[Diy_efi] The Hunt effect

[John Gross]

It takes less air to burn an equivalent amount of fuel, but since an engine
is an air pump, it?s typically better to look at it from the other
direction
.you need more fuel to run the engine at stoich at a given load
and given rpm with alcohol.  Methanol has about half the AFR of gasoline
(6.5 stoich compared to 14.7), but half the energy.  Where methanol is able
to make its power over gasoline is 2-fold.  First, it has an equivalent
octane rating of ~113, so you can run a lot of compression, boost, whatever.
Secondly, it absorbs much more heat (almost 4x) than gasoline when it
evaporates, meaning that it greatly reduces intake air charge temps, making
the charge more dense, allowing more mass of air and fuel to be inducted.
If you look at the intake manifold of an alcohol dragster on a 100 deg F day
after it makes a ? mile pass, there?s ice on it.  Long story short, alcohol
engines run cooler, are less prone to knock on an equivalent engine compared
to gasoline, need more fuel to make the same power, BUT, could possibly make
more power on the same engine if correctly configured.

 

-----Original Message-----
From: diy_efi-bounces at diy-efi.org [mailto:diy_efi-bounces at diy-efi.org] On
Behalf Of Jim Butterfield
Sent: Tuesday, October 04, 2005 7:32 PM
To: diy_efi at diy-efi.org
Subject: RE: RE: [Diy_efi] The Hunt effect

 

Hey John ,can I ask the master a question... as you said below the alcohol
AFR is 9:1 so 1)does this mean it takes less air to burn... and 2) given
two engines equal, on setup with proper alcohol required fuel delivery, will
the ahcohol car get more HP if the pcm/ electronics were tuned for the
alcohol????? if so any guess how much HP imporvment???? How does the alcohol
act under a bloan application... heat, detnoation-knock etc....

 

thx

jim

John Gross <jogross3 at hotmail.com> wrote:

I'd have to look at the ratios, but yes, certain additives like ethyl
alcohol have an effect on octane ratings. HOWEVER, keep in mind that ANY
alcohol will dry out any rubber seals, o-rings, etc in a fuel system
designed for straight gasoline. Also keep in mind that ethyl alcohol burns
at a stoich AFR of 9:1 (it's an oxygenated fuel), so if you blend it into
gasoline, it will change the required pulse width of your injectors to
maintain the correct lambda. Also, it will tear up your injectors because
they're not designed for alcohol either. That's why you can't just run E85
in an everyday car. The fuel pump, fuel lines, injectors, o-rings, seals,
and even fuel tank liner must be designed to work with alcohol-based fuels.

-----Original Message-----
From: diy_efi-bounces at diy-efi.org [mailto:diy_efi-bounces at diy-efi.org] On
Behalf Of dalemahan at charter.net
Sent: Tuesday, October 04, 2005 4:48 PM
To: diy_efi at diy-efi.org
Subject: Re: RE: [Diy_efi] The Hunt effect

Hi John,

Ah hah - a chance to ask a real IC engineer about fuel questions!

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