Date:         Tue, 12 Jun 2007 12:16:50 -0400
Reply-To:     Jim Akiba <syncrolist@BOSTIG.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Jim Akiba <syncrolist@BOSTIG.COM>
Subject:      Re: E85 thermodynamic advantage?
In-Reply-To:  <HHEAJIOMDPBGGCKHACGJAEDNCMAA.al_knoll@pacbell.net>
Content-Type: text/plain; charset="us-ascii"

Good question... and you needn't have quoted Kelvin or Feynmann, you're
preaching to the choir. But they are great quotes.  You're right, it is of
little value to examine the fuel alone, but it needs to be done within the
context and system in which it is used, in a reciprocating combustion
engine. I'm excited because I went straight to the paper in my ethanol
research folder on our network storage(sweet, everyone should have one).
The specific power of the engine with ethanol is higher than with gasoline
mostly because of the slower burn characteristic of the fuel, and the extra
oxygen atom to aid combustion. Ethanol can run higher compression ratios and
combustion pressures which equal higher volumetric and thermodynamic
efficiencies via a better burn even at the same compression ratios(which
needn't be the case). You can affect combustion pressures(and dynamic comp
ratio) to good effect via spark and fuel table adjustments in firmware,
unless you can't. Check out this paper(it's rights managed, so you have to
pay like me, but if you aren't an sae member it's slightly more):

SAE Technical Papers
Title: Exergetic Analysis of Ethanol and Gasoline Fueled Engines
Document Number: 920809
http://www.sae.org/technical/papers/920809

Or here's a quick excerpt from the conclusion:

"The exergetic analysis shows that the combustion efficiency for the ethanol
fueled engine is higher than for the gasoline version, when compared in the
same range of relative air fuel ratio. For the ethanol engine, even when the
compression rate is the same as for the gasoline version, the results showed
that exergetic efficiencies are higher. This indicates that the ethanol
exhibits a less irreversible combustion than gasoline"

And for your numbers:

http://www.bostig.com/files/ethanolexergeticeff.gif


Jim Akiba







-----Original Message-----
From: Pensioner [mailto:al_knoll@PACBELL.NET]
Sent: Tuesday, June 12, 2007 10:48 AM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: E85 thermodynamic advantage?

Jim sez>
 but ethanol is still the better
fuel from an engine/thermodynamic standpoint.

Do tell.  I am interested in how it is a better fuel from a thermodynamic
standpoint.  BTU/unit volume (not likely) or some other measure?

Lord Kelvin is reputed to have said that  "if one professes knowledge but
cannot express that knowledge in numbers, then his knowledge is of a meagre
and insufficient kind"

Feynmann was noted for statements like..."No matter how elegant the
hypothesis, or how eloquent it's presentation, if it doesn't agree with the
data, it's wrong"

Walt Kelly penned "We have met the enemy, and he is us"  Not the van, not
the E85, US.

Just point me to the literature reference where the thermodynamic advantage
is explained and we can go from there.