Date: Thu, 5 Aug 2004 12:57:44 -0500
Reply-To: John Rodgers <jh_rodgers@BELLSOUTH.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: John Rodgers <jh_rodgers@BELLSOUTH.NET>
Subject: Re: ECU and Throttle Question
In-Reply-To: <002501c47a62$c3e20610$0100a8c0@korky>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Interesting questions, interesting points.
In my pilot training and mechanic days, we dealt with three power points
on piston engines. With the throttle wide open, or set by chart for
altitude and horsepower, the mixture control could be adjusted to three
settings.
1), Lean Best Power - lean the mixture to peak temperature, then
continued leaning until the exhaust temperature begins to drop. That is
the point of lean best power.Fuel/air ration has lots more air. Burns
ALL the fuel, burns clean. It yields the greatest range for the fuel
burned. Power is low, low chance of engine damage.
2) Rich best power - achieved by leaning to peak exhaust temperature,
then enriching until temperature drops from peak on the rich side. This
setting protects the engine with extra fuel to aid cooling to prevent
detonation at high power settings Not so efficient, as some fuel is not
burned, but the engine cools well, so no damage. On takeoff, maximum
power is developed and requires a very rich mixture to provide added
cooling under the load. At altitude that can be adjusted.
3) Best Power - the mixture is leaned until the exhaust temperature is
at it's peak. - this gives the greatest horsepower and speed, but
burns more fuel and can damage the engine if sustained for any length of
time.
From my experience with the airplanes, I would say that the "pegged in
the rich area" condition is not only for the purpose of producing max
power, but also for adding enrichment fuel for added cooling needed to
prevent detonation under a load.
The newer engines - TDI and others - have really good anti-knock
sensors, and the ECU's can allow the mixtures to run closer to peak lean
conditions at max power without damage, than can our Vanagons ECU. Seems
Bob Donalds addressed this issue one time in the past. Interesting subject.
Regards,
John Rodgers
88 GL Driver
Ken Lewis wrote:
>Here's my theory FWIW; the thinking behind the activation of the full
>throttle switch means you have "floor-boarded it" i.e. you need all she's
>got plus some. Looking at the O2 sensor monitor gadget (
>http://neksiwel.20m.com/photo5.html ) on my dash the FI system has stopped
>toggling the mixture rich-lean-rich-lean and is now pegged in the rich area.
>How much richer I do not know.
>
>Ken
>
>----- Original Message -----
>From: "David Beierl" <dbeierl@ATTGLOBAL.NET>
>To: <vanagon@GERRY.VANAGON.COM>
>Sent: Wednesday, August 04, 2004 4:00 PM
>Subject: Re: [VANAGON] ECU and Throttle Question
>
>
>
>
>
>>Which brings up my own little question: What is it about the last .010 of
>>throttle plate movement that requires enrichment, that the previous .010
>>did not? Under what conditions is the enrichment actually needed and when
>>is it wasted? And roughly speaking how much is added?
>>
>>
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