Been a while - new project, T04 Gas Turbine.

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_Rahul_
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Post by _Rahul_ » Mon May 14, 2007 6:49 am

Mate .. one word description for that machine!
Awesome!!
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Ash Powers
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Post by Ash Powers » Mon May 14, 2007 11:29 pm

Well guys - today was the day of reckoning. :) I recieved the NTE2985 power transistors for the fuel pump controller and the repair went without incident. I mounted the transistor board to the back of the main casing for the electronics so it gets a good flow of cool air as the compressor draws it in.

I haven't done any static thrust testing on this engine at all so I was concerned as to whether or not the engine is producing enough to even make the scooter move under load, so I fired her up and spooled her to ~10psi and was impressed with the force, so I took her down the road for a test run.

With the thermocouple attached temporarily to my multimeter to get accurate TOT's, I was able to run her up to 15psi of case pressure until the TOT's were at 700C. The difference in thrust from 8psi to 15psi was considerable and really got the scooter moving along. I presume she topped out around 30-35MPH and could have gone faster with a little more distance. Regardless, I'm totally thrilled at this point.

Here's the video of the maiden voyage: please excuse my 6 year old acting like a nut. :)

11MB, so please be patient:
http://ashspecz.com/Image%20Gallery/Gas ... IM0627.AVI

I took her out for a second run and about a half mile down the road the TOT's shot up pretty high so I quickly shut her down. The walk back was grueling. Once I got back, I fired the engine back up again to find flames licking into the turbine and then proceeded to take her apart to see what's up.

Apparently 3 of the small hypodermic tubes that deliver fuel to the vaporizers had broken off and was dousing fuel all over the engine's core. A lot of this was making its way back along the outer casing and whipping into the turbine, causing the erratic flames I noted.

I am off to the hardware store to pickup some more O2 and MAPP gas so I can repair the injector ring and I have a slight modification to the injector ring I will be making to prevent this from happening again. I'll post more soon.

GOOD TIMES!!! :) :)

Jim Berquist
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scooter

Post by Jim Berquist » Tue May 15, 2007 2:05 am

It Runs! It Zooms! You Built it and it is so Cool.

The only thing Cooler then what you built was your little man in the Video runing down the road calling for his dad! Now That was Cool! Your teaching this little man things my father didn't have time for! Good for you!

jim
WHAT TO FRAP, IT WORKED![url=callto://james.a.berquist]Image[/url]

Rossco
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"He did a skid!"

Post by Rossco » Tue May 15, 2007 2:53 am

Hey Ash... Top work, right to the road!

Ha, your boy is a bit exited! The smoke on the turnaround and "He did a skid!"
Just wait till he "borrows the keys" to that one.

I got some new power toys to play with, ready when you are to publish your finals. Stress, flow and all.

Rossco
Big, fast, broke, fix it, bigger, better, faster...
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larry cottrill
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Very Nice, Indeed!

Post by larry cottrill » Tue May 15, 2007 12:27 pm

Ash -

Congratulations on a beautiful project - a really nice application. This is as close to a "practical" surface running (i.e. non-flying) jet project as anything we've seen for a while. Beautifully executed!

L Cottrill

Ash Powers
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Post by Ash Powers » Wed May 16, 2007 6:44 pm

Yesterday was quite a bit of fun - with the rebuild of the fuel injector ring, I added some 0.025" dia 316SS MIG wire "loops" to the end of the needles to help "fan" out the fuel stream coming out of the needles. The engine was running REALLY well and I was pushing 15psi P2 right at 700C TOTs. In a few short bursts I turned the fuel up and saw 20psi P2s and a notable increase in thrust, but the TOT's wanted to climb into the 750-780C regime so these were REALLY short bursts. :) In one top-speed run though, I tucked down on the scooter and was trucking somewhere around 45-50MPH at 15psi P2. :) It was awesome! :-O)

I rode the scooter around the neighborhood for several miles - we live in a very large neighborhood - spanning some 4 square miles with many very long and flat streets (nice for the fact I can also spread out the "piss-off" factor and avoid irritating my neighbors). After about the first 2 minutes, the engine cut out and I found myself walking back a LONG way - in looking over things, I reaized the fuel tank cap wasn't breathing and when I removed the cap, I heard a distinct suction and the top plate of the fuel tank visibly "bowed" back out when the vacuum was released, LOL. So I punched a breather hole in the tank cap and no more issues with that. After that was taken care of, I filled the tank almost to capacity and went on another joy ride. I probably ran the engine for 7-8 miles distance that time and on the way back, only about a block away from my house fortunately, the TOT's shot way up and I could hear a distinct change in the exhaust noise so I quickly shut her down.

I tore the engine back down to find that two of the new fuel ring injector needles had broken off!

I guess the 0.032" o.d. with a 0.025" i.d. is just too thin a sidewall for these tubes and while the engine is running the small vibrations coming from it must be causing them to flex to the point of fatigue and failure. The new ring I built had shorter needles and they weren't bent 90-degrees coming out of the main rail - they were a straight shot down to the vaporizer inlets. But the addition of the 0.025" MIG wire loops added mass to them which is likely what made them fail even sooner.

I have also noted some concerning amount of thermal warping of the combusion chamber outer liner. It is time to build a new one. I used 304SS when I constructed it and had later learned that 316 would be a better choice of materials to use. Last night I also inspected inside of the CC to see that the front plate is "wet" with oil/fuel which is telling me that I'm not getting as good of vaporization as I should have. I would expect the inside of the CC to be dry - it isn't, which is probably limiting the performance of the engine a good bit.

I came up with a new idea for the vaporizer tubes which should increase the vaporization ability of the fueling system: the vaporizer tubes will be straight tubes (which will benefit airflow) and they will be attached to the outer liner on the inside of the CC. This area appears to be subjected to a good bit of heat so using a bit of that to accelerate vaporization and act as "ribs" to help the CC hold its dimensions should be good. Given the issues I'm having with the hypodermic needle injectors, the fuel ring will reside around the outside of the outer liner, near the back of the engine. The openings for the vaporizer tubes will be in the side of the CC at the back as well. Instead of using hypodermic needles, the fuel ring will be filed at the entrance of each vaporizer tube and a small hole will be drilled using a 0.025" carbide drill bit.

Back when I was building the twin-turbo gas turbine, I built a fuel ring for the flame tubes in the same manner: I made a loop of 1/8" diameter SS tube around the top of the FT, filed "dimples" into the inner wall of the loop using a round file and drilled 0.025" holes that injected through 1/4" openings in the top of the FT. The fuel streams were all very consistent, however, in that initial design without vaporizers I did have problems with really high TOTs.

I will proabably go with 8 vaporizer tubes this time around vs. 6 that the engine has had up to this point to reduce the "load" on the vaporizer tubes - should be able to get much better vaporization and faster combustion. I will also purchase turbine oil rather than the 2-stroke oil I've been using - this 2-stroke oil produces a lot of carbon desposits..

I will also taper the combustion chamber's outer liner such that the front of the CC is a little smaller in diameter - this should improve the airflow around the outer liner. As it stands, I've questioned how much air is actually getting around the outer liner given the small annular space with the current CC. I will also be able to make the combustion chamber a little longer since there will no longer be a fuel rail at the front of the CC taking up space. It also looks like I'll be able to create a good recirculation zone at front of the CC with this layout as well - the previous J-tubes were probably generating a lot of losses and breaking up the recirculation zones. Here's the proposed revision:

Image

Rossco
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CFD

Post by Rossco » Wed May 16, 2007 10:15 pm

Hey Ash... Im nearly confident that i can get at least some intersting (possibly usefull) results for your layout from a little CFD on the sucker!

Its been a lot of work although i think i am ready to apply it to some more challenging projects, such as this.

Ill start a new model on the above picture, and we can make mods/changes and fix errors (on my part) as we go.

Rossco
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Rossco
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Renderings

Post by Rossco » Thu May 17, 2007 5:52 am

Hey Ash, started the build.
Need some info from you before i go any further.

Rossco
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Johansson
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Post by Johansson » Thu May 17, 2007 7:31 pm

Great progress Ash! It would be interesting to see some numbers on bike weight and engine thrust, it seems from the video that it puts out pretty much thrust for its size.

Have you considered to try a flow divider after the diffuser? I came across a norwegian homepage where the guy had some problems with high EGT and uneven combustion, and he fitted a lip to the exit of the diffuser that directs some of the air down towards the shaft tunnel. The page contains some temp figures that shows just how much there is to gain from such a simple modification. Might be worth a try?

http://home.online.no/~eikarlse/hybrid/ ... start.html

//Anders

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Jetbike roaring down the street

Post by Irvine.J » Fri May 18, 2007 12:09 am

That was excellent!
I'm very happy for you, so much time and effort to pay off in such a thrilling ride! It looked like you were really "Fangin" down the street there, good stuff man. Thats the sort of thing you could take to a motor show and get everyones head turning :D
James- Image KEEPING IT REAL SINCE 1982
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Ash Powers
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Post by Ash Powers » Fri May 18, 2007 12:29 am

Anders,

Wow - great find! I wish more people would be as thorough with their analyses as he was. He took the observation and formed a hypothesis as to what is occuring and made the modifications to the setup - followed by the testing and posting of the detailed info of his resuts. But the real question is how many other things did he do before discovering this or was it a matter of simply looking for a means of optimizing the performance of the engine? He presents the fix as a linear propogation that is a great read and easy to follow; a "one thing leads to another" appearance of the process. But what ultimately prompted him to tear into the engine was the fact the comp wheel was interfering with the inducer duct. Perhaps I'm just a moron when it comes to understanding cause-effect with a GT, but hey, if I never give up, then eventually I'll get it right, right? :-P

That area of my GT has always "bugged" me - in terms of the geometry of the parts of that area and visualizing how the air has to move through that area.... I know full well the benefits of a "smooth operation" and that area of the GT could definately use some attention! On the same note, I spent some 60 hours in the cylinder heads of my nissan 300ZX twinturbo with a die grinder/sanding drums; opening up the intake and exhaust ports as well as modifying the combustion chambers. Lots of work to improve the flow of air into and out of the CC... When I look at some of the design parameters of my engine, namely this section that also got your attention, I can see room for improvement - that link and description of the results is quite amazing.

Modified CC: note the removal of the plug boss and use of the shorter spark plug in the left cylinder to deshroud the valves at low lift. Also note the deshrouding around the periphery of the CC at the valve edges. FWIW: This is a V6 3.0L gasoline engine, twin-turbocharged, and it produces 693 horsepower at the rear wheels and 640ft/lbs of torque. It is one of the top-performing Nissan Z32's in the world in terms of balance of peak performance and low-mid RPM torque and power curve predictability. I've built 1000HP 300ZX's before, but unfortunately they are all top-end only and not much of that is useful power.
Image

Original CC:
Image

I know this isn't in the spirit of gas turbine engines but just an example of considering all the elements involved in an air-breathing type of engine.

Interestingly enough, I too am seeing signs of heat exposure at the back of the bearing tube and can see from the description in his page how a venturi/vacuum effect can cause a reversal of airflow through certain parts of the CC. If this is the same thing occuring in my engine then I'm a bit surprised - surprised in the fact that I had the impression that the annular space available between the CC outer liner and main casing was creating a bit of a restriction to flow.

This is the counter-intuitive nature of these engines... your eyes and mind can inadvertently fool you into a theory of what is going on due to overlooking one small factor involved in a particular process. Trying to make sense out of an observation has got to be taxing on the processing centers - I know it can make my head hurt!

I presume the best approach to determining the cause and solution to an issue in the GT is to kick it, shake it, yell at it, disembowel it and dont rule out even the smallest of effects that can play into the issue. It all sounds so easy to talk about it though.....

I will make up a plate like that GT has in it - that is an excellent idea and amazing how much of a benefit it produces.

A note to the members: pictures are worth a thousand words - post more pictures of your work!!!

Perhaps I'm missing something but is there any documentation of known issues and fixes that exist within these engines? Something along the lines of "if you see condition "x", then check the following and/or modify "x" parts."..

Some of the issues that you see in these engines can have counter-intuitive solutions to them so a resource like this may be useful to members trying to troubleshoot an engine build.

Either way, I love you Pulse-Jets! ;-)

Ash Powers
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Post by Ash Powers » Tue May 22, 2007 6:43 pm

I've spent a good bit of time yesterday redrawing all of the engine components and dimensioning everything. All of the parts have been drawn as seperate pieces so as to make keeping the drawing up to date much easier. To humor you engineering folks, I've been using Microsoft Paintbrush to create all of my drawings and building everything to scale on my Dell laptop's screen - using the screen with a pair of calipers to build the actual parts. :) Unfortunately without dimensions on the components, it makes for a difficult time of creating solid models in Solid Works.

Rossco has offered assistance in modeling the engine - his work is top-notch, he's a super-nice guy and is offering to create all of the solid models (with full rendering) as well as apply some CFD to it so we can get an idea of how the gases are making their way through the engine. You have seen some of his work already in this post as well as a few others - some beautifully rendered models of GTs and their parts.. :)

Here is the most current section drawing of the engine:
Image

The combustion chamber and outer casing aren't shown yet. We will go through setting up the CFD to analyze the airflow using the existing CC design to give us an idea of where the engine "was" before and see where we can make improvements in the new layout. I'm not so sure how well this approach will work out but I'm inclined to say it will at least give us a much better idea of how the gases are moving through the engine - given velocities, vectors, pressures, density, etc, if it works out as I envision, I think the end result will be far better than with the previous chamber design... Definately some exciting stuff! :)

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Post by Johansson » Tue May 22, 2007 7:30 pm

Those models that Rossco made are really nice, can´t wait to see one of the entire engine.

CFD? That is almost like cheating! :-)

How much have you choked down the jet pipe at the moment? 700C EGT is perhaps a bit high but with some combustor improvements it might even get close to 600C.

//Anders

Jim Berquist
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Red X photo's

Post by Jim Berquist » Tue May 22, 2007 7:34 pm

What's with all of the Red X photo's .........Is it my computer? Edit: Never mind it's me!!

Jim
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Ash Powers
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Post by Ash Powers » Tue May 22, 2007 8:07 pm

Johansson wrote:Those models that Rossco made are really nice, can´t wait to see one of the entire engine.

CFD? That is almost like cheating! :-)

How much have you choked down the jet pipe at the moment? 700C EGT is perhaps a bit high but with some combustor improvements it might even get close to 600C.

//Anders
LOL, yeah - it *should* make development easier but that's left to be determined - these engines are complex little buggers so it will be interesting to see how many hurdles we come across with applying CFD to it. However, modeling the actual combustion isn't so easy and certainly not absolute, so we will be left with trying to make an educated guess on what sorts of airflow around, into, and through the CC is "ideal". Hopefully we can gain some insight into modeling the current chamber as we have at least a couple of values to start with and then creating the new CC design from that info.

The jetpipe is a 2.75" pipe, tapered down to 2.41". From what I'm seeing in the current CC, there appears to be a good amount of improvement that can be made on the TOTs.

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