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  • Wally Hayward
    replied
    Exhaust Gas Temps

    Interesting... seems to "prove" that the gas had a higher temperature gradient than I thought....
    The Westach is calibrated with a cold junction temperature of 24 degC and I believe quoted accuracy is +- 2% FSD.
    The digi meter is +-1% (+-1 digit) and may well include cold junction compensation.
    So both readings could be well within their respective tolerances of the "actual" temperature. "yer pays yer money and makes yer choice":-)

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  • Nick Axworthy
    replied
    Exhaust Gas Temps

    Wally took the hose clamp off the egt sensor...sits well inside the manifold now...agrees with the trikes own Westech gauge...well indicates 25c less but I somehow think the digital version is more accurate....must have not been sitting in the main flame path enough.

    Handy bit of test kit.

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  • Nick Axworthy
    replied
    Exhaust Gas Temps

    Sorry...of course I should have said 100mm 4"

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  • Wally Hayward
    replied
    Exhaust Gas Temps

    Good point.. I missed that...
    400mm from piston... presumably the skirt which from memory is approx 60mm from the flange?

    400mmm would equate to approx 4 times the "correct" distance.. so "anything could be correct":-)

    For the 503 and 582
    Quote from Statomaster.

    "The EGT probes are placed 38 mm (1 1/5 inches) from the engine exhaust port. Threaded bosses
    are normally welded to the exhaust for use with M8 x 1 thread EGT probes. Otherwize, holes are
    drilled and clamp-type EGT's are installed. "

    Attached files

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  • mikehallam
    replied
    Exhaust Gas Temps

    Nick,

    BTW. Your post at 10.24 this morning says the probes are 400 mm from the piston ?

    Shurely shome mistake ? As that's roughly 16 inches.

    [On their 912 4 strokes Rotax ask for 100 mm = 4"].

    FWIW. When my 447 was running EGT read 1250 F = 675 C. But as someone has pointed out, it's all relative when using such devices.

    mike hallam.

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  • Wally Hayward
    replied
    Exhaust Gas Temps

    I believe that it is generally accepted that the exhaust gas flow tends to have a temperature gradient in the "pipe" and slower, and of lower temperature, at the outside of the gas "column" (i.e closer to the pipe) being more pronounced at higher revs where I guess surface friction has a greater effect but I am surprised that even if the sensor was actually mounted on the "pipe" it would "stop" at 300C.
    However, exhaust gas flow, particularly in a 2 stroke with "tuned exhaust", even if only mildly tuned as in the Rotax, obeys the rules of a "black art":-).

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  • Nick Axworthy
    replied
    Exhaust Gas Temps

    Hi Wally...I ordered a seperate EGT type like the type we use...with the hose type clamp...it did go upto 600c when I put the sensor in a blowtorch burner for a few sec a few nights ago...so it will read higher...as you say...maybe I need to alter its mount to go deeper.

    Odd though...it was neck and neck at 300c.

    Nick.

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  • Nick Axworthy
    replied
    Exhaust Gas Temps

    PM sent Mick.

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  • Wally Hayward
    replied
    Exhaust Gas Temps

    Although in principle all "K type" thermocouples should give exactly the same output per degree, I assume that you are not using the "bead" type thermocouple which is standard with that meter?

    Rather strange that the meter only reaches 300C.
    I guess if the probe is not inserted as far5 into the tube, then it will tend to under read at higher revs as it could possibly be in the "cooler relatively static" outer layer of gas.

    One rather "drastic" way of bench checking that thermocouples/meters combinations are giving roughly the correct "high end" reading, is to "tightly wrap" the thermocouple in "thin" 6063 T6 or 6061 T6 aluminium and heat with gas blow torch (MAPP gas") until it melts
    6063 T6 melts between 615C and 654C
    or 6061 T6 between 582C and 652C

    Hope it helps

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  • Mick Broom
    replied
    Exhaust Gas Temps

    Hi,
    My thoughts on this and understanding are that the Rotax is set up for worse case and so is jetted for sea level. The result is that even out of the box it tends to run rich.
    As the carbs get some hours on this tends to get worse due to wear.
    Our cheap EGT instruments are a very good way of keeping an eye on things but unless you are comparing results with other engines are in my opinion best viewed on as an indication of change rather than an absolute value.
    It is useful to realise the results from the main jet and needle/needle jet are completely separate and operate at different stages of flight so if you want to effect a change I think you need to take into account these things as well to get the results you want.
    Changing the main jet for a smaller one will only effect the fuel burn on take off and climb out so if you are into cross country flying will only make a small difference where as the needle gives you the mixture in cruise so will make a difference.
    My personal choice is to stay with a slightly rich main jet and optimise the needle for the mixture.
    If the EGT readings get a bit high you can then either back off the power or give it full throttle both which will reduce the readings.
    This system if used sensibly gives you a safe way of setting the mixture with the benefit of less fuel, more power and a smother engine.
    Most concentrate on getting the main jet correct which if you were doing a bike would be the correct way but air-bikes are used slightly different.

    Leave a comment:


  • Nick Axworthy
    replied
    Exhaust Gas Temps

    A 165 jet and 162 thats only 3cc of petrol different...now I can never remember is that per minute or per hour....maybe you need a bigger step to see a difference.

    Question for you guys....if using a color-tune...what would we be looking for...is there a benchmark color.

    Nick.

    Leave a comment:


  • Nick Axworthy
    replied
    Exhaust Gas Temps

    Well I got one of these with an EGT probe.

    http://www.ebay.co.uk/itm/Black-Type-K-Digital-Thermometer-TM-902C-Thermocouple-Probe-50-to-1300-/281901918185?hash=item41a2a9e7e9:g:qFUAAOSwX~dWjB9 u

    To see how it compares with the Westach anolog instrument I did a side by side test...I have a probe in each branch of my 503 manifold giving me a reading from both cylinders...I removed one and replaced it with the new ebay one.

    At first the digi was giving an exactly the same reading as the analog gauge at 300c which was at around 2500rpm...on increasing the revs so my Westech was reading 500c the other digi type was still reading 300c.

    So not sure why that should be...the digi meter is running from a probe that does not sit as deep into the exhaust branch but they are both 400mm out from the pistion

    Any ideas wally.

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  • Guest's Avatar
    Guest replied
    Exhaust Gas Temps

    Just a thought where are the 'EGT probes situated - are they the correct distance from the cylinder wall?

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  • Aerials
    replied
    Exhaust Gas Temps

    Phil, have a look at this article, it might be useful: http://rst-engr.com/rst/articles/egtcht.pdf

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  • Phil Cater
    replied
    Exhaust Gas Temps

    Well....... The latest in the saga is that I've changed the main jets in the carbs to 162 size (from 165), expecting the EGTs to be a fair bit higher but......

    No difference. They're still both below 500 so I must draw the conclusion that the gauges are faulty. It looks like the needles rise to 480 or so then no higher. Bother! (other expletives deleted).

    What good are gauges if they tell porky pies I ask myself!

    Hopefully the external instrument I've ordered from Ebay (see earlier in this post) will arrive from China soon and I'll check the accuracy of my Shadow's gauges and report back.....unless anyone's got a spare EGT gauge I could borrow in the meantime for a day?

    I also intend to order a Colourtune plug!

    Phil.

    Leave a comment:

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