[Diy_efi] The Hunt effect

[Geddes, Brian J]

Where does one go to pursue such a degree?

________________________________

From: diy_efi-bounces at diy-efi.org [mailto:diy_efi-bounces at diy-efi.org]
On Behalf Of John Gross
Sent: Tuesday, October 04, 2005 1:11 PM
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: 

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