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From: Bulent Aliev <atlasyts@bellsouth.net>
Subject: Re: [FlyRotary] Re: Spark plug gap (was Re: Another case of heat-soaked coils?
Date: Thu, 25 May 2006 22:16:18 -0400
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>


On May 25, 2006, at 9:22 PM, Lehanover@aol.com wrote:

> In a message dated 5/25/2006 10:28:27 A.M. Eastern Daylight Time,  
> atlasyts@bellsouth.net writes:
> Lynn, where do we stand with John? Our engines have the high
> compression rotors and they are turbo charged. Should we use different
> plugs than the stock ones that everyone uses?
> Thanks
> Buly
> http://tinyurl.com/dcy36
> The correct technical answer is that I have no clue. The very  
> coldest plug possible would be my best guess. The "stock turbo"  
> plugs should do well. The turbo engines run lower static  
> compression because the turbo and supercharged engine keep changing  
> displacement as the boost goes up and down. The head space is  
> always the same, so the dynamic compression ratio can go way up  
> very fast in operation.
>
> So, if the boost is way up, and you are force feeding 160 cubic  
> inches of mixture to your 60 cubic inch engine, have you raised the  
> compression ratio?
>
> Controllers designed for turbo use have a retard feature the is  
> actuated by the Lambda knock sensor. At the first hint of knock
> (detonation) the lambda pulses the controller and the controller  
> pulls out, say, 2 degrees of advance and waits for another  
> revolution to be completed. If it gets another Lambda hit it will  
> pull out another 2 degrees, and so on.
>
> This saves the engine by reducing combustion chamber heat.  
> (Detonation is charge temperature dependant). It also reduces  
> engine power over the short run. Other inputs can reduce charge  
> heat, for example a temp sensor might light a warning light, as  
> well as the Lambda hit through the controller. A temp sensor might  
> also switch on a water spray to the water and or oil coolers. Or  
> the inter-cooler.
>
> The object of ignition timing is to develop the highest cylinder  
> pressure at the correct crankshaft angle for maximum efficiency.  
> Note that retarding the timing is therefore reducing efficiency.  
> This would involve many items such as burn rate, compression ratio,  
> chamber temp and soon.
>
> Note also that higher cylinder pressures increase ignition voltage  
> requirements. So turbo, and supercharged engines have very exotic  
> ignition systems. Lower boost numbers less trouble.
> Higher boost numbers more trouble.
>
>
> Lynn E. Hanover

Thanks Lynn.
Buly