On 3/9/2012 10:22 PM, DLOMHEIM@aol.com wrote:

Tracy wrote:  >As usual, the in-flight symptom was a rise in EGT on the affected rotor.

 

Can someone describe the science behind a "rise in EGT" when we lose a single coil.  I would have expected a drop in EGT due to less thorough burning of the mixture and therefore excess un-burnt fuel which I thought would provide cooler temps of the exhaust stream as it passes the EGT probe.

 

Must be missing something very basic here...

 

Thanks for any clarity!  :)

 

Doug Lomheim

RV-9A / 13B FWF

The rotor combustion space is long and narrow at TDC. If you ignite the fuel air charge in a rotary at tdc from only one end, the flame front progresses slowly from one end of the "combustion chamber" to the other. Two plugs (and coils) for each rotor are present in order to facilitate complete burning of the fuel-air charge from opposite ends, and to extract as much power from the charge as possible before the "power stroke" portion of rotor rotation uncovers an exhaust port and begins the "exhaust stroke"

So.. in an abnormal condition characterized by a single coil failure (out of 4 coils).. the affected plug is dead... and the affected rotor has incomplete and SLOWER burning of the charge than normal. This delayed burning persists after the exhaust port is uncovered. So instead of exhaust gases (which have already lost heat to the block) passing by the EGT probe, you have actual flame front (from the still burning fuel air charge) passing the probe and combustion continues in the tailpipe. That explains why EGT on the affected rotor would rise in a rotary with dual plugs/coils per rotor. A single dead plug from fouling or other causes could also provide the same result.

Make Sense?
Dave (a lingering former rotorhead)