Any one here ever experiment with water/methanol injection systems on small factory built turbines? I just had a call from a guy that builds jet dragsters and he suggested to try this for up to a "possible" 30% gain in dynamic thrust.
Told me to start with Mass Flow per second (in lbs) divided by 25 to get the amount of liquid per second to atomize into the compressor and use a 75 Meth/25%Water mix. And Quote ..."wont hurt the engine"
Im all ears.
Grand Bob Jet Luger
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Compressor Injection
Moderator: Mike Everman
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Lugebob
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Compressor Injection
Bob Swartz
Work Hard Play Harder
Work Hard Play Harder
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racketmotorman
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Hi Bob
I've experimented with water injection , but there are "complications" , not as easy as your "friend" suggests :-(( and even harder to get "right" at smaller scales.
Firstly we need to get the "liquid" to fully vapourise prior to entering the compressor so as to get full value from the latent heat of evaporation , and then not advisable to use below 40 deg F (ambient) as ice formation can be a problem .
Secondly , unless you want to reschedule your fuel flow its advisable to use a mix comprising 36% by weight of methanol ,64% by weight demineralised water, so that the heat release of the methanol balances the "cooling " effect of the water.
Thirdly , the very small time frame involved when air is passing thru a single small centrifical compressors does present problems if the injected fluid is still in an unvapourised state when injected in front of the compressor ,there simply isn't time for the cooling effects to work and increase mass flow .
With multistage full sized aircraft engine compressors there is plenty of time for "cooling" during the various stages and especially at the high pressure end where air temps are well above the boiling point of water , but in our "low compression" engines that temp isn't reached in the compressor wheel , but in the diffuser where it could have unintended negative consequences with regard the comp flowing continuing to flow in its high effic band .
Also, that hypothetical 30% increase has to come from somewhere , and the question neeeds asked , how is a fixed jet nozzle going to cope with the changing parameters ??
Also, (there heaps of them) , what happens to an alloy comp wheel subjected to liquid hitting its inducers leading edge at ~sonic velocities , certainly different to it hitting a stainless steel or titanium full sized comp .
How is the turbine stage going to "swallow" the extra mass efficiently ??
Water vapour takes up "space"
etc etc etc ..............be very careful about "expert advice" :-))
On the Allison 250 engine (air mass flow ~3.6 lbs/sec ) , the "fluid"(2 parts water , 1 part methanol) was injected at the rate of 1.2-1.3 gal/m at 40 psi , this provided a mere increase in horsepower from 25 hp from its normal 310 to 335 hp . This was injected into a multistaged axial compressor where the cooling effects, in what would normally be the hotter stages, made compression of the air easier , (and possibly increased mass flow marginally ??), giving the gasifier turbines an easier time , leaving more energy for the freepower turbines to extract .
My water injection experiments back in 1999 were inconclusive , there was a drop in TOTs but not any great change to thrust levels , possibly with some minor changes to fuel flows there could have been some , but certainly not 30% , maybe ~5%
I was injecting straight water at ~36:1 air/water ratio
Hope this helps
Cheers
John
I've experimented with water injection , but there are "complications" , not as easy as your "friend" suggests :-(( and even harder to get "right" at smaller scales.
Firstly we need to get the "liquid" to fully vapourise prior to entering the compressor so as to get full value from the latent heat of evaporation , and then not advisable to use below 40 deg F (ambient) as ice formation can be a problem .
Secondly , unless you want to reschedule your fuel flow its advisable to use a mix comprising 36% by weight of methanol ,64% by weight demineralised water, so that the heat release of the methanol balances the "cooling " effect of the water.
Thirdly , the very small time frame involved when air is passing thru a single small centrifical compressors does present problems if the injected fluid is still in an unvapourised state when injected in front of the compressor ,there simply isn't time for the cooling effects to work and increase mass flow .
With multistage full sized aircraft engine compressors there is plenty of time for "cooling" during the various stages and especially at the high pressure end where air temps are well above the boiling point of water , but in our "low compression" engines that temp isn't reached in the compressor wheel , but in the diffuser where it could have unintended negative consequences with regard the comp flowing continuing to flow in its high effic band .
Also, that hypothetical 30% increase has to come from somewhere , and the question neeeds asked , how is a fixed jet nozzle going to cope with the changing parameters ??
Also, (there heaps of them) , what happens to an alloy comp wheel subjected to liquid hitting its inducers leading edge at ~sonic velocities , certainly different to it hitting a stainless steel or titanium full sized comp .
How is the turbine stage going to "swallow" the extra mass efficiently ??
Water vapour takes up "space"
etc etc etc ..............be very careful about "expert advice" :-))
On the Allison 250 engine (air mass flow ~3.6 lbs/sec ) , the "fluid"(2 parts water , 1 part methanol) was injected at the rate of 1.2-1.3 gal/m at 40 psi , this provided a mere increase in horsepower from 25 hp from its normal 310 to 335 hp . This was injected into a multistaged axial compressor where the cooling effects, in what would normally be the hotter stages, made compression of the air easier , (and possibly increased mass flow marginally ??), giving the gasifier turbines an easier time , leaving more energy for the freepower turbines to extract .
My water injection experiments back in 1999 were inconclusive , there was a drop in TOTs but not any great change to thrust levels , possibly with some minor changes to fuel flows there could have been some , but certainly not 30% , maybe ~5%
I was injecting straight water at ~36:1 air/water ratio
Hope this helps
Cheers
John
kit Wallis who is a member of the GTBA showed me his engine working with water/meths injection aswell as normal kero being pumped into the engine at a GTBA efficiency competition a few years back, all he had was a simple pipe feeding near the intake of his home built engine and a pressure guage showing the increases it gave when allowed to flow into the engine.
from what Kit was saying you could almost turn off the fuel to the burners and the engine will run using fuel sucked into the intake, i think he mean't kerosene for this kind of running though.
the easiest way to test this is run an engine on kero and then let the engine such fuel via the intake and see any pressure or RPM rise, if theres a high enough rise turn off the pump and see if it sustains, an RPM drop will be seen when the pump is turned off for obvious reasons.
from what Kit was saying you could almost turn off the fuel to the burners and the engine will run using fuel sucked into the intake, i think he mean't kerosene for this kind of running though.
the easiest way to test this is run an engine on kero and then let the engine such fuel via the intake and see any pressure or RPM rise, if theres a high enough rise turn off the pump and see if it sustains, an RPM drop will be seen when the pump is turned off for obvious reasons.
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racketmotorman
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Hi Paul
Interesting you mention the injection fluid being "sucked up ".
My setup had a 5 litre container with a windscreen washer pump mounted in the bottom , the pump was wired thru a pressure switch set to cut in and out when comp discharge pressure ( P2 ) reached 30 psi .
The pump gave ~8psi with nil flow and about 1800 ml/min at full flow .
The water "squirted" thru ~10 fine holes in a length of 6mm ID nylon tubing wrapped around the FOD screen at the rate of ~1500 ml/min
During its first test run I notice water starting to dribble from the holes once the engine was running at ~15 psi P2 and continued to get worse at 20 psi and beyond, despite the tubing being some 4 inches from the comp face , there was certainly some serious "suction" going on :-))
By the time the pump cut in at 30 psi there was already a pretty good stream of water exiting each hole .
From the data gathered it was hard to differentiate when the pump came on .
The water injection was carried thru to the engines ,then max, P2 of 40 psi
I found all the hassles of pumps and containers of water just not worth it for the potential gains.
I have heard that straight methanol sprayed into the inlet of our small engines has made a difference to thrust , but no hard numbers were supplied unfortunately .
Cheers
John
Interesting you mention the injection fluid being "sucked up ".
My setup had a 5 litre container with a windscreen washer pump mounted in the bottom , the pump was wired thru a pressure switch set to cut in and out when comp discharge pressure ( P2 ) reached 30 psi .
The pump gave ~8psi with nil flow and about 1800 ml/min at full flow .
The water "squirted" thru ~10 fine holes in a length of 6mm ID nylon tubing wrapped around the FOD screen at the rate of ~1500 ml/min
During its first test run I notice water starting to dribble from the holes once the engine was running at ~15 psi P2 and continued to get worse at 20 psi and beyond, despite the tubing being some 4 inches from the comp face , there was certainly some serious "suction" going on :-))
By the time the pump cut in at 30 psi there was already a pretty good stream of water exiting each hole .
From the data gathered it was hard to differentiate when the pump came on .
The water injection was carried thru to the engines ,then max, P2 of 40 psi
I found all the hassles of pumps and containers of water just not worth it for the potential gains.
I have heard that straight methanol sprayed into the inlet of our small engines has made a difference to thrust , but no hard numbers were supplied unfortunately .
Cheers
John
John, i'm sure a simple servo operated on/off valve would work with the water/meths tube postioned at the outer face of the compressor intake, when the engines is running at say half throttle take a note of the engine pressure, RPM and temoperature then open the water/meths valve and see what increase it gives you.
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Irvine.J
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Compressor Injection
I had noticed at the shop the small windscreen washer pumps and can get quite large ones for as little as 10 bucks. I had planed to use one to try pumping some gasoline/diesel/kero into one of my chinese etc.
I hear though that they burn out real fast, anyone know if its true?
Also, you wont need a servo, simply a speed controller (more amps the better) with the power outputs directly onto contacts of the pump should work for water/meth control. All you need then is your reciever, a battery, and your TX. I'm gonna try it probably tomorrow let you know how I go, but if they burn out let me know.
I hear though that they burn out real fast, anyone know if its true?
Also, you wont need a servo, simply a speed controller (more amps the better) with the power outputs directly onto contacts of the pump should work for water/meth control. All you need then is your reciever, a battery, and your TX. I'm gonna try it probably tomorrow let you know how I go, but if they burn out let me know.
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Al Belli
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Washer pumps
Hi,
I have tried washer pumps on alcohol, and they work fine.
They fail instantly on gasoline !!!!!!
Al Belli
I have tried washer pumps on alcohol, and they work fine.
They fail instantly on gasoline !!!!!!
Al Belli
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Ash Powers
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Wouldn't it make more sense to inject just water into the turbine scroll near the inlet flange?? The water will absorb a bit of the heat, vaporize and expand, and add additional massflow through the engine. You could bump up the fuel flow as well to bring the TIT back up to where it was before the water injection, which should mean higher massflow with the same TIT, translating to more thrust?
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Irvine.J
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Washer pumps
Perhaps I should try Kero or Metholated spirits rather then gasoline then? Interesting that gasoline fry's them, I wonder why?
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Al Belli
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fuel pumps
Hi,
The rubber that the impeller is molded from is not resistant to gasoline, and softens due to the solvent effect.
Al Belli
The rubber that the impeller is molded from is not resistant to gasoline, and softens due to the solvent effect.
Al Belli
Gas/kerosene/glow fuel/water pump
Its not the fastest pump (just under 0.5 gal/min) and I don't know what kind of pressure it can produce, but its rated for just about all fuels out there.
http://www2.towerhobbies.com/cgi-bin/wt ... XDJR7&P=ML
Runs on 12V DC too, which I see as a bonus because I have a good 12V DC power source.
-Aaron
http://www2.towerhobbies.com/cgi-bin/wt ... XDJR7&P=ML
Runs on 12V DC too, which I see as a bonus because I have a good 12V DC power source.
-Aaron