i was looking through my stash of tech articles and happened upon a Gordon Jennings/Cycle Magazine piece from 1978. "Two stroke oil premix ratios"

"Unfortunately, this brief full-throttle blast had sent the spark plug washer temperature soaring up into the 435 degree F twilight zone very rapidly. Subsequent examination of the spark plug indicated there was a bit too much timing advance which we then set about correcting.. ....... bring the spark plug temperatures into the 390-400 range"

most private airplanes use a cylinder head temperature (CHT) sensor.

i consider our rotary motors to be 2 cycle in that every compression stroke is a power stroke. our motors are liquid cooled as opposed to the air cooled motor in Cycle Magazine so perhaps our temps will be different but there is no question that CHT may offer additional help as to timing dynamics. the "cylinder head" is going to be the rotor housing which includes coolant passages. the other face of the sensor contacts the sparkplug.

has anyone on the forum used a CHT sensor? they are available as Type K. i recently upgraded my EGT amp to The Sensor Connection item and it has 8 inputs. i am currently using four so it won't be a big deal to add four CHTs.

not only will the temps be interesting but it will also be interesting to see if there is much diff between the front and rear.




here's the link to the sensor:

https://thesensorconnection.com/prod...al-type?v=2378

link to the 8 channel thermocouple amp. a high quality piece IMO

https://thesensorconnection.com/prod...-outputs?v=789

 

I'll grab some too and start logging then once I fire up my engine.

 

i was a bit bummed after i noticed that the response time was 1.5 seconds. given the typical egt K thermocouple is 4 per second and given that the last pull i did in 3rd gear from 72 to 112 was 1.67 seconds and given that ATM the only thing of interest is the March Tex Mile... i was thinking it might not be valuable to me. then i remembered there were 3 on the site. the second was a J thermocouple and had the same slowish response time. the third was a K but has a response time of half a second. sign me up. after a look at the rotor housing spark boss area i am going to have to do a bit of Dremeling but nothing difficult.

here's the trick CHT sensor:


the actual link so you can see additional pics

https://thesensorconnection.com/prod...em-type?v=2638

 

You need to be a bit realistic about how effective they can be as an under plug sensor in terms of thermal mass and lag, there is a lot of material between the chamber the plug boss, if you want faster response you really need to drill into the back of the steel liner. That step response will be fine as a comparator to coolant temp or to hopefully identify coolant/flow loss in applications where a loss sensor isn't present.

 

"You need to be a bit realistic about how effective they can be"

even a cursory read of my two posts, "may offer additional help," would lead to the conclusion that it is purely an R&D/satisfy curiosity deal on my part and not much of a gamble for just over $100. my interest does not extend to messing w the steel liner although i grant you the numbers would be interesting.

 

Since these temps are not used as inputs for any sort of tuning, the readings will still be interesting and insightful for how hot they are getting despite the lag from the sensor and whatever buffer the thermal mass of the housing and water cooling create.

 

I'm just saying getting hung up on step response time of a sensor without considering the system is wasted effort.