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Date: Tue, 16 Feb 2010 13:16:25 -0500
From: Ernest Christley <echristley@nc.rr.com>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Runner velocity; injector placement
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Al Gietzen wrote:
>
> As I see it; injection at the ports is good for cold starting. 
> Injectors some distance away from the ports gives better vaporization. 
> Injectors too far away from the ports; like maybe more than a foot or 
> so, results in liquid fuel on the runner walls, especially when cold 
> or at lower rpm. I think Mistral found this out when they initially 
> had the injectors quite a distance from the ports.
>
Megasquirt calls this phenomena Tau, and they have a setting to control 
it.  When you cut the throttle, the engine will pull in some of the 
"sidewall fuel" and run rich for a moment.  If you goose the throttle, 
some of the extra fuel will be depositing on the runners instead of 
powering the engine, making it run lean for a moment.  The control 
setting will add or subtract fuel as needed to make for smooth 
transitions.  They can't just use a static setting, because it is 
dependent on a lot of variables like injector size and runner length.