|
Post by racket on May 19, 2020 19:13:57 GMT -5
Hi Luke jetandturbineowners.proboards.com/thread/680/diy-turbinesTIT is turbine inlet temperature , which isn't measured as its not safe to do so as the thermocouple may fail and go through the turb wheel , TIT is calculated back from TOT using the temp drop thats required across the turb stage to power the comp , TIT is used for overall engine calcs, more of an academic number, as long as TOT/jetpipe temps are kept to the design level( ~600 - 650 C) then things should be OK. P1 is simply atmospheric pressure , no need to measure it unless you want to do very detailed calcs , not necessary for us DIY'ers. P2 needs to be measured in a "quiet corner" of the combustor where air speeds will be relatively low Cheers John
|
|
lukenz
Member
Joined: October 2018
Posts: 35
|
Post by lukenz on May 22, 2020 3:04:30 GMT -5
Hi Luke jetandturbineowners.proboards.com/thread/680/diy-turbinesTIT is turbine inlet temperature , which isn't measured as its not safe to do so as the thermocouple may fail and go through the turb wheel , TIT is calculated back from TOT using the temp drop thats required across the turb stage to power the comp , TIT is used for overall engine calcs, more of an academic number, as long as TOT/jetpipe temps are kept to the design level( ~600 - 650 C) then things should be OK. P1 is simply atmospheric pressure , no need to measure it unless you want to do very detailed calcs , not necessary for us DIY'ers. P2 needs to be measured in a "quiet corner" of the combustor where air speeds will be relatively low Cheers John Thanks for clearing that up John. Started her up again today, end cap still glowing, so back to the drawing board there, also had big issues starting the engine, I think the spark plug is to far away from the spray pattern so maybe going to install a pilot butane system. As far as temperatures go I only had time to use the thermal infrared gun. I was getting 250C on the turbine outlet pipe, so surprisingly on the cool side at full throttle, the glowing face on the front of the flame tube as seen in last weeks video was 298C. Cheers, Luke
|
|
|
Post by racket on May 22, 2020 3:43:04 GMT -5
|
|
lukenz
Member
Joined: October 2018
Posts: 35
|
Post by lukenz on May 22, 2020 3:49:31 GMT -5
Hi John, I thought that temp was to low for glowing, I was sceptical so will be wiring up thermocouple before next run.
|
|
arthuro
New Member
Joined: May 2018
Posts: 3
|
Post by arthuro on Apr 9, 2021 4:50:38 GMT -5
Hi Luke jetandturbineowners.proboards.com/thread/680/diy-turbinesTIT is turbine inlet temperature , which isn't measured as its not safe to do so as the thermocouple may fail and go through the turb wheel , TIT is calculated back from TOT using the temp drop thats required across the turb stage to power the comp , TIT is used for overall engine calcs, more of an academic number, as long as TOT/jetpipe temps are kept to the design level( ~600 - 650 C) then things should be OK. P1 is simply atmospheric pressure , no need to measure it unless you want to do very detailed calcs , not necessary for us DIY'ers. P2 needs to be measured in a "quiet corner" of the combustor where air speeds will be relatively low Cheers John Hi all, My first post here. I did a lot of reading instead over time. Still i have a question. "P2 needs to be measured in a "quiet corner" of the combustor where air speeds will be relatively low" Do you mean really IN the combustor? maybe i have a different idea of "combustor", but it must be measured some where between the gab of outer chamber and flametube, right? Arthur.
|
|
|
Post by wannabebuilderuk on Apr 9, 2021 11:10:51 GMT -5
Hi Arthur,
Yes that's correct, the connection to the gauge is on the side of the combustion chamber opposite the side where the air is fed in from the compressor. It measures the pressure inside the chamber, between the wall and flametube.
Ben
|
|
slittlewing
Senior Member
Joined: November 2017
Posts: 458
|
Post by slittlewing on Apr 9, 2021 13:23:58 GMT -5
Hi Arthur,
I measure P2 using a port in the compressor housing, often used for wastegate actuator. This works fine. Pressure is the same everywhere after the compressor wheel!
Cheers
Scott
|
|
|
Post by racket on Apr 9, 2021 17:20:06 GMT -5
Hi Scott
I might need to "correct" your Reply a tad ................."Total" pressure is basicaly the same after the comp wheel , but the Static pressure which is what is generally measured as our P2 will depend on what percentage of Total pressure is made up of velocity Dynamic pressure.
If we measured Static pressure at the wheel exit it would be rather "low" due to the high velocity dynamic component of the Total pressure at that position, a pitot tube at the comp wheel exit would read Total pressure which would be similar to a Static pressure reading "in a quiet corner of the combustor" .
The wastegate pressure pickup point will be "under reading" your P2 pressure by a small amount due to the reasonably high speed of the air within the scroll , it might only be a few hundred feet per second but its still represents dynamic pressure that can be converted into static pressure .
Also , unless the pickup oriface is correctly aligned there could be other "variables" introduced, the pickup point is convenient to use though and shouldn't cause any problems if used :-)
Cheers John
|
|
slittlewing
Senior Member
Joined: November 2017
Posts: 458
|
Post by slittlewing on Apr 9, 2021 21:53:46 GMT -5
Good point John - I stand corrected 😁 On the holset turbos though, the wastegate point is in the “dead headed” or closed out portion of the compressor housing scroll, where there shouldn’t be much airspeed 👍 Cheers Scott
|
|
|
Post by racket on Apr 9, 2021 23:11:24 GMT -5
Hi Scott
Ah , I see what you mean , the scroll is sorta to the "side" of the diffuser passageway , there'll still be a fair speed of air , but we're only talking parts of 1 psi for most scrolls , its actually less than the static pressure drop at the inducer , some inducers must lose up to ~2 psi of static pressure due to the high inlet speeds , same 14.7psi of Total pressure but divided up 12.7psis plus 2.0 psid.
It'd be an interesting exercise to measure any difference in P2 between scroll port and at the combustor .
The "to the side" scrolls must have a helical airflow from the scroll , I wonder if thats a problem we need to consider , have to think on that :-)
Cheers John
|
|
arthuro
New Member
Joined: May 2018
Posts: 3
|
Post by arthuro on Apr 10, 2021 10:42:04 GMT -5
Hi Arthur, Yes that's correct, the connection to the gauge is on the side of the combustion chamber opposite the side where the air is fed in from the compressor. It measures the pressure inside the chamber, between the wall and flametube. Ben Thanks. I'm going to make a connection port on the chamber, on the radial opposite of where the pipe from the compressor comes in. Will the pressure be +- the same over the whole length of the chamber? you said: "opposite the side where the air is fed in from the compressor.". You ment this only in radial direction, or also axial direction of the chamber? scott, i do not have a waste gate actuator port, but it is a nice elegant position for a sensor. thanks. Arthur
|
|
|
Post by racket on Apr 10, 2021 17:21:10 GMT -5
Hi Arthur There'll be minor changes in static pressure at different positions within the combustor, but most pressure gauges we use will have more inbuilt inaccuracies , as long as you use a reputable quality gauge don't be too concerned about the fractions of a psi that might exist from different positions . This pic of my GT6041 build jetandturbineowners.proboards.com/attachment/download/216 shows where the P2 pickup was positioned "in a quiet corner" where the airspeeds were relatively low , anywhere under 100m/s-300ft/sec is preferable. Cheers John
|
|