Will this simple Piezo circuit work?

Thread Starter

David Nolan

Joined Aug 4, 2021
30
Hi guys,

Just wondering if this simple circuit will work as I expect it to. So this is for an engine, I'm utilizing multiple Piezo igniters to create a spark plug and I'm trying to figure out if this will work. I understand that this would be pretty easy to test I just don't have the components right now and I'm clueless when it comes to circuitry. So there might be something like 50 igniters, they will be triggered separately, one at a time. What I want to happen is that the piezo's won't interact with one another, they will jump the gap in this configuration, firing the engine and the charge won't be sapped by vibrating the other crystals. In this hypothethical circuit, one terminal of the piezo igniter is connected to a common contact like in the picture and the other terminal of the Piezo's is connected to the other contact. Am I correct in assuming that the electrons will choose to jump the gap instead of vibrating the other crystals? Or am I incorrect?

Thanks in advance for any input.

- David.


Ignition Circuit.png
 

LowQCab

Joined Nov 6, 2012
1,343
Unfortunately, your cool idea won't work.

As the density of the Air increases in the Spark-Gap,
the Voltage required to Ionize the Air in the Gap increases.

The Compression-Ratio of the Engine that You are dealing with
will be the largest determining factor.

When the Air in the Cylinder is compressed,
it has the effect of increasing the required Voltage to jump the gap.

Most modern Engines have a Compression-Ratio of around ~10 to 1, and up to ~12 to 1.
This means that the Voltage must be at least ~10-times what it would be at atmospheric pressure.
In other words, the Gap gets ~10-times larger under Compression.
.
.
.
 

MisterBill2

Joined Jan 23, 2018
9,844
If you can get the system to jump a half inch in air it should work in an engine. If you can get a quarter inch spark in air it might work. The challenge is stressing the multiple pieze elements at exactly the dame times..
 

Sensacell

Joined Jun 19, 2012
2,919
The problem is that Piezos are basically capacitors electrically.
You have 5 of them in parallel in this circuit, assuming one is mechanically struck, the resulting voltage will be absorbed by the remaining 4 units, dramatically reducing the voltage.

The other 4 will also react mechanically, the piezo effect is reciprocal, which will consume the energy and reduce the voltage as well.
 

Yaakov

Joined Jan 27, 2019
3,755
A little poking around puts the number of lifetime cycles for a piezo igniter (not a piezo actuator) at ~35K.

I can't easily confirm this as all the data sheets with clear lifecycle tests are actuators, but if it is even off by 10 times, it makes this moot. I would strongly suggest contacting a manufacturer and getting good data on the number of cycles any prospective device is capable of...
 

Thread Starter

David Nolan

Joined Aug 4, 2021
30
Unfortunately, your cool idea won't work.

As the density of the Air increases in the Spark-Gap,
the Voltage required to Ionize the Air in the Gap increases.

The Compression-Ratio of the Engine that You are dealing with
will be the largest determining factor.

When the Air in the Cylinder is compressed,
it has the effect of increasing the required Voltage to jump the gap.

Most modern Engines have a Compression-Ratio of around ~10 to 1, and up to ~12 to 1.
This means that the Voltage must be at least ~10-times what it would be at atmospheric pressure.
In other words, the Gap gets ~10-times larger under Compression.
.
.
.

I didn't consider the compression ratio... I think I best stick to more regular ignition methods. It's a damn shame though.
 

Thread Starter

David Nolan

Joined Aug 4, 2021
30
A series arrangement could work, the challenge will be the insulation.
If piezo ignition would work easily then we would see it in use. But it is an interesting concept.

I would have thought, a series connection would certainly not work. I used parrallel because I thought it would cause the Piezo's to choose to jump the gap first to complete the circuit with the least resistance instead of going through another crystal (Which I didn't want) then having to jump the gap also to complete the circuit. In series the charge would have to go through all the crystals before it jumped the gap, sapping all the energy for sure. Am I incorrect in this understanding?
 

MisterBill2

Joined Jan 23, 2018
9,844
the other concern was the lifetime of the piezo devices. If 35,000 operations is correct, that would be used up in a short time of running. I have no idea as to the validity of that lifetime statement, but it is worth examining. In a normal application as a spark lighter it would probably never be reached, while in an engine it would be reached quickly.
 
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