|
Post by andym on Mar 11, 2022 4:47:05 GMT -5
Hi Monty, I have done a large amount of testing with different spark plugs and “voltage generators” and I can confirm there is no need to use spark gaps. If you use a surface discharge plug (such as NGK BUE which are £2 each) you will have equivalent performance to an aircraft plug that is much more difficult and expensive to get hold of. Using just a microwave cap and (optional) Diode, you can put considerable energy through these plugs. The addition of a spark gap is effectively just increasing the breakdown voltage and therefore energy, it is equivalent to putting two spark plugs in series. Cheers Scott Hi Scott Sounds interesting.... have you tested this on an engine, well does it work once very wet, what spark rate did you get,
|
|
|
Post by andym on Mar 11, 2022 4:51:33 GMT -5
Just a quick update on the spark gap. I received a quote today. $1275 set up fee and $875 per unit. This for a 2 in long glass tube with a couple metal spheres and an alpha source.....Available from Alibaba for less than $200. I don't think I'll be using a spark gap! The rest of the components will be here Sunday. I did do some more testing. With the truck ignition coil, the best results are had by using a regular spark plug with the electrode cut off. The specialty plug looks impressive with sparks flying everywhere, but it doesn't ignite the WD40 as reliably. Surface gap seems to need more umph. I'll try to post some video of the plug testing when I get the new box put together and have some time. Monty Hi Monty Will you have a gas pre heat.... on this engine, if so you only need high voltage unit. I know John was able to light his engine on last test, lit it with the bang box, and not gas pre heat. Happy to send you spark gap, and plug for small fee and postage, All The best Andy
|
|
monty
Senior Member
Currently being spanked by mother nature.......
Joined: September 2018
Posts: 399
|
Post by monty on Mar 11, 2022 9:44:27 GMT -5
Andy,
No gas preheat. I want to start on straight jet fuel. I am putting together a combustion can test rig so I can try some things out before I risk burning down the entire engine. I'm really hoping I can use off the shelf readily available parts in the ignition system and avoid rare surplus things I have to scrounge for. I'm guessing spark plug placement is going to be important.
So far what I've learned:
IC engines need very high tension to create a spark under the immense compression they create. High boost makes this even more important. The amount of current required isn't that great though. Spark energies are in the neighborhood of 30-100 mJ.
Turbines need high current to be able to light cold kerosene in a driving rain storm. Combining high current and 60kV is a very dangerous thing, so the turbine ignition systems try to keep the voltage down to a few kV (still dangerous) and provide high current. The plugs have a semiconductor around the electrode to facilitate flash-over at the lower voltage, and then the capacitor provides the current through a choke to slow down the discharge time. Spark energies are in the neighborhood of 5-10 J.
I'm willing to sacrifice the ability to light cold kero in a driving rain storm since I'm not making a commercial FAA approved engine. As long as the engine starts under normal conditions I'll be happy.
I was thinking of splitting the difference. Using a longer slightly less powerful spark with higher voltage (15-20kV or so). This should negate the need for the specialized semiconductor plug. Some of the older engines used something like this. They had two electrodes and a long spark right across the fuel nozzle.
Testing a soaked plug with the ground electrode removed and an automotive coil gave consistent ignition of the WD40 spray. I'm going to try one of the high voltage units and some higher voltage ceramic caps and compare results to the microwave cap.
My understanding of the spark gap's function is to control the discharge of the capacitor so it's consistent under all conditions. What KV value are the spark gaps you are using? I was looking for 2kV because that is what the microwave capacitor is rated for.
I may be wasting my time. In which case I will gladly take you up on the offer!
Monty
|
|
|
Post by andym on Mar 11, 2022 16:57:05 GMT -5
Andy,
No gas preheat. I want to start on straight jet fuel. I am putting together a combustion can test rig so I can try some things out before I risk burning down the entire engine. I'm really hoping I can use off the shelf readily available parts in the ignition system and avoid rare surplus things I have to scrounge for. I'm guessing spark plug placement is going to be important.
So far what I've learned:
IC engines need very high tension to create a spark under the immense compression they create. High boost makes this even more important. The amount of current required isn't that great though. Spark energies are in the neighborhood of 30-100 mJ.
Turbines need high current to be able to light cold kerosene in a driving rain storm. Combining high current and 60kV is a very dangerous thing, so the turbine ignition systems try to keep the voltage down to a few kV (still dangerous) and provide high current. The plugs have a semiconductor around the electrode to facilitate flash-over at the lower voltage, and then the capacitor provides the current through a choke to slow down the discharge time. Spark energies are in the neighborhood of 5-10 J.
I'm willing to sacrifice the ability to light cold kero in a driving rain storm since I'm not making a commercial FAA approved engine. As long as the engine starts under normal conditions I'll be happy.
I was thinking of splitting the difference. Using a longer slightly less powerful spark with higher voltage (15-20kV or so). This should negate the need for the specialized semiconductor plug. Some of the older engines used something like this. They had two electrodes and a long spark right across the fuel nozzle.
Testing a soaked plug with the ground electrode removed and an automotive coil gave consistent ignition of the WD40 spray. I'm going to try one of the high voltage units and some higher voltage ceramic caps and compare results to the microwave cap.
My understanding of the spark gap's function is to control the discharge of the capacitor so it's consistent under all conditions. What KV value are the spark gaps you are using? I was looking for 2kV because that is what the microwave capacitor is rated for.
I may be wasting my time. In which case I will gladly take you up on the offer!
Monty
Let me know when or if you need parts..... but yes try other things first.... the aircraft plugs work better when wet with fuel
|
|
|
Post by madpatty on May 3, 2022 8:24:42 GMT -5
Calculated the turbine exducer flow area in as accurate a way as I know how....
First I carefully carved a piece of card stock that would fit between the blades:
Then I traced it on graph paper, took a photo, imported it into Rhino and scaled it to the same grid size as the paper. After that I created a surface using splines and measured the area.
The magic program tells me 0.8311 sqin/passage. There are 11 total passages yielding 9.142 sqin of flow area in the exducer!!!
Needless to say I was happy with this number Hi Monty. Did you ever measure the exhaust tip angle on these turbine wheels? Seems like there's quite a bit of factory clipping on these turbine wheels which may effect their power producing capability. The exducer throat area is also quite bigger than the similar Garrett G trim wheel. Thanks.
|
|
monty
Senior Member
Currently being spanked by mother nature.......
Joined: September 2018
Posts: 399
|
Post by monty on May 3, 2022 19:34:42 GMT -5
Hi Monty. Did you ever measure the exhaust tip angle on these turbine wheels? Seems like there's quite a bit of factory clipping on these turbine wheels which may effect their power producing capability. The exducer throat area is also quite bigger than the similar Garrett G trim wheel. Thanks. Nope, never did. It varies root to tip. All I really cared about was choke flow and areas. I know the mass flow, pressure ratio, and efficiency thanks to John and others working with this turbine in the past. That's all I really needed to verify the cycle design, so I didn't pursue it further. It's not something I can change anyway. I may get more interested when I start testing the engine. Now that I've discovered a foundry that can cast inconel for reasonable prices within a couple hrs drive! They can go from a 3D print directly to an investment casting. I may look at a custom turbine. One step at a time though.
I've got the ignition system designed. I'm just waiting on an 11/16-24 UNEF tap....who knew such a thing existed!? Apparently, Bendix used this odd ball thread on all the magneto leads and plugs back in the day. A self inflicted wound using old aviation stuff, but it works well in this instance.
I've also got the combustion can, fuel manifold, air swirlers, and fuel pump designed. I've started ordering material to make all the stuff.
I've also got the forms for all the castings printed. Weather has been cold, wet and rainy. No chance to cast anything. Hopefully I'll make really good progress this summer.
|
|
|
Post by wannabebuilderuk on May 6, 2022 11:38:10 GMT -5
"11/16-24 UNEF tap....who knew such a thing existed!?"
Not surprised when oil burner nozzles are usually 9/16-24 unef lol
|
|
monty
Senior Member
Currently being spanked by mother nature.......
Joined: September 2018
Posts: 399
|
Post by monty on May 22, 2022 12:26:08 GMT -5
Hi guys,
I've been meaning to get this video about my ignition put together for a while. Finally got around to it. Hope there is some good info in there for people wanting to build an ignition.
odysee.com/@ProfessorMonty:1/Ignition:0
Monty
|
|
monty
Senior Member
Currently being spanked by mother nature.......
Joined: September 2018
Posts: 399
|
Post by monty on May 22, 2022 13:25:48 GMT -5
If anybody has tips on how to embed video....I'm all ears.
Monty
|
|
|
Post by andym on May 22, 2022 16:13:54 GMT -5
Hi guys,
I've been meaning to get this video about my ignition put together for a while. Finally got around to it. Hope there is some good info in there for people wanting to build an ignition.
odysee.com/@ProfessorMonty:1/Ignition:0
Monty
Nice.... only worry would be the long electrodes getting melted off ? but works well.... as for how to post video in comment window click on icon that looks like clapper board , its in the tool bar above, hover over it and it will say insert video
|
|
monty
Senior Member
Currently being spanked by mother nature.......
Joined: September 2018
Posts: 399
|
Post by monty on May 22, 2022 17:08:44 GMT -5
Andy,
I tried the video embed icon, but couldn't get it to work.
Melting the electrode is a possibility. If it's a problem, I plan to cut the ground off, and use a vented sleeve electrode like some of the older high voltage air gap igniters. I'm just copying the older stuff. Hopefully I won't have to though.
Monty
|
|
dieselguy86
Veteran Member
Joined: September 2014
Posts: 186
|
Post by dieselguy86 on May 22, 2022 17:45:25 GMT -5
I bought the champion 589 plug, looks to be the same electrode end as yours, but has a regular end on the top for a regular sparkplug wire. Just to let others know in case they want to use automotive stuff.
|
|
|
Post by wannabebuilderuk on May 23, 2022 4:47:01 GMT -5
Hi guys,
I've been meaning to get this video about my ignition put together for a while. Finally got around to it. Hope there is some good info in there for people wanting to build an ignition.
odysee.com/@ProfessorMonty:1/Ignition:0
Monty
Monty, The hv module with a thick lead is used in negative ion generator, the thick lead is the negative. Your setup is similar to mine/andyms/jetrics setup except we use spark gaps and hv diodes to charge the microwave capacitor and one/two 6/12v stun gun modules, I use this type - www.ebay.co.uk/itm/265020980736Decided that 1.4s between each spark wouldn't be good enough to guarantee ignition without a puddle of fuel (do not want to experience a runaway) so now it fires at 0.4s 😁 gfycat.com/fortunatecelebratedcoquiFinished the bang box cable, looking very professional if I do say so myself. Uses the core of a mig welding torch which is just a long wire spiral with insulation so it conducts plus is flexible android easy to connect both ends. Stainless steel braid is from a 22mm female to 15mm compression sink connection as you can't seem to buy it anywhere cheaply.
|
|
monty
Senior Member
Currently being spanked by mother nature.......
Joined: September 2018
Posts: 399
|
Post by monty on May 23, 2022 6:43:45 GMT -5
Monty, The hv module with a thick lead is used in negative ion generator, the thick lead is the negative. Your setup is similar to mine/andyms/jetrics setup except we use spark gaps and hv diodes to charge the microwave capacitor and one/two 6/12v stun gun modules, I use this type - www.ebay.co.uk/itm/265020980736You scared me to death!! thinking I'd been holding onto a 11kV thing....but then I thought that CAN'T be! I'd have felt that!!! So I checked with a meter and the small lead is definitely ground. The thick lead is the positive. Here is the link.
If the specs can be trusted (doubtful) they do seem to confirm that the thicker output lead is the positive and the small white lead is ground. I also noticed the unit I'm using only puts out 11kV, but the current is 1 amp. The unit you are using is 30kV but the amperage is only .4-.6.
If the spark gaps had been more readily available, I probably would have done what you guys are doing. I just wanted to use readily available off the shelf stuff in case I want to make a few more. I'm approaching this more as a product development effort and less of a hobby/one off thing.
Monty
|
|
|
Post by wannabebuilderuk on May 23, 2022 7:08:22 GMT -5
Monty, The hv module with a thick lead is used in negative ion generator, the thick lead is the negative. Your setup is similar to mine/andyms/jetrics setup except we use spark gaps and hv diodes to charge the microwave capacitor and one/two 6/12v stun gun modules, I use this type - www.ebay.co.uk/itm/265020980736You scared me to death!! thinking I'd been holding onto a 11kV thing....but then I thought that CAN'T be! I'd have felt that!!! So I checked with a meter and the small lead is definitely ground. The thick lead is the positive. Here is the link.
If the specs can be trusted (doubtful) they do seem to confirm that the thicker output lead is the positive and the small white lead is ground. I also noticed the unit I'm using only puts out 11kV, but the current is 1 amp. The unit you are using is 30kV but the amperage is only .4-.6.
If the spark gaps had been more readily available, I probably would have done what you guys are doing. I just wanted to use readily available off the shelf stuff in case I want to make a few more. I'm approaching this more as a product development effort and less of a hobby/one off thing.
Monty
Previously on one I had it said the negative was the thick lead since they say its a negative ion generator, guess it depends on who makes them/correct data.
|
|