Turbo Chubby parts

[Bernd Felsche]

Bob Wooten tapped away at the keyboard with:

> You are SOO good @ keeping us on the edge of our seats.

Based on what's been written before, he's using compressed air to
feed and shear the water for best atomisation. As long as the air
flow rate is known/measured, there's not a real problem introducing
the extra air.

The use of air avoids direct contact with valves, pumps, etc.
The only WI components exposed to air AND water are then the
injector jets. The jets don't need moving parts. A check valve
in the water feed line will prevent the turbo blowing back though
that line. A sequence of compressed-air valves can be used to
persuade that same valve to close on demand, cutting water flow
in the forward direction.

> High pressure = easy to maintain nice spray patterns in all conditions,
> something about "overwhelming the manifold conditions" thing.

> fogger nozzles for easy availability.  I suppose this application
> could really use someone to come up with a single injector nozzle
> similar to a fogger nozzle that would be simple to change jets on,
> or better yet, have a single nozzle/jet for all locations & have a
> variable jet somewhere else (or pressure, but then we get into
> critical flow or not).

According to the people who make some money from it, 
(e.g. http://www.aquamist.co.uk) there are several locations where
you can introduce water injection for a variety of benefits. There's
no "perfect" location. Upstream of the intercooler is best for
vapourization, adding to the effectiveness of the intercooler
(charge density) and distribution from a single jet.

The closer you inject to the inlet valves, the greater the
proportion of droplets and from a single injector, the greater the
chance of imbalance. A port water-injector minimises vapourization
but droplet sizes need to be very small. Distributing the right
amount of water to each requires careful tuning and/or management.

> what do I want?  I think that I want vaporization for increased
> economy & atomization for power.  Warm, tepid or cold?

The _least_ amount of water necessary will provide the maximum
amount of power as water vapour displaces oxygen. It's better to
have tiny droplets of water until the valve closes for compression.

> exactly what it "does" is still a mystery to me & the topic of a
> major debate that I don't think that we have got to the bottom of.

Evaporating the droplets in-cylinder doesn't reduce the total oxygen
present even when the droplets evaporate and absorb energy during
compression (six to seven times the amount of heat as for the same
mass of gasoline).  The water vapour acts as a "buffer" to the flame
front, not only obstructing it at a molecular level, but also to
reduce hot spots by absorbing some of their heat.

The Gasoline FAQ indicates the degree to which water content in the
air (humidity) reduces an engine's Octane number requirements. Order
of magnitude is 4 g water per kg of air reducing ONR by one point.
(The relationship is not entirely linear.)

With a high charge temperature and without becoming saturated, one
could add 40 to 60 g of water per kg of inlet air, depending on
initial ambient conditions. That's an AWR of between 25:1 and 16:1
for an ONR of between 10 and 15 points.

Too much water and the flame front slows too much as the reagents
take longer to "find" each other, resulting in less torque.
Determining what is "too much" will take some tuning time. Accurate
knock detection and some means of measuring torque under controlled
loads are a distinct advantage.

Well, that's one theory anyway.
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