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NT/5 TurboJET
Objectives:
NT/5 is our most advanced turbocharger turbine to date. With better funding and a lot more experience, we were able to take our experimental turbine project to the next level. Project Chronology:November 29I've finally got the new turbo, it has a huge (4" inducer)
compressor and looks great. I have also ordered a banner
fiber optic sensor that will be used to measure turbine speed. December 05 We bench fired the original NT/4 reverse flow, swirl combustor. We used a gas powered leaf blower to blow air into the air casing and burned propane gas to roughly simulate combustor operation. With no turbine mounted, we can observe the flame directly by looking up the flame tube. When we connect a second 100lb propane tank and crank it, the combustor roars with the flame extending 12" past the end of the opening! The air blast (observed by standing 12 ft behind the combustor outlet) quadruples over the blast produced by the blower alone with no flame, and it gets real hot too! Since the combustor pressure during this simulation is only about 15
psia, and normal pressure is up to 30psia, we have concluded that the flame shape and
characteristics observed are not likely to be representative of actual operation,
therefore we need windows in the air casing to observe the flame during actual turbine operation.
We're learning, slowly. I pressure tested a combustor flame observation window today using double clear glass cutting goggle lenses mounted in a 1 1/2" pipe union. The glass burst at about 100 psia. I will try again with a piece of solid 1/4" glass from the local glass shop. We have about 3 hours running time on the combustor now and have learned a great deal! I tried varying the amount of combustion air holes around the fuel injector and found that the best looking flame (less holes in the primary zone) lights and looks great, but produces a hot spot on one side of the flame tube. When we add holes, the flame is harder to light, pops into a rose bud shape almost immediately, but does not produce any hot spots. We're not sure how to proceed at this point.
December 10 The 3D solid model of the NT/5 project is going well. The solid model allows us to visualize placement of components and by having a virtual model of the engine, components and test cell (stand), We can work on the layout easily. December 15 I finally got the Banner fiber optic sensor, hooked it up with a nine volt battery and
spun a piece of 1.25" dia. cardboard with four black pie shaped marks on it in a
Dremel tool (another one of Springer's ideas). I had to switch to high speed mode (50
microsecond response) and was able to register 1,800 Hz on my Beckman Circuit mate
DVM,
this works out to 27,000 rpm. The slowest no load speed was 13,350 rpm, the rating on the
tool says adjustable from 5,000 - 30,000 rpm. they lie! The Banner D12SP6FPY sensor works
great and appears to be the correct choice as far as I am concerned, I spent hours farting
around with my own design before I could afford this device. December 23 Here is a view of the thrust measuring engine mount sub-system. The turbine housing and
the combustor will sandwich the red 3/8 thick mounting plate, the entire jet will be
hanging off the side of the pivot shaft. Thrust acting through a 6" moment arm (the
turbine housing) will produce a torque in the pivot shaft, this torque will act through
the long 20" moment arm to produce a force that can be measured by the 50 lb.
electronic load cell at the bottom. The entire engine mount sub-system is being made of
laser cut type 304 stainless steel. Pivot shaft rotation and jet movement are expected to
be imperceptible. I spoke to an engineer at Kendall Lubricants, he says the best oil to use in my jet is Synthetic 5W 30 motor oil. Apparently this oil is relatively thin when cold, (it has a low viscosity index) this will reduce drag and really help at start-up. 5W 30 oil is thinner than the 15W40 Diesel oil I have been using, so I'm hoping it will lower EGT. Synthetic oils are very high quality lubricants that should generally do a better job all around and are a better conductors of heat than regular oils. He also said that ATF and turbine oils are not suitable for automotive turbo chargers for various reasons. December 28 We have now run about 6 hours of experiments and test burns with the combustor and leaf
blower. It seems to work best with all the back wall air holes around the IIM plugged,
(with window putty). The flame lights easily, even with the leaf blower at full throttle,
the flame rotates nicely in the center of the flame tube and there are no hot spots even
with both 100 pounders cranked. I have determined that the air casing to flame tube joint
must be re-worked because it leaks like mad due to thermal expansion, this means we will
also have to rearrange the IIM (injector/igniter module) mounting. The results were impressive, at lower air flows and fuel settings, the flame appears as a rotating cigar shaped blue region floating nicely in the center of the flame tube. (see photo below) At full throttle on the leaf blower and with more propane flow, the flame pops into a "rose bud" shape and touches the flame tube walls, although no hot spots appear.
I have spent several hours re-working the air casing to flame tube joint and the IIM
tube. The air casing is now secured with a stainless steel flex-clamp. The air seal is
maintained by a 45 degree taper seat machined on both halves of the joint. I made both
flanges on a lathe from mechanical tube and heli-arced one onto the air casing and one on
top of the old flange on the flame tube. (I had to cut the old flange and about an inch of
material off the bottom of the air casing. I test fired the combustor with the new air casing to flame tube seal and the new IIM tube today. The flame lights easily and forms a tapered corkscrew shape at any blower speed. The flame stays in a corkscrew shape and does not touch the flame tube walls at all! Even with both propane tanks wide open. At first I was happy to see this, but then I realized, because of the lack of jet blast and the nasty odor, that the fuel is not burning completely and the flame is not burning up in the primary zone where it should be. I think more air is needed in the primary zone. The next step is to make a sight glass so we can see what's happening. Then we need to
drill some primary air holes in the back wall around the IIM. We will need to make some
kind of adjustable collar to allow us to quickly adjust the area of the air holes during
testing. Not one but two sight glasses are now installed in the air casing. One looking up
towards the turbine, and one looking down towards the fuel injector. I used 1/4"
thick boiler sight glasses, these are designed for high temperature and fit on the end of
a piece of 1-1/2" pipe with a big union nut. I had to elongate one of the dilution
air holes to provide a better view of the flame, so I elongated all four holes around the
flame tube at that point so as to keep things symmetrical. I also drilled a pattern of
3/16" and 1/8" holes around the IIM on the back wall of the flame tube, we will
continue to use window putty to temporarily block selected holes during combustor testing. Today I made a high performance air eductor to replace the leaf blower during combustor testing. This device is basically a 3" dia by 8" long venturi with a 3/8" high pressure nozzle in the center. The nozzle is connected to our main air line in the shop (we have a 50HP compressor) with twin 1/2" air lines and is controlled by a 3/4" ball valve. With the valve full open, tons of air is drawn into the intake producing a gale force wind out the exhaust and a deafening roar. This noisy little thing greatly out performs the 3HP leaf blower, I'm dying to try running the combustor with it.
SHOCKWAVE CITY!!!
Today I made
my first Tiger Stripe Shockwave! We ran the combustor on shop air directly, the eductor
did not produce the desired pressure, so we just took the 3/4" air valve and
connected it to the combustor air tube. We clamped a piece of 1/2" steel plate with a
3/4" hole punched in it over the exhaust flange to simulate the pressure drop caused
by the turbine. With the air on full and no flame, the combustor air pressure was about 8
PSI, with both fuel valves at full blast the pressure jumped to 20 psi and a 18 inch long
striped shock wave blasted from the hole. The sound is deafening, my brother counted 8
mach diamonds in the jet exhaust, YES!!! The 14ga. and 3/16" thick LASER cut stainless pieces for the engine mount subsystem finally arrived today. The parts look great! I hope to TIG weld everything together, at least the main beam for the load cell, tomorrow.
The engine mount subsystem is finished and the air intake Assy. with start air injector and fiber optic probe is nearly done. I expect to run NT/5 for the first time within the next few days if all goes well. I have started planning the free shaft turbine and speed reducer portion of the project. I sent this document to several gear manufacturers on the web, but no one seems to have much to offer.
February 12 The NT/5 TurboJet ran for the first time today after work. The jet starts easy but much work is needed. I will post more details later. Click to hear NT/5 spool-up! February 14 I ran NT/5 again today after work. The engine mounting sub-system is barely visible in this photo.
NT/5 TurboJet
(ready to run for the first time). Since starting NT/5 for the first time, we have made several changes. - changed the oil
from 15W40 diesel to 5W30 synthetic, this produced an increase in cranking speed from
about 100 rpm with cold 15W40 to 6,000 rpm with slightly warm 5W30 at 50 psi. - increased
the oil supply line from #4 to #6, getting quite a pressure drop across the hose with the
cold 15W40. - re-curved the air impingement nozzle so it points more in the direction of
rotation, this made a big improvement in cranking speed. - hooked up the tach sensor to a
frequency counter, have to multiply the readings by 60 to get rpm, but otherwise it works
great! We are now ready to refine the design by methodically making changes and recording
our observations. Phil and I were finally able to get NT/5 to rock a little after several hours of experimental work on the primary zone air holes. The compressor is big, possibly too big. We installed a huge 1" ID ball valve in the compressor discharge to act as an air bleed. We can run 15 psi at 41,000 rpm with the air bleed wide open and blasting like crazy. I can't wait to pipe this bypass air into the tail pipe for after burning! We are having a hard time to get adequate fuel pressure from the propane tanks in the
cold weather. I have ordered a K cylinder of hydrogen, we'll see how it works on the
weekend. Here is a photo of a Caterpillar diesel turbocompounding system I saw in a magazine.
The turbo has a separate free shaft power turbine that helps drive the crank through a
geared drive shaft. This type of free shaft turbine is exactly what we are looking for to
extract power from NT/5. I believe the turbo is made by a company called COMPREX A.G. in
Sweden, but I'm not sure. I would like very much to acquire one of these units, please
e-mail me if you have any info on this company. Our experiment with hydrogen was a success! Max readings were 49,000
rpm. 22psi, about 35 lbs. thrust, 1,200f EGT, with both propane and hydrogen together. We
emptied the hydrogen cylinder in about 10 minutes. Best results to date with NT/5! It
would have gone faster but the exhaust nozzle blew off, that caused the compressor to
surge which blew the intake screen off. We fixed all that then blew the compressor hose
off. Then the intake air bent the tach probe down and the tach stopped working. After all
that we were out of hydrogen, so we hooked the both propane tanks back up an it still
worked great, I'm not sure why its not flaming out anymore, but it looks like it will run
well, as is, with propane. As long as we can get enough propane pressure we don't need the
hydrogen. Still lots of little bugs to work out before I will worry about making any
thrust. Adequate fuel supply is still a problem. Today, after a brief consultation with Tim Arfons, I decided to
make the change to jet fuel. I purchased a couple of different sized oil burner nozzles
from the local heating supply house, we will use a Detroit diesel fuel pump driven by a 0
- 2,800 rpm drill to supply straight kerosene (Jet A). We will do some experiments with
the pump and nozzles to see how they work together. Bench tested the fuel injection system today after work. We are using a large Detroit diesel fuel pump (3/8 gears), 5 gph 60 deg semi solid oil burner nozzle, 2,800rpm drill. We were able to make well over 200 psi at the nozzle after disabling the pressure relief valve in the pump. Atomization is good at moderate to high flows, dribbles a bit at low flow. I love the smell of burning jet fuel, can't wait to try it in NT/5.
My brother Steve gave me a hand running NT/5 on Saturday after work. I spent a couple of hours making a stainless support strut for the fiber optic probe unfortunately the probe did not survive the Heli-Arc welding despite my best efforts. We ended up cutting the plastic fibers and zip tying them to the side of the probe, this worked great. The fuel supply is not such a problem in the warm weather, after leaving both propane cylinders in the sun for a while, the vapor pressure was up to about 115psi. We had an excellent run-up, max speed 54,000 rpm, 18 psi, and enough thrust through the 2 3/4" nozzle to move the entire rig. For the first time, we had to worry about the whole works taking off across the shop floor. I wanted to see if we could start NT/5 by allowing propane to issue from a torch, directly into the intake screen. We motored the compressor wheel with the start air, turned on the ignition and opened the propane valve... nothing happened, so I partly closed the start air valve to reduce the cranking speed and tried again. There was a huge EXPLOSION and the exhaust nozzle went flying backwards off the tail pipe (I was expecting a "hard start" so we weren't totally surprised), but the explosion ignited the propane which resulted in a FIRE that melted the zip ties and the probe. (We did not expect fire at the torch tip) I fixed up the probe and cleaned up the mess and were
back in business, but then the jet wouldn't run right, it would flame out at about 20,000
rpm. I had not bothered to reinstall the exhaust nozzle because it was too hot to handle.
So we stuck the nozzle back on and presto! everything worked great. The only limiting
factor at this point is fuel flow. Next I will try propane directly from the cylinder with
no regulators, just the shutoff valve. This should make NT/5 rock! (Kids, don't try this
at home!)
I made-up a pair of these Propane Delivery Adapters. They consist of a propane tank fitting on one end, a gauge (not really needed) and a Harris regulator outlet bushing/check valve on the other end. We connect the fuel hoses to the outlet checks and blow propane vapor directly into the combustor, unregulated. These work really great, we ran 58,000 rpm @ 15 psi. Unfortunately with all this extra power available we fried the turbine. We saw sparks issue from the jetpipe, I quickly shut both fuel valves, but it was too late, the tips of the turbine blades all have little chunks ripped out from centrifugal force. (You can see it happen on the NT/5 Video) I will have to take the turbo to our supplier for a check-up and a new turbine. We machined the exhaust nozzle out from 2.75" to 3.0" to
reduce the EGT and then did another run-up (still with the damaged turbine). We clocked
61,200 rpm @ 18 psi with so much thrust that a plywood blinder screen that we use in our
shop was blown over from 75 ft away! Best yet for NT/5, and that's with a fried turbine! Were
happy now! I took the turbo in to our Turbo Supplier today, they will replace the turbine and bearings. We expect to be back on-line in about two weeks, this time running on Jet-A. We have a new operating rule; From now-on we will not increase the fuel flow when the pyrometer is pegged at 1500°F!
I got the turbo back, it's as good as new. The fried turbine is worse than I thought. The tips of the blades have all ripped off. You can see exactly where the oil leaves the shaft, its burnt blue beyond that point. I have painted the compressor wheel nut half black and half white with GM® touch-up paint, this should improve the sensing range of the tachometer. A visit to SEW Eurodrive in Mississauga proved interesting. The people there were friendly and quite helpful, they have some cool 10:1 planetary speed reducers. They are working on a couple of ideas for a speed reducer that we could use to drive a generator with our proposed free shaft turbine.
Finally some progress! We now have the A/R 1.70 turbine housing we've been waiting for. With a full range of housings we hope to learn about the effects of turbine A/R on performance. I am hoping the A/R 1.70 housing will yield better results with the big compressor, it should allow a higher flow of gasses to pass through the turbine without producing more turbine speed. The housings look the same at first but they are very different. Notice
how fat the gas passage is on the 1.70, the passage leans away from the center of rotation
on the 1.70, straight up (tangential) the 1.50 and in slightly on the 1.14. The 1.14 and
1.70 housings are brand new and have never been on a diesel. (There are detail shots of
the housings from all angles on the NT Infopack CD) WOW! 71,000 rpm, WHAT A BLAST! With two one hundred pounders of propane wide open (no regulators) NT/5 absolutely shrieks! At these speeds everybody runs for cover, its wild. The 1.70 A/R turbine housing works great! We were able to hold steady at 66,000 rpm, 1350egt, 25psig. Here's what we observed:
Next test run will be with the new 90mm nozzle.
I bored the existing exhaust nozzle out to 85mm and did another series of test runs today after work. The manager at Speedy muffler was kind enough to expand the air delivery tube for a better fit-up to the compressor hose. A pair of big 3.5" rad hose clamps from Kenworth eliminated any further worry about the hose slipping off under pressure. At 51,000rpm, EGT was 1300° F compressor 15psi, with little or no surging. Increasing fuel flow would cause the compressor to surge right through to 66,000rpm 1350° F with the pressure gauge fluttering between 17 and 22 psi. Opening the air bleed tends to reduce the surging, decrease the rpm and increase the EGT. With the exhaust nozzle removed the engine would flame out at about 25,500rpm for some reason, it ran right up to 72,000rpm with no nozzle yesterday, what gives? I had the entire turbine housing red hot for the first time today. A spark shot out of the jet pipe during a high power blast and I thought the worst, but on tear-down we couldn't find any damage, the turbine tips are still like new and the flame tube looks great. (probably a June bug) The sound this thing makes is incredible! I stood back and removed my ear muffs to see what NT/5 really sounds like. Even at 50,000rpm (I won't leave the controls at higher speeds) the sound is like a shop air gun being blasted right beside your ear, its an intense spraying or rushing sound. You can't hear the whine from the turbine or the oil pump motor at all. And to think we have yet to build an after burner, I can't wait!
I have added four 20mm holes and four 20 X 25mm ovals in the dilution zone hopping to reduce EGT slightly. And we have rigged up a slick new dilution zone water injection system. (this is where it's going to get real interesting) Here are some scans of what we have been up to lately. (AutoCAD drawings of all this stuff are included in the NT/5 Infopac).
The extra holes in the dilution zone were very effective! NT/5 no longer flames out with the exhaust nozzle removed and the EGT at 30,000rpm is down to around 850° F (was 1300). The extra holes worked so well, we will add more. The size and placement of our flame tube air holes were based on pictures of commercial jet engine combustors. We realize now that since our compressor is producing relatively low air pressure, (30psig as opposed to say 175psig or more in a commercial turbine) we need much larger holes. The water injection was a partial success. As predicted by a couple of friends on the dtt list, the nozzle placement we chose was not appropriate. We thought the three 0.062" streams of water injected before the turbine would flash to steam instantly. We were wrong, we actually had liquid water bubbling out of the combustor to turbine housing gasket. Opening the water valve at high power increased rpm and lowered EGT somewhat but not the way it should have. We will use a hollow cone spray nozzle aimed at the compressor air intake next time. I hooked-up a pressure switch and a big red warning light for the oil system to indicate low oil pressure. This takes a load of my mind when running NT/5. We also tilted the instrument panel up for easier viewing. Installing 1/4 turn ball valves on the fuel delivery adapters has made throttling much easier.
We have hooked up a meter for the thrust load-cell and will be measuring thrust on every run from now on. Here is the data from this weekend:
With the new turbine housing, the extra dilution holes and the water injection, we are no longer able to get enough fuel from the propane tanks to achieve redline. (75,000rpm) We really need to get the jet fuel system working now.
My brother Steve gave me a hand again today after work. We were quite relaxed because we have the NT/5 apparatus fairly well sorted-out now. We can spend more time playing with NT/5 and learning its operating characteristics without worrying about oil pressure and engine speed etc. NT/5 is very easy to start and spool up. It still flames-out periodically on propane but always re-lights easily. We did some low speed runs and found we could run as slow as 15,000 rpm @ 700°F steady. By adding fuel slowly we could spool right back up to full speed without excessive EGT. The compressor surges at all speeds above around 36,000 rpm. With the air bleed full open, the surging is reduced, but not eliminated. Even at 72,000 rpm @ 25 psig the compressor is still surging. Tomorrow we will install a T18A40 compressor wheel and housing.
Today I replaced the huge T18A90 compressor with a more normal T18A40. We found NT/5 harder to start and spool-up with the smaller compressor, but the surge was almost totally eliminated and NT/5 seams to sound and run better in general. We still get the occasional flame-out. Pressure as a function of EGT was much higher. The compressor slaps right over to 30 psig as soon as N1 reaches around 60,000 rpm. I'm sure we could get 35 or 40 psi at 75,000 rpm, but we did not have sufficient fuel pressure to go faster. We could only get about 50 lbs of thrust @ 60,000rpm - 1,400°F with the 80mm nozzle today. (we've got to get that jet fuel system working soon!)
And
now for the good stuff.
January 31 I finally got a chance to build and run a proper After-Burner. I used a oil furnace nozzle rated for 9.5 gal/min @ 100 psi, we pushed straight kerosene through it at 350psi with a Detroit Diesel fuel pump turned by a 3/8 electric drill. At low turbine speeds the afterburner produces a big lazy yellow flame. As N1 speed increases, the flame gets smaller and more intense.
We will continue to update and improve this page
as the NT/5 project progresses and as time permits.
Want to know more? Please send your comments & suggestions to:
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Here is a lo-res sample of what's on the NT/5 video: 
