Measuring Pressure Pulses

[Ben Wilson]

I've had an idea for a test rig, I'm still trying to work it out.

I'm picturing a SC12 with a power drill attached to the nose and a straight tube on the inlet. Theoretically, that should be a decent* simulation of an inlet runner as far as harmonics are concerned. I'm thinking for testing things like trumpet shape, variable inlet length setups, 'pulse plates' etc it should work.

I'm trying to work out a way of measuring the pressure waves inside the pipe without spending megabucks on testing equipment.

I can pinch a CRO from work, so a decent transducer would do the job, but I've got no idea what I'm looking for. I'd thought about a microphone, but I think the pressures involved would be too high for it.

Any suggestions?

* - The pulse wave is going to be very different to a 4 stroke engine, but there will still be a wave there, so it should be OK for testing purposes..

[takai]

Gee Ben, dont want to make things easy for yourself eh Need something to do on the long weekend?
No real thoughts just yet, but im interested in what you come up with.

[river]

Hi,

How much pressure do you think there will be?

seeyuzz
river

[The Witzl]

i was going to suggest looking at some Yokogawa equipment.... but then you said you dont want to spend megabucks....

A differential pressure sensor measuring pressure on either side of a reduction collar inside the pipe will be able to show you what is going on. Typically these are used for flow rate analysis, using the Bernoulli Effect, but should also show up pressure pulses.

Jaycar now sells a Motorolla D.P. sensor that would work a treat - but the pressure differential range is limited so you would have to do a little flow techtonics maths to work out the correct reducer to use.

You could also use a Karmon Vortex airflow meter.... since they are VERY accurate at the lower end of their flow rate scale. This also eliminates the need to make anything or revisit your physics text books in great depth.....

[Ben Wilson]

Jaycar now sells a Motorolla D.P. sensor that would work a treat - but the pressure differential range is limited so you would have to do a little flow techtonics maths to work out the correct reducer to use.

Didn't think Jaycar would have something like that, it's worth $40 to see if it works - thanks.

River - I have no idea, only one way to find out

[wilbo666]

0-1.45PSI...bah!

Let me know when the 3BAR ) (ABS) version comes in

Cheers
Wilbo

[The Witzl]

0-1.45PSI...bah!

Let me know when the 3BAR ) (ABS) version comes in

Cheers
Wilbo

did you read the part that says differential pressure sensor? That particular model is for precision measurement, not your meataxe manifold pressure sensing

... and jaycar probably wont carry it anyway

[Ben Wilson]

Just did some quick maths, used with a pitot tube as an airspeed indicator, that sensor should be good for around 240 knots (or 405 f/s). It could be good for an indicator for a flowbench as well....

[The Witzl]

Just did some quick maths, used with a pitot tube as an airspeed indicator, that sensor should be good for around 240 knots (or 405 f/s). It could be good for an indicator for a flowbench as well....

.... precisely the intended purpose my main man.

[wilbo666]

did you read the part that says differential pressure sensor? That particular model is for precision measurement, not your meataxe manifold pressure sensing

... and jaycar probably wont carry it anyway

Yes, yes I can read

And yes I understand what it means...but heck the pressure drop accross anything I'm likely to measure (IC, TB, etc) is prbly going to max that thing out

How about a 2bar differential

Cheers
Wilbo

[Rcubed]

are you think along the lines of the manometers, shown here?
http://stores.ebay.com.au/gastools
they've had a good write up on the resolution and accuracy. a little on the high $ side, tho

[ed]

but what are you measuring?

ultimately what you want to know is final cylinder filling (VE) and im not sure how youd do this

having a probe you could stick in the tube to measure pressure and location of nodes and anti nodes, confirming the induction of a standing wave, is cool, but useful? pressure at the back of the 'valve' would also be useful, but youll need to time this with the 'valve' opening and closing sequence - can you measure this?

i think what would be more useful would be a signal generator conneced to a small speaker on the end of a PVC pipe of X length, find a harmonic of this length with the signal generator, then add stuff like a bellmouth, a taper, a pulse plate etc etc and see what happens to the freq of the harmonic, and the volume of the released sound.

(which brings up a point - if youve got powerful reflection of waves, would expect the vol of the sound to be great or small? ie great sound implies loss of energyto the environment)

would it be possible to put an ameter in the speaker circuit to measure the current req to drive it? might be able to tell when the speaker bell is fighting destructive interference, or being 'helped' by contructive waves by the amount of power req to drive it?

my 0,02

cheers
ed

[mrshin]

How about a 2bar differential

For something as rough as that, why not grab a pair of old MAP sensors from the wreckers and just compare the output?

I think Ed might be onto something with the speaker idea, although maybe a speaker that small would be a bit hard to measure anything meaningful from???

I also don't know that an old blower would really be a great representation of an engine's intake pulses. I think the difference in the intake pulses would be far too great compared to an engine to learn anything of use?? To get the best out of a particular engine, surely the only way would be to do some testing in the very engine on an engine dyno. Hang on, didn't someone say something about cust cotting? *hangs head in shame*

[o_man_ra23]

I think Ed might be onto something with the speaker idea, although maybe a speaker that small would be a bit hard to measure anything meaningful from???

Easy enough to get a bigger speaker and tube it down. Otherwise Jaycar do some pretty good 3" speakers that you can get a decent pulse from

Cheers, Owen

[ed]

just thinking on my own question...

as i discussed here:
http://www.v-eight.com/tech_forum/viewtopic.php?t=138

the reflection co-efficient of the bellmouth is shit, and thinking about it - of course, what does every musical instrument have - a taper and a bellmouth

so once a harmonic is established for x length, then theres going to be a balabce between generating enough reflection to create a strong harmonic, and a loose enough end boundary (the bellmouth) to release this energy to atmosphere

cheers
ed

ps - why doesnt anyone ever join my forum - it makes me feel sad

*sigh*