Fw: Fw: Holden Commodore, Aerodynamics. AND NOW: WATER INJECTION...

[Raymond C Drouillard]

I follow your reasoning, but I don't follow your use of the ideal gas
law.

You are saying (correct me if I am wrong) that the pressure at TDC is
high enough to keep the water in the liquid phase because the boiling
point is so high at that pressure.

As the piston drops and the pressure tries to fall, more water will flash
into steam, keeping the pressure higher than it would be without the
water.  This will increase the power output.  The trick is to inject the
proper amount of water.  You would want to run out of water on the way
down so that the pressure can drop before the exhaust valve opens.

To get an idea if this will work, you'll have to look at a steam table. 
That table lists the boiling point of water at various pressures.  You
can also get the mass density of the steam at various temperatures and
pressures.  You would normally use the ideal gas law (PV=nRT) to
calculate this, but steam isn't an ideal gas until you get well above the
boiling temperature at that pressure.

Even nitrogen and oxygen aren't ideal gases at room temperature and
pressure.  They're really close, though.  We did an experiment in
chemistry class where we did some measurements and compared them to the
ideal gas law.  They were off by a few tenths of a percent.  We then used
Van Der Wal's non-ideal gas formula to calculate the expeted pressure and
volume and found it to match the ideal gas law to within about six or
seven significent figures.  The difference was trivial compared to our
experimental error.

That isn't the case with steam.  The differences are significent.

I'm sure that someone on the list can tell us what the typical and
maximum temperatures and pressures are at TDC.  Also, maybe someone can
point us to a steam table somewhere on the web.

Hmmm... I just thought of something:
If injecting water results in a lower exhaust temperature, more heat will
be used to power the engine and less will be wasted out the exhaust.  If
the water is vaporizing as the piston drops (as explained above), the
exhaust temperature will be lower because the water is absorbing the
heat.


Ray Drouillard, BSEE



On Sat, 2 May 1998 18:16:05 +1000 (EST) danny_tb at postoffice.utas.edu.au
(Danny Barrett) writes:
>G'day there, when I consider the things I've been taught in my physical
>chemistry calsses (before college, and during my Engineering degree that
I
>am currently doing), the water should (I won't say will - I could be
wrong)
>stay in the liquid phase until after TDC. Look at the formula:
>
>PV=nRT
>
>P=pressure in Pascals
>V=volume in m^3
>n=amount of a gaseous mixture in moles
>R=universal gas constant
>T=trmperature in Kelvin.
>
>Also, find a table of the boiling point/Vapor Pressure of water at a
given
>temperature.
>
>Find your TDC pressure.
>
>Find some value of maximum combustion heat (usually above about 900 deg
C,
>as NOx gases are produced).
>
>If you know how to use the formula, you'll find that the water should
remain
>a liquid until well after TDC, even if it started off as a vapor before
>compression. Of course, I could be wrong. But I did some calc's about a
year
>ago, and I found that you need a boiling point of about 40 deg C before
a
>gaseous substance will stay a gas at TDC. Of course, I will repeat again
>that I could be WRONG, so it might still need to be researched.
>
>Danny Barrett.
>
>>Mike:
>>
>>Yes, I agree ...research project
>>
>>Timing water phase change requires work.  We all know that the rate of
>>evaporation of a liquid dropplet suspended in a gas phase is a function
of
>>the following variables:  local turbulence, local temperature
gradients,
>>local pressure surfaces, and dropplet size.  Vaporization is driven by
>>fugacities of the gas phase versus the liquid phase.  Experimentation
would
>>have to be done with both dropplet size and injection temperature.
>>
>>Wayne Strasser
>>Chemical Engineer
>>EFI Patent Pending

_____________________________________________________________________
You don't need to buy Internet access to use free Internet e-mail.
Get completely free e-mail from Juno at http://www.juno.com
Or call Juno at (800) 654-JUNO [654-5866]