[Diy_efi] Re: sequential injection timing

[Garfield Willis]

On Wed, 31 Jul 2002 09:15:14 -0400, bearbvd at mindspring.com (Greg
Hermann) wrote:

>At 10:50 PM 7/30/02, Steve Neese wrote:
>>Guess what else it does!!  From Heywood:
>>
>>"Experimental data show that the decrease in air temperature that
>>accompanies liquid fuel evaporation more than offsets the reduction in
>>air partial pressure due to the increased amount of fuel vapor: for the
>>same heating rate, VE with fuel vaporization is higher by a few
>>percent." p.211

>First, he's only talking about adiabatic fuel evaporation to the point =
of
>reaching the saturation pressure with respect to fuel vapor in the inlet
>tract--NOT about adding enough heat to evaporate all of the fuel !

Nobody in the thread was talking about anything else. His (Steve's) post
is perfectly to point-counterpoint. Your post suggested ANY vaporization
of petrol was a lose-lose situation, pitting atomization and
vaporization against each other. That's why the guy astutely posted the
above rejoinder. Heywood's comment, if you'd read the quote this fellow
has above, and it's further context, in his discussion shows what he has
in view is atomization ALONG with vaporization up to the saturation
vapor pressure, does indeed provide a NET gain, albeit slight.
Obviously, the remainder of the fuel mass will burn all the
better/faster, the more finely atomized it can be made, just short of a
phase change.

The point is, your assertion that any vaporization robs you of precious
oxygen and 'therefore' results in a net loss of power, is FALSE, and
this fellow is just pointing that out to you. That it IS false should be
obvious to anyone familiar with the standard modern EFI practice of
squirting a portion of the fuel on the backside of the hot intake valve.
That's going to increase *vaporization*, not atomization. And that
atomized petrol hitting the backside of that hot valve is very much
still a part of the intake tract. If vaporization up to the saturation
pressure were a 'bad thing' for petrol as you've tried to paint it, you
wouldn't see that practice; rather, they'd be avoiding it.

The KEY reason for the "experimental data shows" clause in the Heywood
quote, is also exactly the reason why Heywood's knowledge of the
experimentation in this field, and his citation of it, is so valuable.
When you model SI engines, you make certain assumptions about the
thermodynamics of processes, to keep things simple. BUT you always have
to check with experiments to see just how well these assumptions sit
with the real whirled. The passage above quoted in right in the section
where assumptions about how much heating effect occurs to the intake
charge is being checked. He grants that the adiabatic model doesn't hold
exactly, and that there IS some heating, and then goes on to say how the
experiments VALIDATE the current practice of modeling the VE dependence
on charge temperature ratio as a square-root dependence. In fact, his
reference in the paragraph following the one Steve has posted, points to
the standard practice of dyno correction factors being based on a
square-root relationship of VE dependence on inlet temperature ratio of
actual to standard conditions.

=46inally, the footnote to Heywood's assertion above, that petrol fuel
vaporization does NOT lead to a significant drop in VE, but rather in
fact a slight gain, but really is about a wash ("a few percent
improvement"), refers to a Japanese study titled, "The Evaporation of
=46uel and Its Effect on Volumetric Efficiency." It's precisely because
this issue is SO important for other kinds of fuel. Indeed, just prior
to the quote that Steve gave, here is Heywood's introduction to the
section where he proves the contrary of YOUR assertion, Greg.

"For conventional liquid fuels such as gasoline, the effect of fuel
vapor [on volumetric efficiency] is small. For gaseous fuels and for
methanol vapor, the volumetric efficiency is significantly reduced by
the fuel vapor in the intake mixture." He then goes on to cite the
results that prove this assertion, as I mentioned above.

I might suggest your distaste for scientists like Heywood who feel bound
to the age-old practice of checking high-falutin theories against actual
practice, is because you're more attune to shooting the breeze than
checking the actual weather conditions, ifyouseewadamean.

Good point, and post, Steve. Don't mistake a mere breeze for a actual
climate report. :)

Gar Willis
Principal Engineer
EGOR Techno
3491 Edison Way
Menlo Park,  CA  94025
650-216-9874
garwillis at msn.com (email and PayPal transfers)
www.egortech.com (website best viewed with IE)



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