Spark plug temperature measurement with thermocouple type K

Hello,

As part of my Bachelor's thesis, I want to measure the temperature in the electrode of an engine spark plug using a type K thermocouple and implement it using Arduino. After reading some papers and forum posts, the main issue appears to be the high voltage generated during the ignition phase (~20-40 kV), which could damage the electronics without proper filtering and thermocouple isolation.

So, my questions are: Can this be achieved using Arduino? I have used Arduino for some home projects, but I am still a novice. Would the learning curve for something like this be too steep within the span of 4-5 months? What are the basic electronics and circuits I need to consider and research?

Think ...... It is your thesis......
The spark system at car motors are very sensitive too, if you put something near spark plug pin, nobody know what happened......
Spark can jump to other locations and affect engine operation.

Not by itself. You will certainly need to build some additional interference supression and isolation circuits for this particular application.

Would the learning curve for something like this be too steep within the span of 4-5 months?

That depends on your engineering experience and how smart you are

What are the basic electronics and circuits I need to consider and research?

Well, you might research about isolated/shielded thermocouples and thermocouple amplifiers

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How are you going to attach a thermocouple to the electrode inside the cylinder? Or are you going to measure the temperature at the external attachment for the ignition wire?

The temperature will vary a lot depending on the fuel mixture ratio, engine timing, etc.

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Does your spark plug use internal resistors? They will isolate the heat for the combustion chamber from the top of the spark plug. Tell us where you are making the temperature measurement.

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Have you considered contacting a spark plug manufacturer and see how they do the measurement.

The thermocouple would be going through the middle that means through the electrode but not all way through .

Yes it does, but the idea is that the thermocouple would be going through the middle of the electrode and through the said resistor.

Along side the centre conductor for the spark?
Why not all the way through, how are you going to reach the spark gap, where the electrode resides?
Have you built the modified spark plug yet?

You will have major insulation problems and noise/induced currents in the thermocouple lead from the HV conductor.

I'm not sure how physically a thermocouple junction would survive in the explosive and turbulent environment of the combustion chamber.

Tom... :grinning: :+1: :coffee: :australia:

The spark plug has been build yes.

I'm not sure how physically a thermocouple junction would survive in the explosive and turbulent environment of the combustion chamber

The thermocouple is not going all the way through the electrode into the combustion chamber because of sealing problems and as you mentioned the possible damage to the thermocouple. Is looks similar to this:

Placing the thermonuclear in the center leads causes it to face something in the 10-30kV range. How do you propose to isolate that from your instruments. The junction will probably survive as it is the two metals fused together.

How many of these do you have to test with?

You mean how many sparkplugs?

Maybe with an optocoupler ?

How many with the built-in thermocouple?

Not needed.
As I previously mentioned, you will certainly need to build some additional interference supression and isolation circuits for this particular application.

I think you need to study the physical properties of what you are trying to measure and its associated environment. Most Opto couplers will not withstand that high of voltage or the temperatures of the engine block. What did the spark plug manufacturer say? Try this link: https://www.sae.org/publications/technical-papers/content/2022-01-0565/

For starters just one, for the future 2 sparkplugs on one engine.

I still haven't received an answer. Another idea I had is to coat the thermocouple with an electrically insulating layer; however, further research would be needed to determine if there are any suitable materials for that purpose.

That will not prevent electromagnetic induction from the high voltage.
Isn't the thermocouple already isolaed from the engine ground?