From: rick@posms.cactus.org (Rick Kirchhof)
Subject: Re: Spark plug wires and radio interference
Organization: Department of Redundancy Dept., Austin
Date: Mon, 27 Jul 1992 05:36:03 GMT

In article <711939646.F00002@blkcat.UUCP> Frank.Mallory@f417.n109.z1.fidonet.org (Frank Mallory) writes:
> RK> One of the main reasons that resistance wires are used, is they are 
> RK> very
> RK> helpful in creating a more consistant spark.  It is true that the
> RK> radio interference is greatly redused by using resistance in the
> RK> secondary ignition (spark plug) wires, but as early as 1960 even
> RK> Volkswagen used solid core copper wires with a screw on resistor at the
> RK> spark plug connection.  This was done to up the required voltage for 
> RK> arc
> RK> over.  This tends to make the spark more reliable by delaying the
> RK> start of the spark until higher voltages are present.  Less misfires 
> RK> are
> RK> the result.
>
>Sorry to have to disagree with you; but my understanding is that the function of
>resistance in the HT wires or connectors is to reduce the _current_, not the
>_voltage_.
>
>The Bosch Technical Instruction on Battery Ignition Systems lists the following
>factors determining the requirement for firing voltage in Kettering ignition
>systems:
>
>1) Spark plug gap
>2) Condition of electrodes
>3) Shape of electodes
>4) Electrode material
>5) Polarity of center electrode
>6) Temperature at the electrodes and in the combustion chamber
>7) Composition of mixture
>8) Compression of mixture.
>
>Series resistance is not a factor provided it is low in relation to the spark
>plug gap and other resistive factors.
>
>The Bosch Technical Instruction goes on to say, "All electrical systems must be
>provided with all necessary interference suppression devices so that outside the
>vehicle interference-free radio reception is guaranteed. Since 1958 all German
>automobile manufacturers have equipped the vehicles they produce with long-range
>interference suppression equipment." " The most effective devices for
>suppressing interference are ohmic resistors, capacitors, inductors (chokes),
>and grounded cable shielding."
>
>
>
> RK> 
> RK> Spark ignition in a Otto cycle engine is high probability rather than a
> RK> certainty even when all components are in excellent condition.
> RK> -- 
> RK> Rick Kirchhof   Austin, Texas                   | Experience is what 
> RK> you
> RK> Domain: rick@posms.cactus.org                   | get when you don't
> RK> Bang path: ...!cs.utexas.edu!peyote!posms!rick  | get what you want.    
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>
>
>

I would point out that you are dealing in design theory.  That is great,
but you must at some point introduce reality.  I will explain:  Remember
the "super ignition activator" or some such usually sold as a ignition
cure all.  These devices are usually an auxillary spark gap.  If there is
enough power to jump the auxillary gap, it will fire the spark plug as
well.  Champion and other manufacturers make a spark plug with an
internal booster gap.  These plugs are superb if you MUST continue to run
an engine that burns a lot of oil.

Extend this concept to a used spark plug.  All spark plugs constantly
fight the battle between overheating themselves and fouling out.  In any
engine, there will be times where the conductive buildup on the center
electrode insulator is close enough to the electrode itself that no spark
will occur.  Current delivered simply leaks away on the conductive
coating.  Most drivers have experienced a time where they could use
1/2 or slightly more throttle and get good power, but would feel shaking
and loss of power when the throttle was pressed further.  Once required
voltage needed for ignition exceeds available voltage, by definition,
misfire is the result.  Likewise, if the voltage is leaked or drained
away by conductive or sometimes conductive deposits, the spark will not
occur.  What happens in the above example is that the engine
compression pressures rise, require more voltage, and overcome the
available insulation on the spark plug ceramic.  Current offered takes
the path of least resistance, and no spark is the result.

The principles used in various ignition add ons and alternate designs try
to eliminate or reduce misfire caused by the engine reality of conductive
buildup.  Increasing secondary resistance, will to a measureable degree,
overcome some of the misfires and spark voltage drain away that would
otherwise occur with less resistance because the voltage rise is more
sudden at the plug.  Similar steps are used inside the distributor with
wider rotor to distributor cap air gaps.  Capacitive discharge is an
extension of this theory in that the voltage rise is exceedingly fast.

I stand by my statement.

-- 
Rick Kirchhof   Austin, Texas                   | Experience is what you
Domain: rick@posms.cactus.org                   | get when you don't
Bang path: ...!cs.utexas.edu!peyote!posms!rick  | get what you want.            
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