Plasma Jet Ignition

[Robert Harris]

Very Politically Incorrect and probably offensive - but its the best way to
describe it in common terms.

I want to blow up a building.  I fill a truck with ammonia nitrate.  I
detonate truck.  Oops - just blew out a bunch of windows  - blast wave and
heat go out in a hemispherical ball.  That's conventional ignition.

So I rent another truck, fill it with ammonia nitrate and add a couple hundred
gallons of nitro methane.  Damn - much bigger blast - but because it still
goes out in a hemispherical ball ( actually probably closer to a donut shaped
ball), all I do is blow out windows at a longer distance.  That's CD ignition.

Next try, I line the bottom, 3 sides and top with thousands of pounds of sand
so that all the explosive force is directed out one side.  Voila - success and
a well deserved death sentence.  That's a plasma jet

Why plasma?  Velocity - the blast wave can hit 10 to the 4th meters per
second, pressure - several hundred atmospheres, temperature - ~60,000k.
Channeling this into the chamber virtually assures the reliable combustion of
the mixture.  Since 94% plus of the energy is converted to plasma during the
plasma stage, you get the most bang for the joule.

Why doesn't just increasing the energy work - see hemispherical ball concept.
Thats also why auxiliary gap plugs, nology wires and add on caps may or may
not show any results  

Assume a perfect intake and perfect injection.  Each cylinder every time
receives identical amounts of fuel and air.   Should be very consistent, yet
there is cyclic variations in power.  Why - the fuel air mixture seen by the
plug varies from very lean to very rich to everywhere in between depending on
too many depending ons.  Swirl, temperature, rpm etc etc all add up to the
plug never see's a consistent mixture - even though the aggregate mixture is
perfect and consistent.  The plug only sees an instantaneous 2mm ball at
firing and that ball determines much of the ignition time for that event.
That's why multi strike ignition works well.  If the first strike is too lean,
maybe the next will be in different air that is combustible.

The Plasma Jet however fires a cone of plasma that may be 5 mm in diameter and
in excess of 10mm deep into the combustible mixture.  It "sees" a lot more of
the mixture and thus far more consistently ignites the mix.

Next, the plasma jet starts a much larger flame front, which greatly shortens
the induction time of combustion.  This translates to less advance needed.
Also the much larger ignition cone easily ignites lean mixtures, high pressure
mixtures (from compression or boost ) and hard to ignite alcohol or nitro type
fuels.

As to multiple gaps vs one, the best I understand is that although the break
over voltage may be similar, the maintaining voltage and current is much
smaller.  And the purpose of the second gap is not spark related as is the
first gap but to simply force the ignition to pump to a higher energy level
prior to firing.  Simply increasing the gap may result in an unstable or weak
initial plasma field.  

As for the pre-chamber, many of the patents are for replacements for spark
plugs so much so that perhaps with a modified anti-fouler to give a small pre
chamber and enough energy at the right time, it should be adaptable to any
engine.  At least that's what I hope.

The gap can be internal or external - but should be as close as possible to
minimize the inductance between them.  The final design implied that both the
cap and the gap were internal to the plug to minimize EMI.

>From: steve ravet <Steve.Ravet at arm.com>
>Date: Thu, 25 Feb 1999 10:06:02 -0600
>Subject: Re: Plasma Jet Ignition
>
>Robert Harris wrote:
>> 
>> Two Parts to the Plasma Jet Ignition.
>
>I'm fascinated by this plasma jet ignition idea.  But, I'm not sure what
>the difference is between what is described below and a typical CD
>ignition, except perhaps the energies involved, and the pre-chamber.  Is
>that pretty much "it"?
>
>- --steve
>


>Why two gaps, and not just one big gap?  Is the auxiliary gap in the
>chamber also, or in a plug wire or something?
>
>
>- -- 
>Steve Ravet
>steve.ravet at arm.com
>Advanced Risc Machines, Inc.
>www.arm.com
>


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