Chamber Pressure Monitor

[McRat]

A buddy of mine says that ATS has been doing this for a while and been testing it on the 7.1 stroker. Maybe Guy can chime in. Don't know the truth to this though. The way clints truck ran at Truck fest I would guess thats one of them. Reved VERY fast.

There were rumors of shops doing cylinder pressure testing dating back to 2004. But none of them could produce a graph of a diesel engine at idle. One even posted a sportbike dyno graph to back up their claim, copied off a website.

Until Fingers came out with his system, the only systems you could buy "plug and play" were in the $50,000 price range.

 

[Roc8man]

Oh, about stock rod bending pressures. Stay below 3000 PSI and you should be OK. Pressures up to about 3500 PSI are tolerable as long as your peak pressure is not happening too close to TDC. If and when you close in on 4000 PSI, you will know it both from the engine sound and the eventual parts failure.

but what do I know...

So are the pressures you are quoting above absolute, gage or just a change in pressure in psig? I understand that there is no "magic number" for stepping over and causing castrophic failure, but when the sensor says you're running A LOT more pressure than what calc's out by diesel researchers under no load and running downhill without injection, it makes me wonder if the data is off regardless of a certificate of calibration which brings me to the next question. How can there be a certificate of calibration if the data being read isn't absolute or gage pressure and can be compared to a known gage or absolute pressure or even gage pressure change? Believe me, I really want to get one of these from you because I believe the price is a screamin deal but I have to know that the data is real and that includes the shape of the graph. I hope you understand I'm not trying to bash it but want to understand it before I spend any money on it.

Another question I have is when you posted the data graphs previously, it showed around 3400 psi for the peak pressure. Was that on an engine with stock rods? You also posted a graph that showed a peak of 3600 psi with a big pulse, did that engine have stock rods also and what was the boost?

Thanks again and I hope to do business with you.

David

 

[McRat]

It's my belief that the system has to get in the hands of more hotrodders so that sense can be made of the data.

It is no far stretch that this can be used to control max engine output to "save" engines, but first we have to define what safe is, and what it's not. You could even feed the info into EFILive through DSP2/5 or other means to actively control cyl pressures in sort of a "closed loop" fashion. This is what Volkswagen is doing.

 

[Fingers]

So are the pressures you are quoting above absolute, gage or just a change in pressure in psig?

Pressure change.

I understand that there is no "magic number" for stepping over and causing castrophic failure, but when the sensor says you're running A LOT more pressure than what calc's out by diesel researchers under no load and running downhill without injection, it makes me wonder if the data is off regardless of a certificate of calibration which brings me to the next question. How can there be a certificate of calibration if the data being read isn't absolute or gage pressure and can be compared to a known gage or absolute pressure or even gage pressure change?

Dynamic calibration at the factory. That is, change the pressure a known amount, and check that the sensor tracks the change.

I think we had the conversation about comparisons to theory via PM? Cold chamber, the values track well with theory as I recall. However, unless you have a good number to use to for the thermal energy that is added to the air charge via a hot chamber, I don't think you will be able to predict the pressures.

Believe me, I really want to get one of these from you because I believe the price is a screamin deal but I have to know that the data is real and that includes the shape of the graph. I hope you understand I'm not trying to bash it but want to understand it before I spend any money on it.

I suggest you don't spend your money. There are more factors than I have answers for. You have to be willing to find those factors that influence the data instead of blaming the equipment. It will not come from the simple Boyles Law equations. Those are only a starting point.

Another question I have is when you posted the data graphs previously, it showed around 3400 psi for the peak pressure. Was that on an engine with stock rods? You also posted a graph that showed a peak of 3600 psi with a big pulse, did that engine have stock rods also and what was the boost?

I would have to dig up the other related data. If it was typical, it would have been 25-30 PSI boost on a stock motor. Ive used the information to adjust the tune to keep the peak pressures in the lower end of 3000-3500. Even so, The engine may have been hurt.

Thanks again and I hope to do business with you.

David

Let others play with this David. You are too intent on predicting the data instead of collecting it.

 

[Fingers]

VW is using the pressure sensor to save emissions by controlling peak pressures and thus NOx production.

But what do I know.

 

[duratothemax]

VW is using the pressure sensor to save emissions by controlling peak pressures and thus NOx production.

x2. VW isnt running the engine anywhere near failure point. I highly highly doubt they are relying on their new cylinder pressure sensors to prevent bending the rods.............

 

[McRat]

...to actively control cyl pressures in sort of a "closed loop" fashion. This is what Volkswagen is doing

x2. VW isnt running the engine anywhere near failure point. I highly highly doubt they are relying on their new cylinder pressure sensors to prevent bending the rods.............

VW is running closed loop cylinder pressure control. Yup, it's for emissions. Yup, that's what we need to control engine damage instead.

Kinda like you can use O2 sensors or MAF sensors to control emissions or make more power. Tech is the same, use is different.

 

[rgullett83]

Very impressive fingers, your knowledge overwhelms me.

 

[Roc8man]

Let others play with this David. You are too intent on predicting the data instead of collecting it.

The data should be accurate and if it isn't, it isn't worth squat unless people just want numbers that have no real value to them but make them feel good about gathering it. The data you acquired during the simplest form of diesel compression (no injection, coasting downhill, warm engine) should be close to empirically derived equations that are based on years of diesel research by some of the top researchers and when your data doesn't jive with that, something is wrong and it usually isn't the years of empirically derived diesel equations.

By the way, when you say pressure change, it still has to be measured in either psia or psig, which was it?

Good luck,
David

 

[Diesel power]

How high of a pressure can this read, and how many rpm's will it handle before it's off the chart in accuracy.

 

[McRat]

The data should be accurate and if it isn't, it isn't worth squat unless people just want numbers that have no real value to them but make them feel good about gathering it. The data you acquired during the simplest form of diesel compression (no injection, coasting downhill, warm engine) should be close to empirically derived equations that are based on years of diesel research by some of the top researchers and when your data doesn't jive with that, something is wrong and it usually isn't the years of empirically derived diesel equations.

By the way, when you say pressure change, it still has to be measured in either psia or psig, which was it?

Good luck,
David

PSIA or PSIG won't matter within gauge resolution. That's 1/2 a percent difference at 200 bar, which is better than most lab gauges.

Accuracy is not critical in measurement when used a benchmark. If I tell you 55 is too high, 50 is just right, and 45 is too low, you can figure out what 70 and 20 do even if I don't tell you the units involved.

Repeatibility and resolution are important though. If I measure it 3 times, and get 61, 37, 52, I can't tell. That's repeatibility. It's too unpredictable. If it comes in at 50,50,60, I have a problem with resolution. I can't tell where the "edge" is. It only reads to the nearest 10.

 

[Fingers]

The data should be accurate and if it isn't, it isn't worth squat unless people just want numbers that have no real value to them but make them feel good about gathering it. The data you acquired during the simplest form of diesel compression (no injection, coasting downhill, warm engine) should be close to empirically derived equations that are based on years of diesel research by some of the top researchers and when your data doesn't jive with that, something is wrong and it usually isn't the years of empirically derived diesel equations.

So this, nearly adiabatic, plot is just wrong eh? Plot is near the end of a coast down after a dyno run on Dunbar's dyno.

Crude adiabatic calculation for this engine would be 797 PSI. Pressure change should be about 782 assuming no boost. Which is nearly the case here.


By the way, when you say pressure change, it still has to be measured in either psia or psig, which was it?

Good luck,
David

Do you even know what psia and psig mean? The only difference between the two is the Zero reference! For these sensors that reference is not fixed. They can not tell you what a static pressure is, but they can tell you how much it changes.

 

[Fingers]

I had mentioned earlier that you can, with practice, see a hot chamber. I know that the previous plot is showing a nearly adiabatic event. But that happens to be the exception. Nearly always, the air charge is swapping heat with the chamber walls. One way or the other.

The math eludes me right now to pull an estimated wall temperature. But I can assure you in the plot above it would be on the line of 400* F if not higher!

Back in normal chamber temperature land, the pressure cycles are closer to Isothermal. For instance this no load coast down. (crank signal was breaking up and placed TDC in the wrong location, please ignore that detail. :O )

With the cold weather, I have been tempted to see what a truely cold chamber looks like.

 

[Fingers]

Here is a teaser for you.

THIS is a version of the Chamber pressure software. It is self contained save it a run it.

HERE is a dyno run file you can download and play with. Download and unzip the file before you try to load it into the program.

If it doesn't work because of missing DLLs, let me know and I will trim it back to a viewer only version.

 

[minisub]

Hhmmm. That run looks familiar....

Nice to see this topic back in active conversation, this is fascinating stuff. :cool2:

 

[Fingers]

Did it load for you Tom?

 

[8100 Power]

Didn't work for me on Vista. Error: cbw32.dll was missing.

 

[minisub]

Did it load for you Tom?

Honestly, I didn't try - I was on the work machine and they get funny about downloading executables....I knew from the file name what it was.

I'll try here on the home machine when I get in from blowing - got another freakin' 12" today...

 

[Fingers]

Didn't work for me on Vista. Error: cbw32.dll was missing.

I was afraid of that. I'll post the viewer only here as soon as I can a rip the DLL dependencies out.

 

[Fingers]

Here is the viewer only version and here is the zipped data file to play with.

Enjoy!!