Chamber Pressure Monitor

[Fingers]

Found the Specs for the sensor.

30 times less responsive than what is in my kit, but it might be enough.

They have a gasket near the end of the glow plug to seal the internal conduction rod. I use a conduction rod too, but I had no luck keeping the seal from burning out that close to the chamber when the chamber got hot. My seal is closer to the sensor itself.

Then again, this is meant to keep the pressures and heat in check in the chamber, so I can see it working perfectly for it's intended application.

 

[Fingers]

Here is a link to Beru's description/specs.

The animation is scary close to how mine are made.

 

[duratothemax]

only maxes out at like 3000psi?

 

[McRat]

If that's right, at 3300rpm, it can only sample at about 4° crank rotation intervals.

I was sampling at 1 deg or less when I was dinking with my sensor. I don't think 4° will be enough.

 

[Fingers]

Sampling rate and freq response a different. Sampling rate is what your DAQ does. How many times it looks at the sensor for instance. Freq response is roughly how fast the sensor reacts. Or put another way, how quick an event it can track accurately.

All sensors have latency in them. The one I use for instance can go from zero to full scale in ~1 micro-second. This one looks to be about 200 micro-seconds. At 4000 RPM, each degree takes about 40 micro-seconds. However, the area of interest where the pressure sweeps up and challenges the sensor's response takes about 3000 micro-seconds. (90 degrees before TDC)

What that all means is this sensor ain't bad, but will start to come up short (inaccurate) as you rev over ~3000 RPM. By 4000, the data is suspect. Still useful for the application it was intended though. Bottom line, it is not a good replacement for what is currently being used IMO.

 

[Diesel power]

Sampling rate and freq response a different. Sampling rate is what your DAQ does. How many times it looks at the sensor for instance. Freq response is roughly how fast the sensor reacts. Or put another way, how quick an event it can track accurately.

All sensors have latency in them. The one I use for instance can go from zero to full scale in ~1 micro-second. This one looks to be about 200 micro-seconds. At 4000 RPM, each degree takes about 40 micro-seconds. However, the area of interest where the pressure sweeps up and challenges the sensor's response takes about 3000 micro-seconds. (90 degrees before TDC)

What that all means is this sensor ain't bad, but will start to come up short (inaccurate) as you rev over ~3000 RPM. By 4000, the data is suspect. Still useful for the application it was intended though. Bottom line, it is not a good replacement for what is currently being used IMO.

so will your kit work with say 6-7 k RPM?

 

[duratothemax]

What that all means is this sensor ain't bad, but will start to come up short (inaccurate) as you rev over ~3000 RPM. By 4000, the data is suspect. Still useful for the application it was intended though. Bottom line, it is not a good replacement for what is currently being used IMO.

but arent our areas of cyl. pressure tuning done below 3,000 rpm anyways? ie, how to control cylinder pressures in the ~2000rpm range to protect rods and pistons?

 

[Roc8man]

I've been very interested in this for quite some time but I have yet to be satisfied that the data is accurate given what information I have. If it isn't accurate, then it's not worth much to me regardless of how fast you can get it. The other question that comes to mind is what to do with the data assuming it is accurate. Where do we draw the line as far as max cylinder pressure? Is there a known value that will cause rods to break or head gaskets to blow? Without that, having the data doesn't provide anything other than entertainment until you do blow something up and then it is too late. Anyone want to volunteer to see what that is?

David

 

[Fingers]

so will your kit work with say 6-7 k RPM?

The Sensor should be fine at those RPM with the 1 uS rise time. The DAQ portion samples at 50KS/s which turns out to be about a sample a degree at 8000 RPM.

I have not tested anything near that yet though. There are a couple things that can start to become a factor at higher RPM. I have tried to address many of them already, but I can't claim success till someone actual challenges the equipment.

 

[Fingers]

but arent our areas of cyl. pressure tuning done below 3,000 rpm anyways? ie, how to control cylinder pressures in the ~2000rpm range to protect rods and pistons?

You would be surprised what you see at high revs....

 

[Diesel power]

The Sensor should be fine at those RPM with the 1 uS rise time. The DAQ portion samples at 50KS/s which turns out to be about a sample a degree at 8000 RPM.

I have not tested anything near that yet though. There are a couple things that can start to become a factor at higher RPM. I have tried to address many of them already, but I can't claim success till someone actual challenges the equipment.

sounds great! im interested for sure, PM me the cost please.

 

[Diesel power]

You would be surprised what you see at high revs....

Elaborate....

 

[Fingers]

I've been very interested in this for quite some time but I have yet to be satisfied that the data is accurate given what information I have. If it isn't accurate, then it's not worth much to me regardless of how fast you can get it. The other question that comes to mind is what to do with the data assuming it is accurate. Where do we draw the line as far as max cylinder pressure? Is there a known value that will cause rods to break or head gaskets to blow? Without that, having the data doesn't provide anything other than entertainment until you do blow something up and then it is too late. Anyone want to volunteer to see what that is?

David

For all you penchant for accuracy, the failure line for any component is not going to be some fine line that if you cross you break and if you don't you are "safe". Never will be.

But to address accuracy a little. The sensors come with certificates as do the DAQs. All told you get within about 100 PSI, (+/- 1%) but of a dynamic number. That is, what was the pressure change from low to high. You never get a PSI in absolute or gauge reference. It is the nature of being able to measure and plot such rapid events.

However, the repeatability is +/- 20 PSI or better.

On another note, the use of this tool is not just peak pressure, it is the shape of the pressure curve. Not unlike a Dyno plot, you have to read and interpret the data. From the plot you can tell, with practice, when you should add or take away timing. Also, with practice, you can see when you are getting an overly hot chamber.

Cool stuff. At least I think so.

 

[Fingers]

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...

 

[Fingers]

Elaborate....

Heat loading of the chamber. Unburnt fuel raising the pressure just before the exhaust valve opens. Valve float.

But man do you have to ponder a lot of graphs. You have to get a feel for what is normal and good first so you can pick out an odd whatever.

 

[duratothemax]

but what do I know...

nothing



but in all seriousness Jon...Im bummed we didnt hook up your widget to my truck at merchants. Could have seen what sort of cyl pressures those badazz rods were being subjected to. (I had not changed the tune since merchants to when they broke/bent)

 

[NemesisDP]

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.

 

[Fingers]

There are other systems out there. But they are not even close to this price.

FWIW, I don't personally care if any one else buys one of these. They are a tool that I think would benefit the diesel community at large
.

 

[Diesel power]

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...

Would this be a max Psi in even a performance built engine with much better rods and piston.......or just a stock situation?

 

[Fingers]

Would this be a max Psi in even a performance built engine with much better rods and piston.......or just a stock situation?

Originally Posted by Fingers
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...