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This calculator is equally applicable to all motors,
naturally aspirated (NA), turbocharged and supercharged.
For an NA motor, just set the boost to zero and set the
IC parameters to zero. Supercharged motors will have
a higher SFC than turbo motors due to parasitic losses
in driving the compressor, but are otherwise the same.
Any boosted or non-boosted motor can have an intercooler
or water injection, try it.
You need to make educated guesses on three significant
numbers for this calculator:
- Volumetric Efficiency (VE)
- Air Fuel Ratio (AFR)
- Specific Fuel Consumption (SFC)
If you have grossly bad values for any of these three
quantities, then the estimated results will be correspondingly
bad.
Other values such as turbo and IC efficiency are not
nearly so sensitive (try a test with 50% and 100%, then
look at the difference in HP values.
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The water injection system modeled here allows you to
select the location for the injector: before the compressor
inlet, between the compressor and the IC, and after the IC.
(With a little bit of thought you will see why when you
have no intercooler, the injector should be first; when
you do have an intercooler the injector should be last;
in no cases does it make sense to inject between the turbo
and the intercooler, try it. Here's a hint: if you inject
before the intercooler and cool the charge below ambient,
the intercooler will heat the charge back up).
The model assumes dry air (0% relative humidity) and
complete vaporization of the injected water/methanol stream,
and hence grossly incorrect results will be produced if
you attempt to inject large quantities of liquid (or if
you even inject small quantities on a very humid day).
If you see the post-injection temperature ("Temp out WI")
dropping well below the ambient temperature, then you are
pretty surely in the realm of incomplete vaporization and
the results are wrong.
Note that only the thermodynamic effects
of the injected liquid on charge temperature are
considered here; all combustion-related effects are
ignored (it is assumed that you will tune the SFC
value correctly to compensate).
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Use the value in the "Pressure Ratio" output field
as the Y-axis (vertical) coordinate on a pressure map.
Pressure ratio is measured at the turbo outlet, and is
the sum of the ambient pressure, manifold boost and the
pressure drop across the intercooler. Most texts compute
this value without regard for this last term, which for
some installations can be quite large.
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Most pressure maps use the LBM flow value on the X-axis
(horizontal) coordinate, but some use the CFM flow value.
LBM is much more accurate because it takes into account
density ratio, whereas CFM varies grossly with temperature.
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Hey, these torque and HP numbers are ESTIMATES based
on your own faulty data! Do not quote these values to your
local law enforcement officer or on some internet newsgroup,
they are not real numbers. Remember that you are merely
guessing at the VE, SFC, AFR and cetera, so unless you
really know what you are doing, they are probably off by
±20% or more.
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Injector size is computed directly from the SFC, AFR and
maximum injector duty cycle values that you enter. If you
have accurately estimated these values, then the injector
size should be very close to correct. Note that injector
size is estimated for the displayed configuration, so you
should record the setting only when you have a maximum
HP estimate shown. Note also that this is the actual
injector size you should use. Some tables show injector
sizes in terms of 100% duty cycle, beware that you will
need larger injectors than these tables show!
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When you click the "Save" button, all of the parameters
that are shown in fields are placed in the location bar of
your browser. You can then copy the link into an e-mail,
or save it and come back to that same configuration later.
You can often shorten the link line up by deleting parameters
that are not useful, or have default values.
