What thermocouple type for EGT measurement ?

[Warpspeed]

What is the most frequently used thermocouple type for exhaust gas temperature measurement for gasoline engines ?

There are all sorts of conflicting requirements including temperature measurement range, millivolt output, and life in oxidizing/reducing atmospheres.

I am just wondering what you guys are using ?

 

[dynoguy]

The t/c's I've used for egt over the years have been the common type K's, which I think are good to 2000 F. One tip though, when you're setting up your data display, skip the decimal places, cuz they don't resolve that fine.

 

[Warpspeed]

Thanks, Dynoguy.

I was wondering about suitability of K type, they have a nice high millivolt output, and survive o/k in a slightly oxidising atmosphere, and are relatively low cost and easy to obtain.

But is 2000F (1093C) really high enough on a flat out high specific power racing engine ? The thermocouple tables stop at 1370C. I know we definitely don't want to run lean, and there should be about zero oxygen, but I was hoping to be abe to measure up to higher temperatures. Is that a realistic wish ?

Do you slip your EGT thermocouples in a stainless steel well, or do you run it naked in the exhaust stream ? I can see advantages both ways.

 

[NickE]

You might want to look at Omega's site, also they'll send you their catalogs free... I think a thin and small inconel thermowell would provide the longest life to the thermocouple, naked in the stream would give the fastest reaction time. You should be able to read to higher temperatures than 2000F, I've seen type K's put into molten iron baths at 2800F, It destroys the couple quickly though.

http://www.omega.com

Nick
I love materials science!

 

[pulsewidth]

Warpspeed,

You shouldn't see temps that high, unless something is wrong (like
retarded timing)

There is a tradeoff between response time and sensor lifespan.

Top Fuel Drags typically use naked end 1/4 in. dia. K type for EGT.
They won't last forever but they respond quickly.

Good success using 1/8 closed end K type for Road racing for multi-hour endurance racing...and the fitment on the exhaust to hold the sensor is smaller and easier to fit in place.

 

[Warpspeed]

Thank you all for helping me with this.

It looks like K type is the go then. They are cheap enough to keep replacing, and a naked thermocouple would respond almost instantly in a high velocity exhaust stream.

This is for an engine dyno, so thermocouple life is not a big issue.

 

[GT6Steve]

I've been using a roll of K type thermocouple (NOT extension)wire to make my TC's. Just twist the ends tightly and sandwich it between two manifold gaskets. Brazing the joint makes it last longer but is not really necessary. Omega has it and one roll should last you a LONG time. HTH, Steve

 

[NickE]

"Just twist the ends tightly and sandwich it between two manifold gaskets. Brazing the joint makes it last longer but is not really necessary."

You can also buy clips that you crmp on the end and the couple lasts even longer. Although if you are looking for minimum response time you might want to find a way to make teh really little tiny weld beads of alumel and chromel that are on omega's fastest responding TC. I have some that are made with wire <0.012" dia and w/ a bead on the end that is <0.020".

nick

 

[ntc490]

Do you have a part number for the wire you use?

 

[btrueblood]

You can make a small t/c spotwelder using a capacitor-discharge. Get a bunch of old electrolytic capacitors of 25+ vdc working voltage or better, and wire them to a stack of batteries via an intermittent switch. A set of welding leads, one of which terminates in a pointed piece of graphite (like an old-fashioned drafting lead), the other a flat piece of graphite or copper. Lay the twisted strand down on the flat electrode, then bring the pointy electrode into contact with the end of the twisted pair - zap!

This worked well for me using ~22 ga. t/c wire, and with 27 vdc and about 1 F of total capacitance. I found the "best" combination by starting with a bunch of 10,000-25,000 uF cap's from junked power supplies, and ganging them in parallel until I was happy with the results.

Good luck,

Ben T