Combustion Pressure sensors

[Mark944turbo]

Is there a website out there that actually lists these things for sale? Preferably with prices?

I am looking into these as an aid in my engine building/dyno service business.

Any help or info is appretiated. I know they are expensive.

Thanks

 

[CESSNA1]

MARK944TURBO: Try this site. These sensors involve drilling into the combustion chamber chamber somewhere. I encountered this issue some years ago and the problem was not pressure sensors, but temparture sensors. Most temperature sensors do not react fast enough. You either bought temp sensors or estimated it from the gas laws.

http://www.optrand.com

Good Luck
Dave

 

[GregLocock]

Kistler make them. We've got a few instrumented spark plugs, they are handy.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[bobqzzi04]

I am in the process of buying a complete set-up from

http://www.tfxengine.com/

They offer both the kistler piezeo-elecric sensors and the optrand fiber optic sensor (both are available as sparkplug mounted or chamber mounted) and have appropraite software for both.

 

[Mark944turbo]

Thanks for the replies. Bob, can you give me a ballpark on what price you are paying and for what things you are getting? I have sent them an email, but I thought I would ask here too in case I get a faster response.

I really like the user interface of the tfx logging software.

 

[Warpspeed]

Reading through the specifications of both devices, it seems the Optrand gives a direct voltage output with pressure. The Kistler on the other hand requires a special charge amplifier with correctly calibrated gain.

I have not used either, but am looking for a low cost system myself. When comparing the cost of the actual sensors, do not forget to include any special signal processing electronics that may also be required to drive your data acquisition system.

 

[ale58]

both Kistler and AVL make this kind of sensor working with charge amplifiers.
If you are interested in gas exchange analisys check for low pressure precision.

 

[tbuelna]

Mark944turbo,

Since you mention that you have a dyno service, I would assume you do not wish to be drilling holes in the cylinder heads of your customer's engines, simply to install cylinder pressure transducers. Thus, you probably want something that fits into the existing spark plug hole for SI engines, or something that fits into the glow plug hole for CI engines. And of course, something that is compatible with your data acquisistion system. Combustion pressure measurements require a very high sampling rate.

Check out Kistler, AVL and Beru:

http://www.beru.com/english/aktuelles/presse/20040629.php

http://tec.avl.com/wo/webobsession.servlet.go?app=kbase&page=content-management/view&id=400013055

http://www.kistler.com/web/portal.nsf/urlnames/App100_en?OpenDocument&CTY=US&L=en

I only have limited experience with cylinder pressure transducers, but they were expensive and very easy to damage by overheating (even the water cooled ones!). Another issue for me (not being an instrumentation expert) was I never really knew if I was getting a correct calibration.

Regards,
Terry

 

[Warpspeed]

Terry, a very simple home made dead weight tester would solve your calibration issues.

Basically you screw the sensor to be tested into the base of a small vertical test cylinder with accurate known bore diameter. Then place some light oil into the cylinder.

A closely fitting piston is then inserted with a disc shape weight attached to the top of the piston rod. If total weight of piston and disk is known, and bore diameter is known, the test pressure can be easily calculated.

To remove any sliding friction from the piston, the piston and disc shaped weight can be made to slowly revolve by hand. It will continue to rotate by itself for quite a long period just through inertia, and the developed pressure will be exact.

A thing device like this is very easy to construct, and a range of weights can be provided to check the pressure calibration of all sorts of gauges and transducers.

Nationally accredited standards labs use dead weight pressure references as pressure standards. A real laboratory one would be ferociously expensive. But a home made job should be well within the capability of most of us here. They are extremely accurate and repeatable.

 

[GregLocock]

Um, no. A static calibration tells you nothing about the dynamic performance. Typically the problem with a sparkplug transducer is that the pressure sensor is at the end of a long, narrow passage. A very good question is - what is the relationship beteen the instantanous pressure measured by the transducer, and the actual average pressure in the chamber? And what is the frequency response?

Until you can answer those questions properly then you are sailing blind.



Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[Mark944turbo]

The cheapest setup from TFX comes to about 4 grand including sensors and logging equipment, which is in my budget. I definately want the spark plug mounted model.

I am going to bring up these points about accuracy, calibration, overheating, etc with the company, and see what they have to say.

Please continue pointing out expected issues, it helps me a lot.

 

[Warpspeed]

Greg, what you say about the required high frequency response is very true, but that is an inherent feature of the original transducer design.

Usually pressure transducers (or gauges for that matter) that have been abused, suffer from a marked change in full scale sensitivity, or a significant shift in the zero pressure output. It is difficult to conceive of how a transducer can suddenly lose all it's high frequency response while still remaining within its specified static accuracy.

A static pressure calibration test does, in my experience confirm that the sensor is still working to its full original specification. Any internal transducer damage always shows up in a static test.

I definitely agree with you on the importance of the acoustic coupling properties of any long interconnecting passage. That might certainly modify the observed pressure waveform. That is particularly true of the sorts of waveforms that typically indicate combustion problems. Reflections and resonances in a long passage are definitely not going to help the fidelity of the measured pressure waveform.