Tuesday, April 5, 2016

Air Temperature and Head Temperature

Another beautiful day in interior Alaska. I stopped at Creamer's Field Migratory Waterfowl Refuge to see how many birds were there. A few weeks ago, they had cleared away much of the snow exposing the grass. There were a few birds though not as many as there are a little later in the Spring. Both of these pictures are HDR using the built in iPhone camera app.

I had a lot of errands to run this morning so this was a nice place to stop and enjoy the quiet. It's predicted to be over 50°F by mid-week so I may as while enjoy the cool weather while I can.

I have been curious about the accuracy of the CHT (cylinder head temperature) gauge. The one I have is not temperature compensated so it only reads "right" at +70°F. Today the outside air temperature was about 40°F so the CHT will be reading about 30°F high. Right after pulling into the garage, the left cylinder read 355°F (or 325°F after adjusting for ambient temperature) and the right was 375°F (or 345°F).

I picked up a relatively cheap IR thermometer on Amazon and it read; left 277°F, right 298°F. So both sides of the CHT are reading about 50°F too high. Like any IR thermometer, the surface temperature is estimated by measuring the thermal radiation received by the sensor.

At a distance of a foot, the spot size is a little over an inch in diameter. The temperature reading is affected by the emissivity of the surface which is a quantitative measure of the efficiency in radiating thermal radiation. The device assumed an emissivity of 0.95. A dark, non-reflective surface would have an emissivity near 1.0 and a reflective mirror would be 0. To get an accurate reading, the emissivity needs to be near 1. I'm guessing that the cylinder head isn't a perfect 1.0 but it's not far off. Not having access to a portable IR spectrometer, I could simply paint a section of the head with flat black paint and that would raise the emissivity to get a more accurate reading. But I'm thinking that this is close enough. And I can probably just assume that the temperature compensated temperature from the CHT thermocouples is a bit high.

Monday evening was the monthly Airhead.org get together at the Silver Gulch microbrewery in Fox, AK. Today was the first time that there was another bike there since October. There was a pretty good turnout and there was even a donated t-shirt for a give away. The roads were is great shape and I took the Ural over the hilly road with a lot of running in 2nd and 3rd to avoid lugging the engine. Even with the hills, CHT were around 280°F by the time I got home.


2 comments:

redlegsrides said...

I assume the IR thermometer was calibrated on a "known" temperature object? I think I'll take mine along next time I go riding to compare against what I am seeing from the Trailtech sensors.

RichardM said...

"Calibration" target was a black anodized aluminum plate (smaller pan lid) floating on boiling water read 210°F. Seemed close enough for a Ural. ;-)