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Post by azwood on Sept 12, 2018 2:39:45 GMT -5
Ok thanks ill hold off on the nozzle for now. Hi Don't fit a jet nozzle yet , far too early in the development . You need to run the engine without a nozzle to see what sort of temperatures the engine is producing at high power settings , then if they are "cool" (450-500C) , think about a nozzle and size it with consideration to the temps you've been experiencing . Prematurely fitting a jet nozzle can result in a dead engine very quickly :-( ............the backpressure from the nozzle will reduce the pressure drop across the turb stage which will require higher temperatures to "compensate" , those higher temps need more fuel which may or may not be combusted efficiently resulting in flames at the turb wheel . So please , go slowly , check that she can run up to high PRs on liquid fuel first , then if things are OK , think about the nozzle . Cheers John |
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Post by azwood on Sept 12, 2018 4:22:11 GMT -5
If i end up needing water injection is it best to do it through the sustain holes so it only efects tot's
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CH3NO2
Senior Member
Joined: March 2017
Posts: 455 
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Post by CH3NO2 on Sept 12, 2018 13:19:30 GMT -5
Not sure what sustain holes are but if you need to inject water, try injecting it just before the compressor inlet as a very fine mist. It can increase power potential the same time it lowers tot's.
Otherwise, you could try spraying water after the compressor or even through the Tertiary holes so it wont affect the combustion dynamics.
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Post by azwood on Sept 12, 2018 14:29:35 GMT -5
Not sure what sustain holes are but if you need to inject water, try injecting it just before the compressor inlet as a very fine mist. It can increase power potential the same time it lowers tot's. Otherwise, you could try spraying water after the compressor or even through the Tertiary holes so it wont affect the combustion dynamics. I thought spraying it before the turbine would have the most efect on turbine temps. |
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Post by racket on Sept 12, 2018 16:20:50 GMT -5
You shouldn't need water injection , if you still have excessive temperatures once running at higher PRs then you need to find the cause , simply spraying in water might only exacerbate the situation as that water needs to turn to steam and that steam needs to get through the "restrictions" of the turb stage , it could "displace" airflow in the process, pushing comp flow closer to surge .
Your comp and turb dimensions appear to be a reasonable match , there shouldn't be any temperature problems as long as the combustion is taking place as it should and there isn't a too restrictive "exhaust" .
Cheers
John
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Post by azwood on Sept 12, 2018 17:00:42 GMT -5
Maybe i need to add some vains to the outer can just above the tursury zone to slow the air down and favor those holes a little more.not sure im learning as i go here lol.id be lost without you guys pointing out things i dont see.
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Post by azwood on Sept 12, 2018 17:07:49 GMT -5
Im not sure i trust my pyro gauge might need to check it against anouther one to be sure.
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Post by racket on Sept 12, 2018 18:40:54 GMT -5
Until you have the engine running at a measured ~5-7 psi P2, any temp readings will be inconclusive , even a very well sorted engine running at barely self sustain will have high temps , but they soon drop once up to a healthy idle rpm , if you look at any compressor map you'll see how the efficiency islands are configured , and its not until a PR of ~1.5 :1 ( 7 psi P2) that we start to get into good efficiencies , below that the efficiencies can be very poor if the flow deviates a bit one way or the other from ideal flows , also turbine efficiency is poor at low rpm , the two combined makes for the necessity of high temps to provide the required power to drive the comp ...............get the rpm up and things should be fine :-)
Cheers
John
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CH3NO2
Senior Member
Joined: March 2017
Posts: 455
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Post by CH3NO2 on Sept 13, 2018 15:18:19 GMT -5
I thought spraying it before the turbine would have the most efect on turbine temps. Hi Azwood, Not really. Where ever it's injected it takes the same amount of energy to heat the water to a given TOT temperature. One BTU is the amount of heat energy required to raise one pound of water by 1ºF. One pound of steam contains ~1150 BTUs. This is the energy you need to put into the water for it to evaporate if you start with water at 32F. If you start with warm water at 100F the water already has 68 BTU/lb so the BTUs required to evaporate the water when you start at 100F is 1150-68 = 1078 BTU. Assuming all other variables are held constant, where the water is injected (before the compressor or inside the flame can) it wont really make a difference to the TOT as long as all the water is vaporized, mixed and goes through the system. On a side note: There is however a modest performance advantage when the water is injected as a fine mist before the compressor inlet. The mist cools the air before it enters the compressor, giving the air a slightly higher density. The higher density air results in a higher air mass flow rate which means the engine can inhale the air at a higher rate. ~20% increases in thrust have been documented with water sprayed into the inlet of larger engines. But like John wrote, you dont want to experiment with water injection until you get everything sorted out and your engine design is fully optimized. When its running good, then you can experiment with water injection to see what the effects are. Good luck with everything! You are cranking out the fabrication at an amazing rate! Tony |
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Post by racket on Sept 13, 2018 16:42:28 GMT -5
Hi Tony
I experimented with water injection back in 1999 with my TV84 engine , I used ~1.5 liters/minute of water or ~3% W/W with air , rather crudely injected around the FOD screen .
TOT was down , but thrust didn't seem to change , water vapour is less dense than air , and due to the extremely short time frames with our engines , its less than a millisecond between inlet and outlet of the wheel, evaporation is compromised , then theres the fact that temps never reach boiling point within our wheels unlike a multistage compressor .
A fair bit of the gain in performance from water injection in aero engines is derived from using less power to compress the "cooled" air in the latter stages of those multistage comps .
My conclusion was that its a waste of time on our engines, too much complication for very minimal results , its value would be in an engine with an oversized turb stage that would normally have the comp flowing in an inefficient region of the map towards choke , adding water should bring airflow back into more efficient regions increasing thrust and in combination with the increase in mass flow from the water additional thrust .
I've heard that a very finely atomised spray of methanol well upstream of the comp inlet can increase mass flow due to the much faster evaporation rate of methanol
Cheers
John
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Post by azwood on Sept 13, 2018 17:25:11 GMT -5
Hi Azwood, Not really. Where ever it's injected it takes the same amount of energy to heat the water to a given TOT temperature. One BTU is the amount of heat energy required to raise one pound of water by 1ºF. One pound of steam contains ~1150 BTUs. This is the energy you need to put into the water for it to evaporate if you start with water at 32F. If you start with warm water at 100F the water already has 68 BTU/lb so the BTUs required to evaporate the water when you start at 100F is 1150-68 = 1078 BTU. Assuming all other variables are held constant, where the water is injected (before the compressor or inside the flame can) it wont really make a difference to the TOT as long as all the water is vaporized, mixed and goes through the system. On a side note: There is however a modest performance advantage when the water is injected as a fine mist before the compressor inlet. The mist cools the air before it enters the compressor, giving the air a slightly higher density. The higher density air results in a higher air mass flow rate which means the engine can inhale the air at a higher rate. ~20% increases in thrust have been documented with water sprayed into the inlet of larger engines. But like John wrote, you dont want to experiment with water injection until you get everything sorted out and your engine design is fully optimized. When its running good, then you can experiment with water injection to see what the effects are. Good luck with everything! You are cranking out the fabrication at an amazing rate! Tony Thats intersting info.i have been told injecting water pre compressor can increase the peak flow on a piston engine anyway.ill test it again on the weekend i got the pyro sorted last night so it going good now ambient temp readings are correct.where before ambient was showing 170 |
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Post by azwood on Sept 13, 2018 17:27:37 GMT -5
Hi Tony I experimented with water injection back in 1999 with my TV84 engine , I used ~1.5 liters/minute of water or ~3% W/W with air , rather crudely injected around the FOD screen . TOT was down , but thrust didn't seem to change , water vapour is less dense than air , and due to the extremely short time frames with our engines , its less than a millisecond between inlet and outlet of the wheel, evaporation is compromised , then theres the fact that temps never reach boiling point within our wheels unlike a multistage compressor . A fair bit of the gain in performance from water injection in aero engines is derived from using less power to compress the "cooled" air in the latter stages of those multistage comps . My conclusion was that its a waste of time on our engines, too much complication for very minimal results , its value would be in an engine with an oversized turb stage that would normally have the comp flowing in an inefficient region of the map towards choke , adding water should bring airflow back into more efficient regions increasing thrust and in combination with the increase in mass flow from the water additional thrust . I've heard that a very finely atomised spray of methanol well upstream of the comp inlet can increase mass flow due to the much faster evaporation rate of methanol Cheers John I will see what my tot's say next run i agree not worth doing water injection if i dont need to. |
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Post by azwood on Sept 16, 2018 4:05:53 GMT -5
Ive done a few more things over the weekend made a better gasket for the base and went over everything.also bent the tursurey holes to get more air from the direction of flow we'll see if any of this makes a difference to tot's.   |
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Post by azwood on Sept 19, 2018 15:06:57 GMT -5
Got it running on kero a few things need addressing like the top gaskit but it runs great temps are between 550 and 650c.  |
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BFTO
Veteran Member
Joined: February 2016
Posts: 128
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Post by BFTO on Sept 19, 2018 15:19:08 GMT -5
650c without nozzle?
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Hi 
