[Diy_efi] WI, methanol, and corrosion

[Mike]

no, not quite, its not an increase in pressure you are looking for...

Its the fact that water is such a good absorber of heat, in fact
weight for weight its about a million timer better than air !

When water droplets in the chamber are heated enough they absorb
a tremendous amount of heat as they make a 'phase' change into
vapour. ie. From liquid water to vapour (gaseous water) the
heat absorbed is called the 'latent heat of vapourisation' and
is the most helpful part of high water injection rates.
Although some benefit is had from gaseous vapour, the greater
benefit is gained from the phase change in the chamber.

So you dont want droplets too small otherwise they change to
vapour before they get to the chamber and you dont want droplets
too large or they do nutty things ;-)

In fact, the more I think about it, and in concert with what I
have seen over the years - many people may have confused water
vapour with droplets. The former being a gas, the latter being
a suspension in air - the two are radically different in heat
content.

Eg. Which has more heat, liquid water at 100deg C or vapour
at 100deg C - although the temperature is identical, the vapour
has far more heat and can cause far more burns than liquid
water...

rgds

mike



At 10:37 AM 22/1/2003 -0800, you wrote:
>--- bill.shurvinton at nokia.com wrote:
>
>> 2. Why has it been deemed necessary to have
>> vapourised all the water in the inlet
>
>It was my understanding that much of the benefit of
>water injection comes from vaporization inside the
>combustion chamber increasing pressure inside the
>combustion chamber, while also slowing combustion
>slightly to help prevent detonation.  This results in
>a generally greater efficiency under some conditions.
>
>Am I missing something?
>
>=====
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>|   The catastrophe in this case, of course, was that the sun   |
>|     had come up again."                    -Kurt Vonnegut     |
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