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OT - Help with spark plugs and coils please


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As a couple of you know, I am in the process of building a jet engine, based on a turbocharger. This is mainly to try to improve my absolutely terrible fabrication skills. I am nearly there, and have built the burner tube, forcing cone and all of the connections to the turbocharger. The bit that I have to sort out next is the ignition circuit. For this, I have bought a spark plug, normal vehicle coil, ignition lead, and car battery.

The coil has 3 terminals on it - one for the spark plug, then a couple more for power. They are labeled with the polarity. I have connected a lead from the negative terminal of the battery to the negative terminal of the coil, and to the body of the spark plug. I then connected a lead to the +ve terminal of the coil, and tapped it onto the +ve terminal of the battery (which is fully charged, btw). There is a spark, but it is incredibly weak - I would have thought that I would be able to get a nice yellow, warm spark from it.

The question is, when I have been looking for circuit diagrams for an automatic device to make the spark (based on a 555 timer - I have no problems building that part), quite a few of the diagrams show the coil as having an incorrect polarity (ie. the wrong way around)

Does this seem like the correct thing to do? Will the spark get hotter if I switch it faster (like 1KHz) or will it just flicker more?

Any help much appreciated.

Cheers, Keir.

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Have a look here!

Nice & easy 556 based. The second circuit, which is a simple capacitive discharge will likely give a better spark.

Depending upon the required frequency of the sparks, how about just using a starter from a gas cooker? These produce a decent spark, generally about twice a second. Look out for a cooker dumped by the side of the road - that's where my last one came from!

Si

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Will the spark get hotter if I switch it faster (like 1KHz) or will it just flicker more?

It's not frequency, it's energy, for that you need to have the coil duty cycle (dwell in engine terms) such that the coil is as charged as possible before you fire it. There will be a frequency at which you get the most "full" sparks per second which I would think (without getting the crayons out) would give the best results.

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As a couple of you know, I am in the process of building a jet engine, based on a turbocharger. This is mainly to try to improve my absolutely terrible fabrication skills. I am nearly there, and have built the burner tube, forcing cone and all of the connections to the turbocharger. The bit that I have to sort out next is the ignition circuit. For this, I have bought a spark plug, normal vehicle coil, ignition lead, and car battery.

The coil has 3 terminals on it - one for the spark plug, then a couple more for power. They are labeled with the polarity. I have connected a lead from the negative terminal of the battery to the negative terminal of the coil, and to the body of the spark plug. I then connected a lead to the +ve terminal of the coil, and tapped it onto the +ve terminal of the battery (which is fully charged, btw). There is a spark, but it is incredibly weak - I would have thought that I would be able to get a nice yellow, warm spark from it.

The question is, when I have been looking for circuit diagrams for an automatic device to make the spark (based on a 555 timer - I have no problems building that part), quite a few of the diagrams show the coil as having an incorrect polarity (ie. the wrong way around)

Does this seem like the correct thing to do? Will the spark get hotter if I switch it faster (like 1KHz) or will it just flicker more?

Any help much appreciated.

Cheers, Keir.

Keir,

I would be interested to see some photo's off your project when it is done as I am starting to collect parts to make one myself ;)

Cheers,

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Will post up photos soon. The difficult bit is getting the burner tube made, and connected to the turbocharger - it depends on what design you go for.

The only bits that I have bought are:

1. turbocharger - could be from anything, so long as the bearings are reasonable. Mine was given to me by John (Turbocharger)'s dad. It's from a 6.25 litre TD truck engine.

2. oil pump. I got a 12 volt one from e-bay. Very similar to This one but they come up a bit cheaper than that every now and again

3. Spark plug, lead and coil - the bit that i'm trying to sort out at the moment.

Lots of off cuts of steel - plate and tube.

I decided to go for propane, rather than diesel. This is because it doesn't need pumping to rediculous pressures - just attach a regulator and pipework, and off you go. I used a piece of copper tube for the injector nozzle, so that I could adjust it as needed. The first time I had a go, I got a very long, thin flame - not good for this application. If you want a diesel injector nozzle, I have loads - could post a couple if you wanted.

I tested the burner tube this evening. With just propane, it burns VERY rich - a yellow, sooty flame. As soon as I attach a leaf blower to the side and get the mixture right, it really roars.

The next thing for me it to make a steel box section frame to mount it all in, then sort the oil tank out. I'm going to use an offcut of steel tube and plate over the ends. voila - one oil tank.

Once that is done, I can attach the turbocharger and create some NOISE. My neighbor hates me anyway. I think that he wants a nice, quiet person living next door. What he has is a grubby bloke with a dirty land rover outside. Most of the tarmac on my drive has melted from where the diesel tank split. I keep chickens (noisy in the morning), and will have a jet engine running in the back garden.

Put it like that and I wouldn't want to live next door to me, either.

Thanks for the advice.

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Are you building a pulse jet not a jet engine? There is a guy in New Zealand that specialises in them, you might want to have a peek there. Google for "$1000 cruise missile pulse jet"

Now, I don't know if this is true, but be aware that building a pulse jet in the UK might make you run into a few legal issues as I don't think you are allowed to, mainly coz they are a great platform to then create your own cruise missile (like the NZ guy) and the possible danger of a high speed device in the hands of any loon. This is second hand info from a chap I work with who made drones for the navy to test anti missile missiles with many years ago when I mentioned that I was considering making a pulse jet out of curiosity.

Having said all that, where are the bloody pictures, always fancied two small pulse jets on on each side of the defender to scare the pants off someone on the motorway! :)

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Nope - a true jet, not a pulse jet.

This one uses a turbocharger as a compressor - the only difference between a homemade jet engine and one that you would see on an airliner, apart from size, is that the gasses go straight through in those, whearas in mine, there are various turns for the gas - just to get it through the turbocharger takes a 90 degree turn. That means that there is very little thrust - just massive amounts of hot air, and loads of hot air.

A pulse jet is simply a tube, with a venturi in the middle - a fuel inlet in the narrow point of the venturi, and then a single piece flap valve to keep the air going the correct way. You really need a normal jet engine to get them going, so might have a go at one when this project is finished. You have to remember that the only reason for this project (apart from annoying the neighbors and cooking the chickens) is to improve my absolutely awful fabrication skills.

Pulse jets are not illegal to make, own or use - just good fun. No law has ever been able to hold back the march of technology. If you want one, give it a go.

Photos later today, when Mrs TM gets home - at the moment it is a 2 person job to get the flame going, plus another person to take the photos. Hopefully, it should soon be a little easier to get going - i'm not sure whether to use the leaf blower to get it going, as I do now, or to try to put a compressed air starter on there - difficult to get right, but easier to use if I do.

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Hmmm not sure what I am going to fuel mine on as yet but if I go for the diesel option I might well take you up on the nozzle offer ;)

It could also be handy to see how you have constructed your combustion chamber! I have a 52page pdf file here regarding construction/running ect! (can e-mail you a copy if you want one) & it goes on about makeing the combustion chamber relative to the turbo's inducer diameter & square inch area ect :huh:

As far as ignition goes I have got a ignitor plug from a "propper" jet engine I intend to use & depending on what fuel I use I have a turbine controller box that controls when different things switch in during starting!

As for starting I am thinking of going down the compressed air option just because I have that & don't own a leaf blower :)

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