In Chamber Testing

[Barry Bordes]

I have been working with pressure sensors to try and understand what is going on inside the rotor chamber.
What I am finding is that the best peak pressures seem to be located around 45° ATDC.
But notice the variation of cycles. We think of a more even flow of power pulses.
This log is taken while accelerating through 5000 rpm. The range above this is still too retarded.

http://i287.photobucket.com/albums/ll129/bbordes/pressurelocation.jpg

[Barry Bordes]

The test equipment is made by TFX Engine Technology.
You can familiarize yourself with the program by going to http://www.tfxengine.com/hardware3.html

The test mule is a RE 13b running 12 psi (10 psi spring)
TO4s, HKS cast divided
50/50 meth water pre and post turbo.
HKS Twinpower
Power FC

[Barry Bordes]

More interpretation.
The red arrows indicate an engine misfire (in this case the mixture was too rich) .
The blue arrows depict a too retarded cycle at about 60° with subsequent lower pressure.
The green arrow show a cycle closer to 45° and higher pressure.
I am amazed at the scatter.

http://i287.photobucket.com/albums/ll129/bbordes/pressurelocation-1.jpg

[Barry Bordes]

Just roughly looking at this chart I would say we should add a degree to section 2 and two degrees to section 3.


http://i287.photobucket.com/albums/ll129/bbordes/pressurelocation-2.jpg

[Barry Bordes]

http://i287.photobucket.com/albums/ll129/bbordes/combustiondetonationrating.jpg


This is what the burn rate looks like. (One of the best examples of the 210 samples taken during this log.)
The red line is the pressure of rotor compression without ignition.
The blue line is ignited pressure.
The purple line is the temperature of the burning mixture. Notice it is still 1400°C when the exhaust port opens.
The pressure at exhaust port opening (EOP) is 91 psi.
A detonation rating of 65/88/0 shows up for this #64 cycle. Since it has 0 frequency I am assured by the Mentor that it is benign. (But whenever the peak pressure is advanced below 45° it gets some of these readings.)
The HP and torque readings are off in this sample because I am using the wrong displacement calculations.

Barry

[RETed]

Wow, I dunno how I missed this, but thanx for sharing such wonderful data!

Do you mind me asking where the location of the pressure and temperature probes were?


-Ted

[RICE RACING]

Can you please show me where and how the sensors (pressure) are fixed into the rotor housings.

Where is the EGT sensor located? what type is it. What calculation (model is used) to guess the temperature at places aside from where a physical hard measure is taken?

How are you measuring the AFR exactly.

I thought about using their stuff but they could not answer any of my more detailed questions on their systems so I left it alone, interested to see what you have found and if you can shed any light on the above and also what cross checks you use to validate the outputs from their equipment.

[TitaniumTT]

First time seeing this as well. Nicely done. Care to comment on the last output and advancing the timing to move the peak pressure closer to TDC? Or do you feel that doing so would lead to a much higher chance of detonation?

I've always wanted to play around and learn more about what is going on in the chamber itself. I feel a better understanding will lead to more power/reliabilty. Seeing what's actually going on rather than reading and interpreting what the engine is spitting out.

[vex]

If I had to guess the pressure sensors are directly bolted in to the combustion chamber via a spark plug hole as I doubt he's using MEMS. Temperature of the combustion chamber could be taken almost directly by placing a temp sensor on the housing immediately outside of the combustion housing (ie in the coolant flow). This would allow the modeling of the temperature fairly easily, though would be rather troublesome to do.

If what I said is true then I wonder how the pressure transducers affect your readings.

[RETed]

If I had to guess the pressure sensors are directly bolted in to the combustion chamber via a spark plug hole as I doubt he's using MEMS.
You'd think this would be an automatic, but this presents one problem...
This will almost always affect the spark ignition due to changing the location of the spark (plug).
It might be a minor thing, but this might throw the data off just enough...


-Ted

[Silver86]

wish i could see the pictures at work...

[vex]

You'd think this would be an automatic, but this presents one problem...
This will almost always affect the spark ignition due to changing the location of the spark (plug).
It might be a minor thing, but this might throw the data off just enough...


-Ted

My thoughts exactly. IT's a pity we can't have pressure transducers directly on the faces of the apex seals or combustion tub.

[classicauto]

Yes if memory serves, Barry's sensors are the sensor/spark plug type.

This is awesome data, and could lead to some very neat results. Its just a pity that all of this data is essentially going to be setting up a bench mark being that no one's really looked at this - in the capacity of the end user - before.

Barry, have you done any comparisons yet between pressures with and without water? Can't recall if I brought that up at deals gap.....

:)

[dudemaaan]

Interesting thread, subscribed

[Herblenny]

Awesome!

Thanks for sharing Barry! Next time I see you, I need to pick your brain again!

[NoDOHC]

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.

[RICE RACING]

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.

[NoDOHC]

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).

[RICE RACING]

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.

[C. Ludwig]

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

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

[RICE RACING]

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.

[RETed]

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

[Barry Bordes]

Wow, I dunno how I missed this, but thanx for sharing such wonderful data!
Do you mind me asking where the location of the pressure and temperature probes were?
-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/ll129/bbordes/126-2663_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/ll129/bbordes/IMG_8430.jpg

[RICE RACING]

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

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.

[RICE RACING]

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

[Barry Bordes]

Can you please show me where and how the sensors (pressure) are fixed into the rotor housings.
After the above failurs
Where is the EGT sensor located? what type is it. What calculation (model is used) to guess the temperature at places aside from where a physical hard measure is taken?

How are you measuring the AFR exactly.

I thought about using their stuff but they could not answer any of my more detailed questions on their systems so I left it alone, interested to see what you have found and if you can shed any light on the above and also what cross checks you use to validate the outputs from their equipment.

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

[Barry Bordes]

First time seeing this as well. Nicely done. Care to comment on the last output and advancing the timing to move the peak pressure closer to TDC? Or do you feel that doing so would lead to a much higher chance of detonation?


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

[C. Ludwig]

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.

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.

[RICE RACING]

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.

[RICE RACING]

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

Thanks Barry,

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

[RETed]

Do we really need to turn this into a playground spat?
Can we drop the name calling?

This thread is GOLD.
Anyone who understands the data being presented knows that this kinda stuff is PRICELESS.
I think this is the first time I've seen such data on ANY RX-7 type of forum.
I've only read about stuff like this is SAE papers.
To have a member actually messing around with such equipment is just unheard of.

It would be sad if this thread gets closed.


-Ted

[Barry Bordes]

If I had to guess the pressure sensors are directly bolted in to the combustion chamber via a spark plug hole as I doubt he's using MEMS. Temperature of the combustion chamber could be taken almost directly by placing a temp sensor on the housing immediately outside of the combustion housing (ie in the coolant flow). This would allow the modeling of the temperature fairly easily, though would be rather troublesome to do.

If what I said is true then I wonder how the pressure transducers affect your readings.

You'd think this would be an automatic, but this presents one problem...
This will almost always affect the spark ignition due to changing the location of the spark (plug).
It might be a minor thing, but this might throw the data off just enough...


-Ted

Yes if memory serves, Barry's sensors are the sensor/spark plug type.

This is awesome data, and could lead to some very neat results. Its just a pity that all of this data is essentially going to be setting up a bench mark being that no one's really looked at this - in the capacity of the end user - before.

Barry, have you done any comparisons yet between pressures with and without water? Can't recall if I brought that up at deals gap.....

:)

Vex Ted and Classicauto.
Not using two plus per rotor would definitely invalidate the findings.

My third iteration spark plug is a –10 heat range TFX model, with a platinum electrode.
The only negative effect that it might have on combustion is that it is ¾” vs the Rotary designed reach of 7/8”.

Things to be tested are: with and without water, water/meth, splits, negative splits in vacuum, advance curves, port shapes, you name it.

Barry

[Barry Bordes]

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.

Two plugs per rotor are being used.

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

Twinpower, only misfires on rich fuel and heavy water/meth levels.

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?

Paul Yaw quotes Yamamoto as 45º ATDC being the point of peak pressure. My tests seem to concur so far.

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.

Correct, I need two more sensors to read full cycle. One in the exhaust port and on in the intake port (which then can test tuned lengths and overlap pressures).

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.

We see both from the leading sensor location.


Barry

[Barry Bordes]

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-Mail.

TFX has a Rotary model. My version is an older model but they support it well.


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).

Correct, I need two more sensors to read full cycle. One in the exhaust port and on in the intake port (which then can lead to more tests of tuned lengths and overlap pressures).

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

Barry

[Barry Bordes]

Thanks Barry,

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

My contact at TFX Engine Technology is Clint Gray.

Their website has a better explanation of all the functions. http://www.tfxengine.com/index.html

Their system goes for about 5k. The plug was $1300.

All technical input is appreciated,

Barry

[TitaniumTT]

Do we really need to turn this into a playground spat?
Can we drop the name calling?

This thread is GOLD.
Anyone who understands the data being presented knows that this kinda stuff is PRICELESS.
I think this is the first time I've seen such data on ANY RX-7 type of forum.
I've only read about stuff like this is SAE papers.
To have a member actually messing around with such equipment is just unheard of.

It would be sad if this thread gets closed.


-Ted

Agreed.... 100% agreed

Vex Ted and Classicauto.
Not using two plus per rotor would definitely invalidate the findings.

My third iteration spark plug is a –10 heat range TFX model, with a platinum electrode.
The only negative effect that it might have on combustion is that it is ¾” vs the Rotary designed reach of 7/8”.

Things to be tested are: with and without water, water/meth, splits, negative splits in vacuum, advance curves, port shapes, you name it.
Barry

That is just awesome

[NoDOHC]

Sorry about the confusion, I thought the same thing that others did, this was a simple transducer installed in the leading spark plug hole.

From what I have seen, there is more available power by building that peak pressure earlier in the cycle. If you are seeing detonation with earlier pressure peaks, 45 degrees is what you get. (This really isn't too bad, at is equates to 30 degrees on a piston engine. As I recall, 12-15 degrees is the sweet spot for peak cycle efficiency (on a piston engine). The rotary may be different.

Actually, now that I think about it, the rotary has a longer combustion chamber and probably requires longer for the flame to propagate. This may mean that the pressure will spike too quickly is it is initiated any sooner, while taking too long to propagate if initiated at this time.

Anyway, I hope that you are planning to analyze the effects of leading/trailing split. Some claim that it makes a big difference, I found no change on the dyno at all for pretty much the entire test.

In fact, I unplugged the trailing plugs and saw no change under 6,000 rpm.

[vex]

Barry do you know your %error on the calculations at all?

[Barry Bordes]

Sorry about the confusion, I thought the same thing that others did, this was a simple transducer installed in the leading spark plug hole.

From what I have seen, there is more available power by building that peak pressure earlier in the cycle. If you are seeing detonation with earlier pressure peaks, 45 degrees is what you get. (This really isn't too bad, at is equates to 30 degrees on a piston engine. As I recall, 12-15 degrees is the sweet spot for peak cycle efficiency (on a piston engine). The rotary may be different.

Actually, now that I think about it, the rotary has a longer combustion chamber and probably requires longer for the flame to propagate. This may mean that the pressure will spike too quickly is it is initiated any sooner, while taking too long to propagate if initiated at this time.

Anyway, I hope that you are planning to analyze the effects of leading/trailing split. Some claim that it makes a big difference, I found no change on the dyno at all for pretty much the entire test.

In fact, I unplugged the trailing plugs and saw no change under 6,000 rpm.

NoDOHC, I think flame speed should be our main focus (actually exhaust reversion is the area we can make the most gains).

There are a lot of concepts to interrelate when considering what is going on inside of a rotary engine.

This is from a Mazda paper Rotary86v6a4, Fig. 14, showing flame propagation.

I think this is probably Mazda Research at its best!

If you haven't seen it before please take your time trying to understand it.


http://i287.photobucket.com/albums/ll129/bbordes/flametravel-1.jpg

Some things to note:

Because the mixture is flowing the flame front hardly moves upstream at all. In fact the trailing portions of both flame patches are pushed backwards part of the time.

The squish generation and trench shape further complicates this movement.

When the leading and trailing flame fronts collide (at about 20º ATDC) that their speed diminishes.

The knock region is from 30º - 45º ATDC and where the knock sensor is located.

Barry

[Barry Bordes]

Barry do you know your %error on the calculations at all?

The sensor specs are ±1% for Combustion.
The timing trigger that I fabricated adjacent to Mazda’s timing wheel would be the area for greatest possible error.

To check this a test run is then made where the engine ignition is cut at 6000 rpm and the throttle is opened fully. This double-checks TDC in relation to the logged actual compression hump.

To my knowledge the rest are calculations.

http://i287.photobucket.com/albums/ll129/bbordes/IMG_8427.jpg

[NoDOHC]

Correct me if I am completely mistaken, I will try to explain the figure.

The diagonal lines indicate the position of each component as the rotor rotates.

The angle indications are in rotor degrees, not eccentric shaft degrees.

The distance from the left indicates degrees of rotation when that region of the chamber burned.

The different lines are the different ignition timing settings that clearly cause significantly different behavior.

The trailing side seems to be the weird one, the flame front displacement seems to shift nicely for all points below the leading plug.

It looks like the flame front is traveling forward just fine, it is the backward part of the curve that confuses me. This would seem to indicate the the flame front follows the rotor rather than the housing (which makes sense, the rotor has the dish).

I think I see why it knocks right above the trailing plug, the flame front actually reverses direction there (although not relative to the rotor). This must be right at the quench boundary at the edge of the rotor dish (probably when it meets the cusp on the housing).

Do you know what the engine speed was for this test? Do you know the manifold pressure? (I would guess NA).

It appears that at 20 BTDC, the leading front has basically dissipated by 45 degrees (Eccentric shaft, 15 rotor) (which makes sense why you observed the highest pressures when the peak occured at 45 degrees)

Here is a theory about what is causing your knock on too much timing advance. Knock is typically caused by some shock wave colliding with the flame front (it can be a second flame front). My thought is that the leading and trailing sparks both touch off the mix in the chamber if the timing is advanced too far, this results in the two flame fronts colliding while they are stil moving very quickly. To test this, you could try unplugging the trailing plugs or adjusting the ignition split and observing what difference it makes.

This research is awesome. Where did you find that diagram?

[Barry Bordes]

Correct me if I am completely mistaken, I will try to explain the figure.

The diagonal lines indicate the position of each component as the rotor rotates.

The angle indications are in rotor degrees, not eccentric shaft degrees.
I believe they are in shaft degrees.

The distance from the left indicates degrees of rotation when that region of the chamber burned.

The different lines are the different ignition timing settings that clearly cause significantly different behavior.
X is observed through a quartz window, O is taken from an ion plug, and the other two are calculated.

The trailing side (due to squish influence ) seems to be the weird one, the flame front displacement seems to shift nicely for all points below the leading plug.

It looks like the flame front is traveling forward just fine, it is the backward part of the curve that confuses me. This would seem to indicate the the flame front follows the rotor rather than the housing (which makes sense, the rotor has the dish).
We should think of the mixture flowing like a river and ignition spacing like dropping two rocks into it. Each wave travels downstream easily, upstream not so well. But what happens when the two waves collide? This interaction slows the flame speed (notice the dogleg in the LL at the bottom of the graph).

I think I see why it knocks right above the trailing plug, the flame front actually reverses direction there (although not relative to the rotor). This must be right at the quench boundary at the edge of the rotor dish (probably when it meets the cusp on the housing).

Do you know what the engine speed was for this test? Do you know the manifold pressure? (I would guess NA).
The X Measurments were done through Quarts windows NA at 1000rpm.

It appears that at 20 BTDC (ATDC?) , the leading front has basically dissipated by 45 degrees (Eccentric shaft, 15 rotor) (which makes sense why you observed the highest pressures when the peak occured at 45 degrees)


Here is a theory about what is causing your knock on too much timing advance. Knock is typically caused by some shock wave colliding with the flame front (it can be a second flame front). My thought is that the leading and trailing sparks both touch off the mix in the chamber if the timing is advanced too far, this results in the two flame fronts colliding while they are stil moving very quickly. To test this, you could try unplugging the trailing plugs or adjusting the ignition split and observing what difference it makes.

This research is awesome. Where did you find that diagram?
This is from a Mazda paper Rotary86v6a4, Fig. 14, showing flame propagation.

NoDOHC, thanks for the input.
Barry

[NoDOHC]

Shaft degrees makes more sense in the diagram (the rotor would have moved quit a bit further at 90 degrees). I think I was second guessing myself.

The reason I consider the ignition event to be at 20 BTDC is that there is observeable flame front propagation before 0 degrees, which excludes the ATDC option. It is strange that they neglect to indicate ATDC or BTDC.

I saw the reference earlier, I meant where did you find the paper? Is that an SAE paper?

This explains what I saw in several articles about trailing plug positioning, that further up the housing (rotor clears it earlier) is preferred for peak power.

edit: It would be really awesome to see what the flame front does at 7,000 rpm....

[vex]

The sensor specs are ±1% for Combustion.
The timing trigger that I fabricated adjacent to Mazda’s timing wheel would be the area for greatest possible error.

To check this a test run is then made where the engine ignition is cut at 6000 rpm and the throttle is opened fully. This double-checks TDC in relation to the logged actual compression hump.

To my knowledge the rest are calculations.



By sensor specs for combustion do you mean the transducers? Out of curiousity how did you calibrate your transducers? Did they calibrate them for you and ship them with a cert of it (sorry for the questions, it's the engineer in me again--we've been repeatedly told "never trust some one elses calibration unless you absolutely have to"). Would I be correct in assuming the sensors are linear in nature until a certain point, or are they non-linear from min-read to max? (out of curiosity do you know what the resolution of your timing sensor is? ie: can it read only 1 degree or can it read minutes, or seconds?)

If you know the calculations they're running for any given reading you can easily perturb the uncertainties to get a culmulative percentage of error. That way you can at least know the accuracy of your results. From my glances you could be on the mark or you could be slightly off. Without the error it's hard to gage application to different stress/repeatabilty.

[Barry Bordes]

By sensor specs for combustion do you mean the transducers? Out of curiousity how did you calibrate your transducers? Did they calibrate them for you and ship them with a cert of it (sorry for the questions, it's the engineer in me again--we've been repeatedly told "never trust some one elses calibration unless you absolutely have to"). Would I be correct in assuming the sensors are linear (yes linear) in nature until a certain point, or are they non-linear from min-read to max? (out of curiosity do you know what the resolution of your timing sensor is? ie: can it read only 1 degree or can it read minutes, or seconds?)

You realize at 360º X 8000 rpm it is taking at almost 3 million samples /min. My laptop is the restriction right now and I would like to add 2 more sensors ( for intake and exhaust ports).

If you know the calculations they're running for any given reading you can easily perturb the uncertainties to get a culmulative percentage of error. That way you can at least know the accuracy of your results. From my glances you could be on the mark or you could be slightly off. Without the error it's hard to gage application to different stress/repeatabilty.

Vex, check out this info, (Very accurate and cost effective, an interesting combination).

For aircraft testing instrumentation we had to recertify sometimes every six months. I don't want to certify different dynos for the FAA or DOT. I want it to be accurate but I will pass on recertification.

Really I just want to know is this log an improvement or have I gone too far!
I am using it just like our Datalogit tuning for AFR, transition, etc.

http://www.optrand.com/Papers/fisita98/fisita98.htm

Barry

[vex]

Oh believe me I know about samples and windowing. It's annoying as crap ;) Hence why I asked the question.

As for the 3 million/min... why do you make me do math? I hate math! so you'd be sampling at 48khz unless you wish to avoid windowing then you'd need to sample at 96khz. Is the timing sensor hall or optical? (I'm trying to estimate the sensor error to guesstimate the perturbed error)

so your calibration uncertainty is 0.04% which ain't bad. If you can nail down the timing uncertainty it will be easy enough to get an uncertainty plot for the pressure distribution.

[Barry Bordes]

Oh believe me I know about samples and windowing. It's annoying as crap ;) Hence why I asked the question.

You are over my head with windowing functions.

As for the 3 million/min... why do you make me do math? I hate math! so you'd be sampling at 48khz unless you wish to avoid windowing then you'd need to sample at 96khz. Is the timing sensor hall or optical? (I'm trying to estimate the sensor error to guesstimate the perturbed error)

The system, I think is 80Khz, and it uses an optical pickup.

so your calibration uncertainty is 0.04% which ain't bad. If you can nail down the timing uncertainty it will be easy enough to get an uncertainty plot for the pressure distribution.

Barry

[vex]

Barry

Windowing occurs when you sample something too slowly and the result is a different reading altogether. For instance say you take a sample of a simple sine wave with a frequency (i'll keep it simple) of 4khz. If you sample that same sine wave at some other frequency that is less than 4khz you could get some surprizing results. Windowing would occur and you may end up looking at a cosine wave with a frequency of 2.3khz and a different amplitude that fluctuates over time. Not exactly what you're looking at? For DAQ's it is a good rule of thumb to sample at twice the frequency than what your expecting to be as your function. IE: if you are ever going to see 48khz in a function you'd want to sample double that to ensure you don't have window the function.

There is also another windowing occurance which usually helps in DAQ systems and is fairly easily explained in the following wiki article:
http://en.wikipedia.org/wiki/Window_function

[Barry Bordes]

Windowing occurs when you sample something too slowly and the result is a different reading altogether. For instance say you take a sample of a simple sine wave with a frequency (i'll keep it simple) of 4khz. If you sample that same sine wave at some other frequency that is less than 4khz you could get some surprizing results. Windowing would occur and you may end up looking at a cosine wave with a frequency of 2.3khz and a different amplitude that fluctuates over time. Not exactly what you're looking at? For DAQ's it is a good rule of thumb to sample at twice the frequency than what your expecting to be as your function. IE: if you are ever going to see 48khz in a function you'd want to sample double that to ensure you don't have window the function.

There is also another windowing occurance which usually helps in DAQ systems and is fairly easily explained in the following wiki article:
http://en.wikipedia.org/wiki/Window_function

Vex,

I believe the program will throw an error code when the data is not acceptable.

Barry

[scotty305]

For DAQ's it is a good rule of thumb to sample at twice the frequency than what your expecting to be as your function. IE: if you are ever going to see 48khz in a function you'd want to sample double that to ensure you don't have window the function.


I don't mean to be contrary, but I received the same 'sample at double the input signal frequency' advice from textbooks and some professors. Other professors with more real-world industry experience advised that data will be much more useful when sampled at no less than 5-10x the signal frequency. Try sampling a 100Hz sine wave at 200Hz, the plotting the results... it's not going to look much like a sine wave. If you logged a fuel injector its operating frequency, the indicated duty cycles would always be 0%, 50% or 100%... Personally I'd like to at least know +/-10%.


80kHz sounds like a very reasonable sampling rate. Assuming the sensor responds quickly enough, an 80k sample rate will give you one datapoint every ~0.5 eccentric shaft degrees at 6500 RPM.

Compare this to the RX-7 'crankshaft' position sensor which has one tooth every 30 degrees... I wonder if your ECU's ignition timing accuracy is better or worse than +/- 0.5 degrees? If your logger has a spare input it would be very interesting to monitor the ignition trigger signals in addition to chamber pressure, either by tapping into the 0/5V signal going from the ECU to the ignitor or by tapping the wire between the ignition coil and ignitor (careful, this will be over +20V due to inductive flyback... make sure the logger can handle it).

[vex]

I don't mean to be contrary, but I received the same 'sample at double the input signal frequency' advice from textbooks and some professors. Other professors with more real-world industry experience advised that data will be much more useful when sampled at no less than 5-10x the signal frequency. Try sampling a 100Hz sine wave at 200Hz, the plotting the results... it's not going to look much like a sine wave. If you logged a fuel injector its operating frequency, the indicated duty cycles would always be 0%, 50% or 100%... Personally I'd like to at least know +/-10%.
You're right. I forgot the word 'least' after at.

[Barry Bordes]

This is the way we can get more area under the curve. Notice that the end that changes most is the leading peak pressure end. If you could view each firing of the rotor it would look similar to the five curves shown with not much movement of the trailing tail.

http://i287.photobucket.com/albums/ll129/bbordes/combustionlate.jpg

[Barry Bordes]

Good news and bad news.

As the mean effective pressure has increased through changes in timing a new problem has arisen. Preignition!

The in-chamber testing can show us the beginning of combustion pressure from the small ignited kernel of flame front, but it is so small at first that the pressure change usually only shows an increase after about 5º of eccentric movement (15º BTDC advance starts showing pressure at 10º BTDC). Imagine our surprise when we started seeing a pressure rise starting at 28º BTDC!

The crazy thing is that it made more power and no real detonation!

Barry

http://i287.photobucket.com/albums/ll129/bbordes/preignition.jpg

[NoDOHC]

The curve is ugly, but I like the timing! You should be about peak power at this point (12-18 degrees ATDC for peak pressure).

Keep up the good work! (Try not to hurt your engine, I don't know how safe it is to run a turbo at optimal ignition timing. Most turbo cars I have seen run REALLY retarded.

[Barry Bordes]

The curve is ugly, but I like the timing! You should be about peak power at this point (12-18 degrees ATDC for peak pressure).

Keep up the good work! (Try not to hurt your engine, I don't know how safe it is to run a turbo at optimal ignition timing. Most turbo cars I have seen run REALLY retarded.

Notice that this is not the pressure chart but the burn rate. It is ugly but fairly typical. There seems to be a wave cycle of burning.

The proper term for what is happening is probably auto-ignition.

I think Honda has the answer with their two stroke experiments into Active Radical Combustion.

“When the spark plug fires and ignites the fuel mixture, some of the fuel is isolated from the resulting flame by the exhaust still in the cylinder, and does not burn. What Honda has done is to develop a way to ignite all the fuel in the cylinder by using the properties of auto-ignition, and has termed this process Activated Radical Combustion. This title is derived from the way fuel actually ignites. When the fuel is brought to the right pressure and temperature, the molecules break down into what are known as active radical molecules. These are highly unstable chemical compounds which are an intermediate step in the actual combustion reaction. When hot exhaust gas remains in the cylinder, it contains a small percentage of active radical molecules; when these are combined with the incoming fuel charge, the resulting mixture begins to auto-ignite at lower temperature that a pure gasoline/air mixture. What we currently associate with auto-ignition is engine knock, a phenomenon that occurs when the fuel ignites before the spark plug fires, while the piston is still on the up-stroke”

I am working with a Gorilla (Jonathan) and a Trout2 (Jack) on this project.

The real question may be… do we try to eliminate the reversion causing auto ignition or try to control this new ignition source with some type of valve?

Thanks for your input, we learn together,
Barry

[NoDOHC]

I thought that the hand-drawn pressure curves above corresponded to the burn curve below. I didn't intend to add confusion

Could you show the pressure curve for burn initiation @ 28 BTDC?

[Barry Bordes]

http://i287.photobucket.com/albums/ll129/bbordes/preignitionpressurecurve.jpg

Notice the light-off hump at 30º BTDC, also later when the exhaust port opens it has still has 132 psi and 1750ºC temp.

Barry

[NoDOHC]

Peak pressure still at 38 degrees, if that engine were NA, I recommend that you advance the timing more. Turbo, you probably have it pretty much maxed out.

Are you sure that the exhaust port opening time on the chart is accurate? I would have expected the pressure to drop significantly more than 12 psi in 15 degrees of eccentric shaft rotation if the exhaust port were open. This is very close to the curve that would be followed with the port closed. I know that the exhaust port opens 75 degrees before BBDC = 195 ATDC, but I suspect that the trace may be inaccurate in scaling (which is weird, because the no-fire trace line looks Ok).

Can you continue the trace out to 250 ATDC? Your sensor should be able to read about that long.

[Barry Bordes]

Peak pressure still at 38 degrees, if that engine were NA, I recommend that you advance the timing more. Turbo, you probably have it pretty much maxed out.
Actually 851psi @ 40ATDC

Are you sure that the exhaust port opening time on the chart is accurate? I would have expected the pressure to drop significantly more than 12 psi in 15 degrees of eccentric shaft rotation if the exhaust port were open. This is very close to the curve that would be followed with the port closed. I know that the exhaust port opens 75 degrees before BBDC = 195 ATDC, but I suspect that the trace may be inaccurate in scaling (which is weird, because the no-fire trace line looks Ok).
The 5000 psi sensor's error of 1% would be 50 psi. It is probably having a difficult time with resolution down there. The exhaust port opening is written into the engine spec for the program. I estimated it at 196º ATDC. The pressure still has work to do driving the turbine wheel, it probably would show a more distinct drop off if NA. We probably need another sensor on that side of the housing (hopefully in the future one each in the exhaust and intake ports).


Can you continue the trace out to 250 ATDC? Your sensor should be able to read about that long.
No that is the standard span for the program's chart.

Barry

[NoDOHC]

The 5000 psi sensor's error of 1% would be 50 psi. It is probably having a difficult time with resolution down there. The exhaust port opening is written into the engine spec for the program. I estimated it at 196º ATDC. The pressure still has work to do driving the turbine wheel, it probably would show a more distinct drop off if NA. We probably need another sensor on that side of the housing (hopefully in the future one each in the exhaust and intake ports).

You could be right. I am not used to looking at pressure curves for gasoline-fueled turbo engines. The valve opening on a piston engine is visible in the trace, even with their slow valve loft. Valve open actually looks a lot like the shift in the curve at 175 ATDC.

[Libor]

Bump this up.

Barry, are you going to do some tests with tighter or zero split?

Also I think there is slight misconception when should peak pressure occur. IIRC at 45° ATDC, rotor has most mechanical leverage over e-shaft, but peak pressure for optimal efficiency should occur much earlier.

Otherwise best of luck with your testing

[Barry Bordes]

Bump this up.

Barry, are you going to do some tests with tighter or zero split?

Also I think there is slight misconception when should peak pressure occur. IIRC at 45° ATDC, rotor has most mechanical leverage over e-shaft, but peak pressure for optimal efficiency should occur much earlier.

Otherwise best of luck with your testing

Libor and DOHC,
You know how the rotor moves at 3:1 ratio to that of the eccentric shaft. That seems to be the sweet spot for the rotary, that is, 15º times 3 or 45º. This latest run with the new sensor has gone to 1000 psi for the first time. But the highest pressures seem to be around 45º. I think I am seeing a slight deviation in this with rpm.

But I have exactly the same thoughts as you. Looking at the chart, if we could have the ignition pressure rise as a continuation of the initial compression curve it would seem to be logical.

Barry




http://i287.photobucket.com/albums/ll129/bbordes/1k47atdc.jpg

[Libor]

But I have exactly the same thoughts as you. Looking at the chart, if we could have the ignition pressure rise as a continuation of the initial compression curve it would seem to be logical.

Barry

Exactly. I´ve been lately looking at these charts - granted, they come from piston engines but principal is the same. Pressure rise seems very delayed. And burn rate is so much different from piston engines, also takes much more time.

But as I said, carry on your testing! Nothing is better than actuall data:302:

[Barry Bordes]

http://i287.photobucket.com/albums/ll129/bbordes/pressurelocation-3.jpg

This chart actually predicts the sweet spot.

You have to look closly to see the location where pressure is highest. Too bad we don't have more hits around 40º.

Then you go to your ignition adjust the timing.

Barry