Date:         Fri, 23 May 2008 15:49:50 -0400
Reply-To:     Allan Streib <streib@CS.INDIANA.EDU>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Allan Streib <streib@CS.INDIANA.EDU>
Subject:      Re: Increasing fuel economy/decreasing con$umption
Comments: To: pickle vanagon <greenvanagon@GMAIL.COM>
In-Reply-To:  <91c8f9760805230947s20ec6c78g1af2cbb0422741f0@mail.gmail.com>
Content-Type: text/plain; charset="ISO-8859-1"

"pickle vanagon" <greenvanagon@GMAIL.COM> said:

> This seems a little crazy.  The engine is burning about as much fuel
> idling as when driving 30mph?  That can't be right, can it?
> Maybe what they meant was that the emissions were as bad?  That seems
> more likely.

Gasoline engines require a pretty specific fuel/air mix to burn properly
when the spark plug fires.  At idle, you still need to provide enough
fuel to attain that proper mixture, even though the power needed just to
keep the engine turning is much less.

Diesel engines idle very efficiently, because they ignite by compression
not spark, and at idle you only need to burn enough fuel to keep the
engine turning.

It is not particularly GOOD for a diesel engine to idle for a long time,
because they generate very little heat at idle and they can get sooted
up.  BUT, they do use very little fuel at idle and so are better in stop
and go traffic in that sense.

Allan
--
1983 300D