[Diy_efi] The Hunt effect

Tue Oct 4 22:24:05 UTC 2005

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!

Doesn't about four ounces of acetone in 10 gallons of cheap gasoline make it
burn like a higher octane fuel?  Doesn't ethyl alcohol itself have a
comparativly high octane rating? How about benzene as a fuel additive,
ignoring its health effects?

Thank you,

Dale Mahan

> 
> From: "John Gross" <jogross3 at hotmail.com>
> Date: 2005/10/04 Tue PM 04:11:05 EDT
> To: <diy_efi at diy-efi.org>
> Subject: RE: [Diy_efi] The Hunt effect
> 
> ;-)  Nope, but I did stay at a Holiday Inn Express last night  ;-)  All
> kidding aside, I have a master's in Internal Combustion Engine Design.
> 
>  
> 
> -----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 3:35 PM
> To: diy_efi at diy-efi.org
> Subject: RE: [Diy_efi] The Hunt effect
> 
>  
> 
> WOW John are you a gas engineer???? great explinations of the reactions
> inside an engine
> 
>  
> 
> jim
> 
>  
> 
>  
> 
> 
> 
> John Gross <jogross3 at hotmail.com> wrote: 
> 
> It takes more energy to cause the fuel to "flash" without a specific
> ignition point.  The spark from the plug on your car is more than enough
to
> start the burn on just about any unleaded fuel.  I say unleaded to try to
> keep the discussion within reason in terms of octane ratings and
appropriate
> CRs for the engines.  It takes more spark energy to light off a 115 octane
> fuel than it does an 87.  However, when talking about street-driven cars,
> any delay in the formation of the kernel (the initial point of combustion
> inside the spark plug gap) is so minute, that it is not worth considering.
> Additionally, what makes it harder and harder to light the air-fuel
mixture
> isn't just the fuel, but the dynamic compression.  That's why blower
motors
> typically need a more robust and powerful ignition system..the turbulence
> inside the cylinder in a blown motor (high dynamic compression) can
actually
> extinguish the kernel, thus stopping combustion.  
> 
>  
> 
> One thing to keep in mind, though, is that the kernel starts the
combustion
> at the plug, but once started, there are multiple turbulent pockets of
> burning gas traveling around the combustion chamber, like a bunch of tiny
> eddy currents.  Quite frequently, especially in engines where the octane
> rating of the fuel used is borderline to the dynamic compression of the
> engine, some of these eddy currents will surround a pocket of unburnt fuel
> and air (end gas), and cause the local temperature and pressure to rise to
a
> point where the pocket will explode, instead of burn, causing pinging.
> Usually, this is not enough to set off the knock sensor, but when it
> explodes like that, the release of pressure is instantaneous, and
therefore
> does not contribute to the overall cylinder pressure..therefore you've
lost
> some of the potential pressure.  So, from the uniformity of combustion
> standpoint, running a little extra octane for WOT, max power may help
some.
> But also keep in mind that the fluid dynamics inside an engine are chaotic
> in the truest sense of the word.  A decent engine will have a
cycle-to-cycle
> power production variance of 5% for every given cylinder, meaning that
> cylinder 1 on a 400hp V8 may make 50 hp on this cycle, but only 47.5 hp on
> the next combustion event, or it may make 52.5 hp on the next event.  It's
> all very chaotic.  A lot of the R&D that goes into high end racing engines
> is in the area of reducing cycle-to-cycle variance and the overall
> cylinder-to-cylinder balance, NOT maximizing the output of any given
> cylinder.
> 
>  
> 
> -----Original Message-----
> From: diy_efi-bounces at diy-efi.org [mailto:diy_efi-bounces at diy-efi.org] On
> Behalf Of Bret Levandowski
> Sent: Tuesday, October 04, 2005 11:24 AM
> To: diy_efi at diy-efi.org
> Subject: RE: [Diy_efi] The Hunt effect
> 
>  
> 
> But if higher octane fuel takes more energy to light off, then the
ignition
> point would happen later than it should causing a power loss. Yes??? No???
> I'm thinking out loud. Or would the ECM take these factors into account
and
> advance the timing to compensate? This being the case, older
non-controlled
> motors would show a loss unless the timing were manually adjusted. As slow
> as the older ECM's were (80's), would they be able to adjust fast enough
to
> compensate? (By slow, I mean compared to todays comm speeds.)  Ski
> 
> John Gross <jogross3 at hotmail.com> wrote: 
> 
>   _____  
> 
> Yahoo! for Good
> Click here to donate <http://store.yahoo.com/redcross-donate3/>  to the
> Hurricane Katrina relief effort. 
> 
> 
> 