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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