I agree that your low pressure pulses are due to improper fuel mix at your single point of ignition (since you are using the one spark plug hole for a pressure transducer). The flame front velocity is greatly reduced in improper mix, so the flame front propogation is too slow from a weak initation event.

What are you using for ignition? The spark energy appears to be too low.

What is your ignition timing? Peak cycle efficiency for a piston engine is typically with peak combustion pressure occuring at 12 degrees ATDC, so I would look for 18 degrees on a rotary. It seems that your 45 degree peak pressure is running a terribly retarded ignition.
Have you tried adjusting your fuel mix to improve your combustion?

That is cool that you found some high speed trasducers.I have been wanting to get some for a while now, we use cylinder pressure transducers at work to maximize horsepower and efficiency, as well as emission predictions.

Area under the pressure curve is your friend (indicated torque).

Speaking of that, it is very low. I see where you mention that it is wrong. You should be seeing somewhere around 210 Lb-ft for two rotors, 105 lb-ft for a single rotor based on my output dyno findings.

Your blowdown (pressure at exhaust open) will decrease if you get your ignition timing corrected. Still this blowdown number argues for a later exhaust port opening...

You should see combustion initiation (blue and red diverge) slightly before TDC. (Not too much obviously).

Thank you so much for posting this awesome information! I really like seeing data like this.

Your peak cylinder pressure is low, but very good for 45 degrees (although that is only 30 on a piston engine). I am guessing that this is a 9.0:1 Compressiion ratio engine...

I am guessing that the sensor is in the leading plug hole, as you couldn't read pressure to the end of the power stoke in the trailing plug hole.

I would love to drill an additional hole at the bottom of the housing to monitor so that I could observe effects of leading/trailing split.

I asked them for a cycle to properly map a wankel rotary 1080 deg.
Have they done this Barry? without it the software is useless in my opinion. From memory when I asked this they stopped returning my E-Mails.

Can you map out one cycle at 0 to 1080 deg @ say 5000rpm for me? given where the sensor is this wont be possible sadly, to properly instrument this you would need 3 different pressure sensors equidistant machined into the rotor housing surface and all three sensors would need to be collated into each other to form one map. Me personally I don't care much for mathematical models, it would take allot to run proper sensors all over the engine (internal and other wise to get all the real information of what is happening).

Still It would be good fun to play with, let us know more when you get to test it mate.

The awesomeness of pressure transducer curves is not the math, but that ability to compare curve to curve what improvement was seen by the changes that you just made.

The numbers might not be right, but you really only need to see the 270 degree power stroke to compare the power that you are making at each new setting. The other three should be basically the same at different AFRs and ignition timing settings.

The pressure transducer does not substitute for the dyno, it only allows deeper insight into what the cycle is doing and what adjustments can be safely made.

You are correct about the entire cycle requiring three transducers, but I really don't think that anyone cares about the intake and exhaust stroke, and the end of the compression stroke (all that really matters) is able to be observed. (You might be able to observe the pressure on the intake stroke in the oil injection hole).

This is what I use > http://www.picoauto.com/applications/trium.html

I long ago stopped posting important "current stuff" on the interweb as too many people copied it!.

Anyway I went with picoscope and use it for pretty much everything (actuators and sensors), the amount of stuff you can do with it is only limited by your imagination. Use by lots of OEM big manufacturers too, as In above link.

Why are you guys assuming Barry is only using one spark plug per rotor?

http://www.tfxengine.com/images/SparkplugSensors.gif

Um you realize a bespoke version of one of those is like 5k? I doubt many people would shell out for that least not in forum world :rofl: I looked into it a long time ago, still have quotes probably on it.

Do those combination spark plug + pressure transducer mimic the typical (NGK) spark plugs we normally run?
Mazda went with the surface gap spark plug design for a reason.
Do they have a spark plug that is surface gap also?
I think we all know that shrouded versus unshrouded spark plug electrodes do change the way the engine responds?


-Ted

Ted,
The sensor is a modified Optrand sensor from TFX. It is housed in a special spark plug.
I have two PLX EGTs but the program is calculating the port opening EGTs.



http://i287.photobucket.com/albums/l...6-2663_IMG.jpg

This is my first attempt. It burned up because of the Rotary’s high temps.
Barry


My second attempt (with advise from my mentor) was this .025” orifice to protect the sensor face.

http://i287.photobucket.com/albums/l...s/IMG_8430.jpg

I sent the company who makes them request to make bespoke version in heat range and type I need (modified NGK) and got quoted 5k or 7.5k for one plug only! I decided to not get it lol (things may have changed since then, was 6+ years ago now). Though this was many years ago before I spent 50k on VBOX gear and my Pico scope set up.

The specific multi function super response sensor I use on the Pico is like $1+k only measures to 500psi though or 3.4Mpa can do running tests with it just not high powered ones, I am looking for another sensor that is as accurate and fast (>1% FS) and lower cost lol.

My next engine I will machine the rotor housings to fit three sensors permanently equidistant into the engine and map the whole cycle, see how excited I get haha. Can tell you from running a car permanently VBOX equipped after a year or more of looking at reams of information you do get slightly over it :beatdeadhorse5: Then again I have been doing crap like this since 1991 (beginning of mech eng study), combine that with the internet age now where every single customer/peer is a mech eng enthusiast/expert cause of wiki and forums lol and it gets on your nerves needing to explain shit over and over in a never ending attempt to educate some cunts.

Barry how much are TFX charging now for a system? and the generic plug sensor btw (like the one you have pictured)?

Peter, my EGTs are 2” from the port in a HKS cast divided manifold.

TFX uses calculations for burn rate by watching the pressure rise. We enter degrees for port opening then the calculations give temp and pressure at opening.

My AFRs are measured in the downpipe 18” from the turbo flange.

I am getting some early detonation indications when the peak pressure is located less than 45º ATDC. Clint, "the mentor", says we can check the stock knock sensor for accuracy. Unfortunately my computer cannot run both programs (datalogit & TFX) concurrently.

Some of the specs on the sensor:

Non-linearity & Hysteresis
Full Scale Output
±1% Combustion
±0.5% Non-Combustion
±0.25% Available

Frequency Response
0.1 Hz to 10 kHz
0.1 Hz to 20 kHz
1.0 Hz to 30 kHz

More at
http://www.optrand.com/products.htm

Barry

Titanium,
My understanding of this very preliminary data is that we will have to keep the lower squatter points greater than 45º ATDC (at higher RPM anyway).

I think the main focus may become lessening the reversion from the exhaust port to decrease or minimize the squatter.

Barry

Um, I guess you realize someone on this forum has the means and know-how to make their own now.

I was simply pointing out the error in thinking that only one plug per rotor was being used.

I will discuss with Barry.

Thanks Barry,

Who do you talk to there? you can E-Mail me if you like or PM to save commentary from others, thanks.