DIY_EFI Digest V5 #251

[Robert Harris]

First - digest members - for some reason I did not receive #250 - so if
someone would forward a copy I'd appreciate it.  

Next, water does not speed combustion up - all I said was that it was very
active in combustion and that the introduction of water changes combustion.

Then - most of the research was done on aircraft engines operating at 1800 -
3500 rpm with centrifugal superchargers.  The largest improvement was at near
full load under boost.

When you are approaching detonation is one time to consider water injection.
When you apply the normal methods - less than optimum spark - rich fuel
mixture - etc of moving away from detonation are about the right point to
consider using it.  Another good point is when you have to start making the
mixture rich to make more power.

Engine speed enters into the equation because of temperature.  Typically as
the RPM increases, the effective compression increases and the temperature at
the end of the compression stroke increases.  With the larger thermal energy
present "temperature", water injection as an alternative to more fuel begins
to be attractive.

The substitution on non-fuel - whether EGR, or water - for fuel is feasible
because of the low ( about 32% typical ) conversion of the energy in fuel to
mechanical power.  Adding excess fuel increases the heat much faster than it
increases the pressure and some of this can be replaced with an non-fuel that
increases the molar product - increasing the pressure from the available heat.

On Mon, 10 Jul 2000 20:03:38 -0700, you wrote:

>Also, it seems that the benefits of water on combustion are realized at high
>rpm "It is important to note that these improvements came at the upper end
>of the power range where sufficient fuel and air was available to have an
>excess of energy that could not be converted to usable pressure in a timely
>manner." said Mr. Harris.
>
>So I'm interested in knowing the approximate speed referred to as "the upper
>end of the power range". If we are talking F1 engines, it may well be around
>18000 rpm or more.

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