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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