[Diy_efi] What is fuel atomization?

[Greg Hermann]

At 12:53 PM 7/30/02, Eric Fahlgren wrote:
>Dan D'Andrea wrote:
>>
>> What is fuel atomization?  I could not find an answer to this question using
>> google.
>
>Here's my working definition, contrasted with vaporization.
>
>Vaporization is the state change that occurs when a liquid becomes
>a gas.  State change to vapor usually requires quite a bit of energy,
>so the result is a gas much cooler than the original liquid.  (See
>http://intenz.gotdns.com/~eric/cars/turbo/glossary/water_injection.html
>for some numbers on vaporization of water.)
>
>Atomization is the shearing of a body of liquid into small particles
>of liquid, without significant state change.  These particles form a
>suspension in a gas, not a solution like evaporation produces.

To add a bit (??) more to that--

A source of energy is necessary to provide the heat necessary for
vaporization. ALSO-- vaporization is only possible up to the saturation
vapor pressure (at any given temperature),  to vaporize any more, the
overall temp of the mixture must be increased.

Vaporized fuel in the inlet tract:

1. Displaces a far greater amount of oxygen than the equivalent mass of
atomized liquid fuel.

2. Takes heat from the engine's cycle (usually via the back side of the
inlet valve) which might otherwise be used (in part) to produce useful
power.

3. Does NOT act as an internal coolant during the compression stroke.

4. Likely requires an increase in the inlet air temp (and corresponding
decrease in density and mass flow) in order for all the fuel to be
vaporized.

Atomized (liquid) fuel in the inlet tract:

1. Displaces a minimal amount of oxygen in the inlet tract.

2. Requires no increase in the inlet air temp.

3. Can act as an internal coolant during the compression stroke--the heat
absorbed by the vaporization of finely atomized fuel during the compression
stroke reduces the temperature rise of the mixture during the compression
stroke, and thus not only significantly reduces the negative work required
during the compression stroke, but also leaves the mixture at a lower temp
at the time of ignition, thus reducing the tendency to detonate.

Greg



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