Water Sparkplug

[aljhoa]

Deflagration and Detonation

Hi all,

I stumbled upon this topic and noticed the ubiquitous argument involving rapid expansion vs explosion.

In an internal combustion engine there is NO explosion. There is the oxidation of a 'fuel' that has a flame front and finite speed of propagation. It is a fast rate but still finite ... it is nothing more than a rapid burning .. and more specifically the flame or wave front is subsonic. And besides, the point is to heat the air volume in the cylinder to produce a change in pressure. This kind of 'burning' has a rather disappointing name ... "deflagration". This is in contrast to (what most people would call an explosion) a "detonation". The wave front here moves at supersonic speeds.

In a reaction engine (jets, most rockets) you have deflagration ... just a rapid heating, expansion and acceleration of a mass to produce thrust. But research has produced much improved performance from fuels by implementing techniques that 'detonate' the fuels resulting in the production of a more efficient form of supersonic wave thrust ... the 'Pulse Detonation Engine' ... again not to be confused with pulse jets and ramjets ... which are deflagration engines NOT detonation engines.

For a more tangible illustration see this video:
YouTube - The Audible Difference between Deflagration and Detonation

Attempts have also been made to apply detonation principles to the engines that have a mechanical output ... like a car or truck engine. There are and will be many hurdles for these applications but they're tryin':

See a Pulse Detonation Turbine Truck Engine here:
YouTube - Turbine Truck Engines' Hydrogen Powered Pulse Detonation Engine

... apples and oranges literally,

Greg

Detonation is the term sometimes erroneously used to describe engine pinging under load,
often caused by faulty exhaust gas recirculation (EGR)system (e.g. carbon buildup plugging one or both ports), misfiring (e.g. bad sparkplug) or pre ignition caused by hot spots on the piston.
Popular theory was that colliding flame fronts caused "detonation" as it was observed on the test engine having see-thru-cylinder head for taking high-speed pictures.
On older engines with CR=10.5 adding water or retarding the timing closer to TDC (i.e. lowering combustion temperature) helped to reduce "detonation".
Al

[gmeast]

Detonation is the term sometimes used to describe engine pinging under load,
often caused by faulty exhaust gas recirculation (EGR)system (e.g. carbon buildup plugging one or both ports), misfiring (e.g. bad sparkplug) or pre ignition caused by hot spots on the piston.
Popular theory was that colliding flame fronts caused detonation as it was observed on the test engine having see-thru-cylinder head for taking high-speed pictures.
On older engines with CR=10.5 adding water or advancing the timing helped to reduce detonation.
Al

Well, that's the 'LOW TECH" definition of 'detonation'. The scientific, technical and engineering definition is as I have stated it above. 'detonation', 'run-on', 'self ignition', 'auto-ignition', 'pinging' and some rather inaccurate versions are expressions of the of the same thing which is quite different than "detonation" as it applies to what I was referring to in my post.

By the way, in a perfectly tuned and clean engine, 'pinging' can merely be caused by an insufficient fuel octane rating where simply the heat from compression causes the fuel-air mixture to 'pre-ignite' in the combustion chamber prior to TDC ... the opposite of a 'cetane' rating or 'cetane number' (sort of) which is something you want in a diesel fuel ... you want self-ignition ... which works great there because fuel isn't introduced until the right time (after compression but can be slightly before TDC as with the modern high performance diesel HP common rail fueling systems).

[Aaron]

Fabrication and testing of an enhanced ignition system to reduce cold-start emissions

Fabrication and testing of an enhanced ignition system to reduce cold-start emissions in an ethanol (E85) light-duty truck engine: G.P. Gardiner

14 mb document including plug modification for plasma with tungsten.

Information Bridge: DOE Scientific and Technical Information - Sponsored by OSTI

[dingo]

Has anyone used an off the shelf CDI and simply add a diode from coil
primary to high voltage? It would be the same as the single cap plasma
circuit and should work fine. Most would have about a 4uf cap at 400v.
That is the most common I've seen - at least in that range.

I have a few CDI's but haven't tried that yet but if it works the same,
would be the easiest for anyone to do without having to build a circuit.

A booster cap system could be added at anytime later in parallel with the
plug.

have you had success with the CDI idea ? could you sketch out how i would do that....as well as adding the booster cap... I have afew CDI units i could try it on.

Thx
D

[Aaron]

using off the shelf cdi

Dingo,

I haven't tried an off the shelf cdi with diode.

Basically, I'd just hook up a cdi and to test it, put a diode with the anode
on the ignition coil primary + and put the cathode of the diode to the
HV output. This is for normal positive polarity HV.

I don't know if a single HV diode or string will hold up but it would be good
enough to test to see if there is plasma at the plug. There is no reason it
shouldn't be. That is all these homemade circuits are - cdi with the diodes.

You could have mutliple diode strings going from the coil primary to each
plug for actually running an engine.

Greg, anyone, any comments on this?

[dingo]

Dingo,

I haven't tried an off the shelf cdi with diode.

Basically, I'd just hook up a cdi and to test it, put a diode with the anode
on the ignition coil primary + and put the cathode of the diode to the
HV output. This is for normal positive polarity HV.

I don't know if a single HV diode or string will hold up but it would be good
enough to test to see if there is plasma at the plug. There is no reason it
shouldn't be. That is all these homemade circuits are - cdi with the diodes.

You could have mutliple diode strings going from the coil primary to each
plug for actually running an engine.

Greg, anyone, any comments on this?

But, the CDI output at plug is much higher than the standard 20K V...isnt it ? (since 200 +V goes into Primary)....so would the microwave diodes hold up to that?
(dont want to fry good cdi units)

[Slovenia]

Thank You

Fabrication and testing of an enhanced ignition system to reduce cold-start emissions in an ethanol (E85) light-duty truck engine: G.P. Gardiner

14 mb document including plug modification for plasma with tungsten.

Information Bridge: DOE Scientific and Technical Information - Sponsored by OSTI

Aaron,

Thanks very much for sharing this link!!

Best Regards,
Slovenia

[Aaron]

diodes

But, the CDI output at plug is much higher than the standard 20K V...isnt it ? (since 200 +V goes into Primary)....so would the microwave diodes hold up to that?
(dont want to fry good cdi units)

Most of the cdi schematics i've seen have 400v 2-4uf dumping to the primary.

I would use strings of diodes made of 6A100's - those are cheap and rugged
diodes rated at 6 amps 1000v each. There are others that Greg, etc... can
tell you work good. Just to test, just one diode string is needed to be placed
as indicated and then manually trigger the cdi. I don't see why it wouldn't
work. I have about 3 non-labeled cdi's so I can't look up the specs but
I'll try it on them when I have time.

[Aaron]

plasma ignitors

Aaron,

Thanks very much for sharing this link!!

Best Regards,
Slovenia

Your welcome. There aren't too many docs discussing modifications of
off the shelf plugs and turning them into tungsten plasma ignitors.

[Kinetix]

Aaron, I did such an experiment, using a classic CDI schematic (home made). I added a diodes string from the CDI capacitor to the spark plug. And it did make plasma. The problem that may occur is about connecting the ignition coil. It doesn't work both ways, as I recall.
This was only an experiment, and never mounted on car. But I don't see much problems with that.
Anyway, you cannot put a second capacitor paralel to the spark plug, as it would have to deal with the HV. You have to put the HV diodes between the cap and the spark plug.
dingo, the amount of voltage developed by the ignition coil depends on the lenght of the air gap that has to be jumped. It's about the spark plug gap. If you keep it small enough, you would probably run your car with 10-15kV in the ignition HV circuit. The HV develops only until the voltage is able to jump the gap. After that, the voltage drops.
Cheers.

[Aaron]

plasma ignition

Anyway, you cannot put a second capacitor paralel to the spark plug, as it would have to deal with the HV. You have to put the HV diodes between the cap and the spark plug.

Glad it worked because it should have.

Without special plugs, booster caps probably aren't desirable because
they'll kill your plugs quick anyway so for a bare minimum plasma ignition,
the 400v 4uf or so cap in the cdi is probably sufficient. I would use Greg's
same setup except you'd be using an off the shelf cdi. Not sure if he
knows of any issues you might run into with that.

You can find surface gap plugs without resistors off the shelf. That is what
I would use without having access to the Firestorm replications or otherwise.
You could always cut off the ground strap from some non-resistor plugs
but I'd rather just buy them that way.

[dingo]

Aaron, I did such an experiment, using a classic CDI schematic (home made). I added a diodes string from the CDI capacitor to the spark plug. And it did make plasma. The problem that may occur is about connecting the ignition coil. It doesn't work both ways, as I recall.

dingo, the amount of voltage developed by the ignition coil depends on the lenght of the air gap that has to be jumped. It's about the spark plug gap. If you keep it small enough, you would probably run your car with 10-15kV in the ignition HV circuit. The HV develops only until the voltage is able to jump the gap. After that, the voltage drops.
Cheers.

ok, so you cant use the CDI for both voltages simultaneously ? so CDI for LV and alternate ignition system for HV ?

[Aaron]

lv and hv from same cap

The cap in the cdi is the source of input to the primary of the coil
for the HV, but with the diode setup, it is also the LV source at the
same time.

[dingo]

The cap in the cdi is the source of input to the primary of the coil
for the HV, but with the diode setup, it is also the LV source at the
same time.

I could not get it to work this way....at least on my CDI. LV and HV, individually, are there, but simultaneously, it produces 'nada' or at best, a very faint and weak spark.

[Aaron]

@Dingo

Dingo, can you post a diagram or schematic of your setup?