Leaning and more ignition advance go together. Leaner mixtures burn slower, so advance is added to keep maximum cylinder pressure at 50 degrees after TDC. In some installations, lean cut off may be crisp with no misfires at all. More like an ignition switch turned off.

 

The RX-8 had closed throttle maps up to 44 degrees.

 

Adding a high energy ignition system with large plug gaps may get you further into lean burn. This would be where I would experiment with high energy on the trailing ignition and split timing events. After maximizing lean performance, I would go to higher coolant and oil temps and record those data.

 

Lynn E. Hanover

 

Gordon and Ernest,

The BSFC units are Lb/Hp-Hr as you expect.  Around 0.6 is as low as is usually seen with my setup under normal operating conditions.  I've seen as low as 0.52 with very aggressive ignition timing advance settings, but these settings probably would not be used over the long term.

Generally, the engine does not run rough as it looses power when the mixture is leaned.  Eventually, the point is reached where it just dies.

Steve

________________________________________
From: Rotary motors in aircraft [flyrotary@lancaironline.net] on behalf of Ernest Christley [echristley@att.net]
Sent: Thursday, May 17, 2012 7:09 AM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: BSFC and EGT

Gordon Alling wrote:
> If I read this plot correctly, the SFC is reported between 0.6 and 0.7 over
> most of the range.  What units are used?  Lb/Hp-Hr?  If so, this seems a bit
> high for a four-stroke spark ignition engine at cruise setting.  I would
> expect to see 0.45 - 0.55 Lb/Hp-Hr.
>

That was my thought, too, Gordon.  I also notice that the BSFC is almost static between 0 and -175 or so.  Seems to make
sense.  The efficiency gained by using less fuel in the mixture would be offset by the efficiency lost by the mixture
not being rich enough to burn completely.  That condition would hold for a bit until it gets so lean (and cold) that it
will hardly burn at all.  The bottom end where the BSFC curve shoots up dramatically is probably where the engine is
running rough from a increasing number of misfires, all the way to the point where it won't run anymore?

This again makes me wish I had added the GPIO board to my MegaSquirt, so that I could record EGT.

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