In Chamber Testing

[C. Ludwig]

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

[RICE RACING]

Originally Posted by C. Ludwig

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

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 I looked into it a long time ago, still have quotes probably on it.

[C. Ludwig]

Originally Posted by RICE RACING

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 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]

Originally Posted by C. Ludwig

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.

[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.

[Barry Bordes]

Originally Posted by 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.

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.




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

[vex]

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

[Barry Bordes]

Originally Posted by vex

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.

[vex]

Originally Posted by Barry Bordes

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]

Originally Posted by vex

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

[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]

Originally Posted by 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.
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]

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]

Originally Posted by vex

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