Got a "Napier Gazelle" but need help

[TwoGears]

I'll do my best tomorrow whe I'm back home.
I have a pretty small milling machine. When I'm very careful I can smoothen the female-contact pretty good.
The male one, as said by ernie, isn't really a problem.

You're roght... there is nothing to loose

If everything will be well, I'll do further tests and even a start attempt on friday.

[TwoGears]

Here are the results...

I cleaned any contact along the high-voltage line of the ignition system.
Afterwards i started some tests by connecting any igniter to any exciter-box --> same results.
Since I have nothing to lose I heated the igniter with the higher insulation resistance
and got almost 1MOhms as the resistance between inner-electrode and outer case.
Connected again and... same results: Just a few sparks, then nothing for a while, then again a few sparks

The resistance should be okay. If you ask me it's better to have a very high insulation-resistance
because the spark has to leap over at the ends of the electrode anyways.

So I had a better look at the non working electrode while firing. And there I saw why
it stopps sometimes. It's not because it doesn't fire anymore or due to a high resistance. The problem is
that the spark doesn't take its usual way through the air. Sometimes the spark manages to find a
way through the outer part of the insulation material. I saw some very weak sparks wandering along the
surface of the insulation material instead of breaking through the air.

This can mean two things:
1.) The exciter-box is damaged and produces less voltage than needed. But with the other electrode
mounted on this exciter there is no problem with firing (yet). And the high-resistance electrode mounted
to the other exciter ends with no firing at all (but there were small smoke trails coming out so I suppose
the sparks jump through the insulation material)

2.) The igniter is damaged or to be more accurate, the insulation material at the tip of the electrode doesn't
allow a spark through the air anymore.

What are your thoughts upon this?


Possible solutions:

• New igniters (hard to get if there are even any replacements out there)
• Building new igniters by my own (i researched a little bit and I think it's possible, but hard work)
• Trying to attach a nib to the tip of the electrode like at car igniters (to lead the spark)

[Deleted]

me and my friend make these if you want one

youtu.be/SI22x8DMHqk

john has one and can tell how well they work

[racket]

Hi Andy

They're scary beasts , especially when fired off in a darkened room to unsuspecting "victims" ;-)

Cheers
John

[TwoGears]

Is it the complete system with exciter-box and the igniter electrodes?

[cursorkeys]

On my Williams plug the problem was that the metal had ablated so far that it couldn't reliably ionise. I was seeing arcing at the connector as well when the plug failed to fire, something has to give eventually in the HT circuit.

I considered very carefully turning the end down in the lathe to restore the geometry. A local machinist suggested 'C2 Carbide' inserts would be suitable for the job. I would guess you'd need to feed incredibly carefully to avoid cracking the insulator. As you saw, I just got a replacement plug in the end and the box worked reliably with that then after.

As an alternative to Andy's box there is also a nice little flyback ignition exciter design on the web: www.technologie-entwicklung.de/Gasturbines/Bangbox/bangbox.html
I built one using a standard ETD34 core for the flyback and a tiny ETD11 for the boost, both with N27 ferite. It was downright frightening with a microwave oven capacitor

[Deleted]

Nov 11, 2013 5:43:26 GMT -5 TwoGears said:

Is it the complete system with exciter-box and the igniter electrodes?

Can Send Plugs, but dont know if they would fit your engine

[TwoGears]

Nov 11, 2013 12:42:02 GMT -5 andym said:

Can Send Plugs, but dont know if they would fit your engine

I'll go and take the measures tomorrow. then we can check if you've
got some of them. Hopefully 

Otherwise I've got some ideas to solve the problem:

1. High temperature ignition systems
       + They sell long electrodes
       - Very expensive (even just the electrodes)
   
   
2. Build it by myself with ceramic cement 
       + Price is okay
       + Should be simple to build
       - High temperature capability without burning them in a 2000°C oven
       - Material availability
       - Unknown parameters
   
   
3. Simply insert some kind of car spark-plug into the old case
       + Inexpensive
       + Material is easy to get (if you have old electrodes like I do)
       + Known parameters
       - Difficult to build
       - Spark-plug needs to be machine to fit the old case
       ? High temperature durability (should be okay)
   
   
4. Replace them with self-made torch igniter
       + Price is okay
       - Very difficult to build
       - Also need fuel for them (and some kind of control system)
   
   

I have several more ideas but those are the most promising ones.
What do you think?

However, I'd prefer to get replacements instead of constructing them by myself 
If anyone has some secret contacts involved in old turbines, please ask them if
they can get their hands on replacement igniters.

andym
As said above, I'll measure mine and post the dimensions here. Thanks for your offer so far.

cursorkeys
I think it's the same problem as you mentioned. They're simply shot.
Since I still don't have anything to lose I'll build one of those bangboxes (a little modified)
and try if I get more suitable sparks out of the old igniter-electrodes until
I've found a replacement.

racket
My heart nearly stopped when I fired mine outside the turbine case the first time 

[ernie wrenn]

I built a ignition system using a Motorola Ignition Vibrator and a couple of automobile ignition coils. Vibrate the - negative side. Works great.

eBay item number:261188630146

This one is $30 .. I have used OLD vibrators out of tube type radios,, just as good but hard to find.

[TwoGears]

It took me a while to measure the igniter spark plugs and draw a proper draft.
Sorry for the delay though.

Draft: Igniter Electrode.pdf (78 KB)

The spark plugs type also says: K.L.G SRR 101/1

andym
Do you have something similar andy?


At the moment I'm listing the parts I need for a new exciter-box.
I think ebay would be the best source for me to get those kind of capacitors.
I even have a spare ignition coil from my old car around.
What kind of material are these spark plugs made of? Especially the outer electrode tube.
I think the only problem is the long shaft my spark plugs have. Otherwise I could use some
ordinary spark plugs.

[Deleted]

Hi... the plugs i have are not like this, but you may well be able to mod them to fit, if you pm me i mite be able to give yu parts list for parts, but when i last looked one part is no longer listed :-( i do have some spare but very limited, i know a friend has some, but he may want them for bang box's he is making

[gidge348]

Hello Two Gears, just wondering how the project is going?

I just had a look at your drawing of the Igniter plug and realised it looks as though a RR Nimbus plug could be modified to fit.



It is 12mm dia and I think all you would need to make is the nut?

I bought mine from cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=130987354429

Regards

Ian...

[TwoGears]

Hello again!
Spring is comming and the temperatures get warmer and warmer here,
so it's about time to wake the engine from its hibernation during winter

I thought a lot about the igniter plugs and also made up some ideas.
However, it seems the automatic post notification mail didn't reach me,
otherwise I'd also have thought about using those plugs which Ian
posted a picture off.

gidge348
Thanks for the infromation Ian.
The UK site of eBay seems to be down somehow at the moment. Could you please
make a picture from the top side of the plug (where the exciter is connected to)?

Just machining a nut would be way more easy to make than my idea.
At the moment I'm making a blueprint of my plug construction, but there
are three points which I don't have any clue about.

• I've measured the thread on the plug to be g24 3/16 7/32 but I don't have
  any clue what this could mean. Is there any standardised thread label which
  would fit those measures?
  
  
• Common car spark plugs (just the core without the outer metal thread) are about
  12mm in diameter. That's a problem because it could be hard to shrink the diameter
  since I think ceramics are bad for precessing via lathe.
  Are there any thinner ones?
  
  
• Which material are aviation spark plugs usually made of? And how thick should
  the outer wall be to not melt in the combustion chamber?

Those are the problems I have on my DIY spark plug design at the moment.

I'd also consider to use those from a RR-Nimbus as suggested by Ian. If somebody

has some of them lying around at the moment

I'm looking forward to get her to run again soon.
I'm sure with the help of you all I'd be able to do so

[gidge348]

I don't know how you have measured the threads, but the numbers "g24 3/16 7/32", I think (G24) would refer to 24 TPI (threads per inch) and a diameter of 3/16 inch & 7/32 inch.?? otherwise known as UNC in that size.

Look up this en.wikipedia.org/wiki/Unified_Thread_Standard and match the diameter of the nut to these sizes. As the size of nut gets bigger and the same 24 TPI applies they become a UNF and a UNEF. Hope this makes sense

I will get a pic of the plug for you later and post ..... Sorry I only have 2 as spares and they are like rocking horse sh+t so want to keep them.


Ian...

[TwoGears]

Back from the land of silence... 

Well, in the meantime I did a lot of research about the plugs and ignition systems.
As I wanted the enging to run again as soon as possible I tried to grind the igniter plugs
until the destroyed semiconductor material has been removed.

First it seemed to work properly when I switched on the exciter boxes with one of the
igniter plugs ganging in free air. Then I did the same grinding work on the other one.
When I put them back into the engine one didn't work from the start so I removed it.
Then the other one stopped too.
Now both are free to air and don't work in any way. not a single spark. I did some wipes
with a fine sandpaper over one of them which made one single spark afterwards but again,
nothing.

I have four ideas on this case for now:

1. Since I did grinding on them in a way that in the end there is a plane geometry at the
   tips there is the possibility that the gab between the inner and outer electrode is to big.
2. The current is hitting through the igniter system somewhere else. However I can't see
   where since it was at least working on one of the igniter plugs continously before I
   put them back into the engine.
3. There is a connection failure somewhere in the path between the igniter plugs electrodes
   and the exciter box.
4. The exciter boxes are damaged. However, they sound the same as they did back then when
   I did my first start attempts and until the igniter plugs were damaged.

For 3) and 4) the possibility that both exciter boxes have the same problem is pretty low. At least
one should work.

Any ideas there?

...those were the bad news, now the good ones will follow...

On the top of all, I was able to obtain a almost complete manual for the engine with a lot
of information and drawings. They are like a holy grail to me now, I think most of you can
understand 

After breaking my head about the igniter plugs and many nights of constructing alternative
plugs I finally found an easy way to replace mine. Although I'm not sure about their specs.
and how they would behave in a turbine.
What I thought of are Glow plugs which usually are used in diesel engines. There are
two types of them. The ceramic and the metal glow plugs. As those will have
their place in direct line to the turbine blades I'd prefer the ceramic ones. This has one
major reason: damage prevention!
In case the tip of the glow plug breaks due to the strain there is a high risk on damaging
the blades. As ceramic is very brittle it will be crushed to pieces while flying through
and it's more likely the blades won't have any damage than in the case where a piece of a
metal glow plug flies through (don't want to think of it).

It definitely is possible since they reach temperatures of more than 1200°C and can stand
high temperatures over a long time.

And again I need your thoughts and ideas


Edit...
Here is a picture where you can see the original(right) and the ground(left) spark plug.