engine
bogs after about 10-15 seconds of ruining the ADI
system. But when I uses a 50/50 mix of water and
denatured alcohol (too hard to find methanol around
here, but close enough) the engine does not bog.
So assuming my amount of ADI injected is about
right, now I am supposed to be able to lean to better
power and advance the timing a little. But how much?
For the last testing flight I was using EGT for lack
of a better guide. When the ADI comes on, my EGT
drops by about 30 deg C, and there is a hint of
roughness to the engine. I can then lean a little and
the roughness clears up. For my test flight I leaned
until my EFT came back up to where I normally limit it
(890 deg C). But if I then add 5 more inches of MAP,
there is still a hint of roughness even at 890 deg and
I get the sense that it wants to be leaned a little
more. But I am afraid to do that... We are talking
45" MAP and 7300 RPM here (185 KTS indicated (Vne) and
climbing at 500 fpm).
So here are my questions:
Is EGT a useful tool here, and does leaning to get
the EGT back to 890 make any sense?
Since Methanol will do such a good job at
preventing detonation, is it safe to lean further
toward best power (peak EGT)? (note, that will be hard
on the turbo... I need to remember to bring the spare
one to Reno)
How much advance do you think i can add? I was
previously ruining 5 deg ahead of Tracy's recommended
initial set up. Can't give a number because the EC2
retards the timing with higher MAP's. How much, I
have not heard. I can easily add one deg at a time
using Ed's EFI monitor. But without a knock sensor am
really in the blind.
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