[Diy_efi] The Hunt effect

Tue Oct 4 20:47:42 UTC 2005

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. 
> 
> 
> 
-------------- next part --------------
_______________________________________________
Diy_efi mailing list
Diy_efi at diy-efi.org
http://lists.diy-efi.org/mailman/listinfo/diy_efi