SNIP<

Now here is the downside to a simple, single spark CD system.
The spark don't last very long :-)>  This is why you need a multiple
spark CD system if you are going CD and you are concerned with low
RPM operation.

If it fires twice or three times that will be twice or three
times the power consumed probably. The power consumed would
probably be about the same as an inductive system.

The story at 6000 RPM and above might be different.
An "ms" or short for milli second is 1/1000 of a second.
At 6000 RPM a two rotor fires twice per rev so that is 100 revs per

second

or 100 sparks per second for each rotor. That allows a total of 100

milli

seconds for each spark. If we relate that to e-shaft degrees that is
.277 milli seconds per degree. A 20 degrees e-shaft angle change takes

5.5 milli

seconds. That is about how long a simple single spark  CD system spark

last anyway.

So it appears there is little advantage at high RPM for Multiple Spark

Discharge

CDsystems. Check my math. I could be wrong.

Paul Lamar

Now here is where it gets interesting.
The top chart shows what is required to fire the plug as a function
of mixture. Note that at real lean mixtures or high MPG the voltage

required

to fire the plug goes up. This is what Klause Saviour LSE  has been saying

for

the past five years or so. There appears to be potential here I suspect.
I am very unsure about this because I don't know at what mixture Tracy's

engine is

starting to misfire when he leans it out.

Tracy?

The other line on this chart is an indication of the electrical insulating

properties

of air. The higher the pressure the better the insulation. The higher the

pressure

the harder it is to fire the plug. Think about that for you turbo guys.
It is also the reason you have to pressurize your magnetos when you turbo
your engine and fly at high altitudes. For those still using mags :-)>

Ignore the lower chart for now.

Paul Lamar

Sliped a decimal point somewhere.  There is only 10 ms / rev at 6000.  I
think the charts you referenced are wrong (or they may have meant
microseconds (us).

Have to go with the simple approach here.  I have seen no evidence of a
voltage shortage on NA or turbo rotaries so I can't get too excited about CD
ignition.  In addition, the long duration of inductive ignition is a benefit
on rotaries since the fuel-air mixture rapidly rotating by the spark plug.
'Corse I'm biased, I still have the scars from a failed CD ignition system
:-)

Tracy Crook
tcrook@rotaryaviation.com
www.rotaryaviation.com

Could be. Would not be the first time that book was wrong.
I'll research it some more.

Paul Lamar
 
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