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Post by racket on Dec 7, 2020 2:56:54 GMT -5
No
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Post by wannabebuilderuk on Dec 7, 2020 2:58:25 GMT -5
The rpm is controlled by the amount of fuel going to the engine, if you pump over the max amount then you can overspeed/overheat the engine and cause a catastrophic failure, you need to put all the fuel after the turbine and in the afterburner assembly or you won't have much of an engine left
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Post by Richard OConnell on Dec 7, 2020 12:13:48 GMT -5
wannabebuilderuk is absolutely right. Dont modify the amount of fuel you are dumping into the injectors in the flametube. Thats, in a sense, your engine throttle and you'd be throttling it higher than it was designed to run. It would likely cause much more flame than your combustor was designed to contain and it would melt your turbine. Only add fuel (diesel, kerosene, or Jet A) after turbine and inside the tailpipe with spray bars. The airflow from the engine will provide you all the oxygen you need to be able to light your afterburner. Once your afterburner is lit, watch for RPM drops or rising temperatures. burning fuel before a nozzle will add some resistance to the exhaust air thats trying to exit your engine and can also be catastrophic if left unchecked.
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Toni
Member
Joined: December 2020
Posts: 26
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Post by Toni on Dec 7, 2020 14:10:49 GMT -5
Thank you for that information to all of you.
Hypotetical situation: If I spray more and more fuel to flametube, which option happened first, compressor can not push enough air and flame choke and I have a lot of smoke, or it will melt or explode?
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Post by Richard OConnell on Dec 7, 2020 14:40:00 GMT -5
Unless you're pushing an insane amount of fuel into the tailpipe, I couldnt see a fast failure happening. Watch your RPMs and EGTs. If you have too much restriction at the nozzle with afterburner lit, you can either reduce fuel entering the afterburner or open up the diameter of the nozzle a little.
You'll lose out on some thrust when afterburner is not running if you open up the nozzle, but it will also allow for you to burn more fuel and affect the upstream engine less. Fighter jets use variable nozzles to get around this problem, but they're difficult to make for stuff in the scale we work on:
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Toni
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Joined: December 2020
Posts: 26
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Post by Toni on Dec 8, 2020 2:18:04 GMT -5
I mean if I spray insane fuel to combustion chamber, will it choke because too less air or will it explode because of over rpm?
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Post by racket on Dec 8, 2020 5:05:48 GMT -5
Too much fuel will accelerate the rotor to higher rpm possibly to overspeed , the extra fuel will increase temperatures entering the turbine stage causing overtemperature , BOTH of which can cause the death of your engine and possibly yourself if you get hit by a chunk of white hot metal travelling at supersonic velocity ...............other than that , its also a waste of fuel
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Toni
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Joined: December 2020
Posts: 26
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Post by Toni on Dec 8, 2020 5:39:54 GMT -5
Thank you John
As you calculate before, my HX60 is also 76 mm intake (3"), so I assume max fuel to combustion chamber is also 12,5 gal?
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Post by racket on Dec 8, 2020 15:39:25 GMT -5
There are often large deviations from the theoretical amount of fuel required depending on the engine build's configuration of parts etc etc etc ......
To minimise the risks its best to be "underfuelled" for the initial first few spoolups until one knows exactly how the engine is behaving , then and only then , increase your fueling capacity to explore higher power settings .
Its very easy to have a dangerous situation develop within a few seconds of your first spoolup if theres too much fuel made available to the engine .
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Post by turboron on Dec 8, 2020 21:21:26 GMT -5
toni, this is a good time to point out the liquid fueled combustors need a spring loaded drain valve or a weep hole to prevent fuel accumulating in any low spots. Whittle's engine ran away during development due to fuel buildup.
Thanks, Ron
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Toni
Member
Joined: December 2020
Posts: 26
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Post by Toni on Dec 20, 2020 2:34:21 GMT -5
Many thanks for all advices. Should I install EGT gauge before or after exhaust housing?
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Post by racket on Dec 20, 2020 2:41:48 GMT -5
after turbine wheel
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Toni
Member
Joined: December 2020
Posts: 26
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Post by Toni on Dec 20, 2020 2:53:25 GMT -5
I drive tractor pulling few years ago, there we measured EGT and pressure before turbine wheel, why after in these case?
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Post by racket on Dec 20, 2020 5:07:28 GMT -5
Because theres always the possibility of the thermocouple failing and going through the turbine wheel :-(
Its standard turbine practice to have it after the wheel , we can calculate the temperature drop across the stage if we want turb inlet temps , the "after" temperature is always cooler which provides a bit more of an easier life for the thermocouple as well
Cheers John
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Post by Richard OConnell on Dec 22, 2020 9:35:48 GMT -5
Also, in terms of an EGT, the "G" doesnt become "E" until after the turbine. Haha, in all seriousness, John's answer was really good. Sampling temps post-turbine means theres one less part that could break free and destroy the turbine.
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