Car exhaust pressure and gas flow measurement?

[wsjoe]

What type of sensor is best suited to measure pressure in the exhaust (muffler) at high temperatures of the exhaust (around 1000F)? I want to measure the pressure at different points of the exhaust and see how they change as engine rpm varies. Which sensor do you recommend? What is the range of pressure of a typical engine?

Would a pitot tube be adequate to measure the air flow (velocity) also for high temperature application? What manufacturer would you recommend?

I think the exahust of a gasoline and diesel engine can reach 1200 deg F.

 

[andyv8]

To get stable pressures from an exhuast pipe, you need to pipe from 3 points equally spaced (120°) around the pipe diameter which are then fed together in to another tube which has a standard pressure gauge on the end. Without this manifold arrangment, you'll tend to pick up all the pressure spikes from the exhaust valves. The manifolding arrangement will also mean that your pressure gauge shouldn't see very high temperatures.
You shouldn't see more than 1 bar gauge pressure unless the exhaust system is REALLY bad.

Andy

 

[andyv8]

Forgot to mention, II'd normally use about 12" of 3-4mm diameter pipe between the exhaust and the pressure transducer

 

[wsjoe]

Thank you andyv8 for your recommendation.

Which pressure transmitter have you used? I want to collect data and pick them up from a computer. I guess I can use Labview for data acquisition, but this is kind of expensive. Have you seen cheaper alternatives?

Know anything about pitot tubes used to measure flow (velocity) in the exhaust?

thanks

wsjoe

 

[andyv8]

A std Druck transducer will do the trick, just depends on what kit you've got to log it with. I've done all of my testing on dyno's, so used the dyno gear instead of stand-alone systems.

I'm afraid I've never attempted to measure flow in the exhaust, but I think the best way would be to measure pressure before and after a laminer flow element (like a catalyst) after calibrating on a flow bench.

Andy

 

[Janetm]

Hi there,
As far as a sensor goes, I have found that if you go down to the local scrap yard and find a boost sensor from a turbo vehicle. These work well as they usualy work off 5 volts (some 12 volts battery voltage). They are generaly 3 wire sensors -volts +volts and a signal out.The nice thing about them is that they have amps, filters etc already built in so the signal out is clean and repetitive.

 

[WiringGuy]

You could also use an Annubar to avg. the pressure in the tube. Personal I just have a single port flush with the wall of the tubing and don’t have any major pressure pulses but it’s just a 4 cyl.
Andy do you use any liquid to isolate the exhaust gas from the sensor element? When I did my install I used 14” of ¼” tubing bent in an S shape. I filled the last 8” with 10w shock oil because I was scared that the sensor would have a short life when exposed to high temp exhaust gas and also to trap any soot particles. I’ve only had it in the car for about two months but so far all is well.

 

[andyv8]

WiringGuy - I've never bothered to isolate the exhaust gas from the sensor element - but then all of my work has only involved short duration dyno testing - I've never tried leaving one in place for extended periosd.