Micro distributor leakage

[sition]

I made a distributor for my v4, only 20mm in diameter. When the distributor is not installed on the v4, it will not leak electricity. When the cylinder is under pressure, it will leak. The gap is about 0.1mm. What is the reason for this?

I use the igniter of the motorcycle, it seems that the speed is not enough to make the v4 reach 5000 rpm and the power is off.

 

[tornitore45]

I made a distributor for my v4, only 20mm in diameter. When the distributor is not installed on the v4, it will not leak electricity.

How do you energize the distributor without the engine? depending on the set up the distributor hanging in mid air without engine, wires and plugs may be capable to hold a million volts without "leaking".

When the cylinder is under pressure, it will leak.

Leak? Jump a spark? from where to where.

One thing to know is that sparking voltage increase with pressure, so when the cylinder is in compression a spark may prefer an air gap outside the engine as soon as the voltage reach the lower level required at atmospheric pressure.

I use the igniter of the motorcycle, it seems that the speed is not enough to make the v4 reach 5000 rpm and the power is off.

That last sentence make no sense at all. The speed of what? If the power is off what is the test trying to accomplish? The V4 will never reach any RPM with the power off. A V4 engine running at 5000RPM requires as many Sparks/second as a single cylinder engine running at 20,000 RPM, not many motorcycle igniter can deliver sparks that fast.

The gap is 0.1mm. Assume that is the gap from rotor to plug contact inside the distributor.
That is unnecessarily too small, tolerance alone may make it crash.
A 20 mm diameter distributor is very difficult to make to keep electrical rigidity to the 8 to 10 kV involved. Some serious design consideration must be given to prevent sparks inside the distributor to jump to the wrong spot.

 

[BaronJ]

Hi there, the cylinder pressure raises the voltage to one that the plug will fire at, so where the distributor will not leak at normal atmospheric pressure, it does in use under cylinder pressure.

 

[BaronJ]

FWIW Electricity will jump approximately 1000 volts per mm !
I.e 10Kv will jump 10 mm.

 

[TonyM]

Hi there, the cylinder pressure raises the voltage to one that the plug will fire at, so where the distributor will not leak at normal atmospheric pressure, it does in use under cylinder pressure.

And herein lies the problem with miniaturising ignition components. From the humble spark plug to distributors and magnetos. The higher the compression ratio the worse it gets.
As baron says, The spark will jump 1mm per 1000 volts in air. It will also take the path of least resistance. A compression ratio of 10 to 1 means around 10 atmospheres of pressure so the spark will prefer to jump a 2mm gap at atmospheric pressure than a 0.2 mm gap at 10bar. This is not scientifically accurate as the fuel density makes a difference too but you get the idea. That's why it is difficult to make accurate scale models of those old stubby spark plugs work in a recessed head. The solution is maximum insulation and larger air gaps where insulation is not possible.

 

[BaronJ]

Hi Guys,

Many years ago, in a previous life, I designed ignition units for single cylinder speedway motor cycles. The much higher than normal compression ratios caused all sorts of electrical leakage problems, even using standard motor ignition components. The biggest advantage was getting rid of the contact breaker.

 

[sition]

How do you energize the distributor without the engine? depending on the set up the distributor hanging in mid air without engine, wires and plugs may be capable to hold a million volts without "leaking".


Leak? Jump a spark? from where to where.

One thing to know is that sparking voltage increase with pressure, so when the cylinder is in compression a spark may prefer an air gap outside the engine as soon as the voltage reach the lower level required at atmospheric pressure.



That last sentence make no sense at all. The speed of what? If the power is off what is the test trying to accomplish? The V4 will never reach any RPM with the power off. A V4 engine running at 5000RPM requires as many Sparks/second as a single cylinder engine running at 20,000 RPM, not many motorcycle igniter can deliver sparks that fast.

The gap is 0.1mm. Assume that is the gap from rotor to plug contact inside the distributor.
That is unnecessarily too small, tolerance alone may make it crash.
A 20 mm diameter distributor is very difficult to make to keep electrical rigidity to the 8 to 10 kV involved. Some serious design consideration must be given to prevent sparks inside the distributor to jump to the wrong spot.

thank you. Your answer gave me a lot of help.

 

[sition]

And herein lies the problem with miniaturising ignition components. From the humble spark plug to distributors and magnetos. The higher the compression ratio the worse it gets.
As baron says, The spark will jump 1mm per 1000 volts in air. It will also take the path of least resistance. A compression ratio of 10 to 1 means around 10 atmospheres of pressure so the spark will prefer to jump a 2mm gap at atmospheric pressure than a 0.2 mm gap at 10bar. This is not scientifically accurate as the fuel density makes a difference too but you get the idea. That's why it is difficult to make accurate scale models of those old stubby spark plugs work in a recessed head. The solution is maximum insulation and larger air gaps where insulation is not possible.

Thank you for answering my question. Because the engine is too small, the distributor can only do 20mm, can you reduce the contact size to open the distance?

 

[sition]

Hi Guys,

Many years ago, in a previous life, I designed ignition units for single cylinder speedway motor cycles. The much higher than normal compression ratios caused all sorts of electrical leakage problems, even using standard motor ignition components. The biggest advantage was getting rid of the contact breaker.

I have a RC four-cylinder cdi but the size is a bit big, because I am going to put the v4 on the rc model car, the size is bothering me.

 

[tornitore45]

There are other ways. Eliminate the distributor. Google "Wasted spark Ignition".
You may start here: https://en.wikipedia.org/wiki/Wasted_spark
There is more.
You can use two ignitions. http://www.cncengines.com/
Driven by two sensors

Move the distribution function to the primary and use four coils.
A single HV source is applied to all 4 coils. 1 magnet, 4 sensors, each sensor's output enables only one coil to be energized by completing the circuit to GND.
Just an idea I do not know it this was ever done before.

 

[BaronJ]

Hi Siton,

Any chance of some pictures of your distributor ?

 

[editor123]

Having two distributors and two ignition systems can cause a problem because of cross-talk between the electronic ignition systems.
A friend tried two distributors with separate electronic modules but that caused a great deal of cross-talk and the engine would never start for that and a few other reasons.
He switched it to two of the ignition modules designed by Dave Sage and John Geddi that are very resistant to cross-talk. You can see the engine run at . The article on building the ignition module is in issue #34 of Model Engine Builder magazine.

You could set up a distributor to simply trigger four ignition modules. and leave all of the secondary ignition setups separate. Those Ford Coil-Over-Plug modules work very well and cost about $5 each on e-Bay. You just drive them with a 12-volt pulse and they do the rest.
I'm writing an article on 4, 6, & 8 cylinder distributors for the next issue of the magazine but to ensure of little if any cross-talk in the secondary side, the contacts are about one-half inch apart or more.
Don't forget to vent the distributor or you may find that it will spark over because of gas generated during the unavoidable spark between the rotor and the secondary contact.

BTW, I am 3D printing everything but the metal contacts and the 'stem' of the distributor. Even the spark plug and Distributor post boots are printed in a flexible material.

As they say, you cannot scale electricity or gas/air molecules.

 

[sition]

 

[BaronJ]

Hi Sition,

Nice engine ! With regard to your distributor issue. Even if you could fix the distributor electrodes on a 20 mm circle you would only have 15 mm between them assuming the feeds were of zero size. I don't see the rotor arm with its collector as too much of a problem. You could get away with two mm wide electrodes and good insulation. One that will resist tracking, because that burning will allow leakage that can only get worse.

Pictures of your distributor would help.

 

[sition]

Hi Sition,

Nice engine ! With regard to your distributor issue. Even if you could fix the distributor electrodes on a 20 mm circle you would only have 15 mm between them assuming the feeds were of zero size. I don't see the rotor arm with its collector as too much of a problem. You could get away with two mm wide electrodes and good insulation. One that will resist tracking, because that burning will allow leakage that can only get worse.

Pictures of your distributor would help.

Thank you. I reduced the electrode to 1mm and the pointer to 1mm according to your instructions. There is no leakage now. Thank you. Later, I'll send up pictures of my distributor.