Quote:
Originally Posted by greasemonkee
True vacuum? you mean continuous vacuum?
I would expect to see a cyclic vacuum taking place (under lower than ambient manifold pressures), similar to a sine wave; the gauge should be an average pressure reading, but then again the velocity of the air at the injector port itself makes it more complex.
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EDIT: This is "as I understand it". I welcome other input, suggestions, or data which suggests otherwise.
No, I mean true vacuum. The vacuum in the manifold is only readable because of the velocity of the intake flow, which is why the vacuum reading in your manifold actually could change depending on where you plumb the line, although most gauges won't register the change (which is going to be fractional, at best).
Vacuum can only truly occur in a sealed container which does not contain atmosphere, which means that since an intake manifold constantly has some amount of air in it, there is no actual vacuum, only a reduction in ambient pressure of the volume of air present.
If you checked the vacuum at each port of each cylinder, you would see the cyclic effect you're suggesting, but only for milliseconds per revolution, right before the air has a chance to react and begin moving into the cylinder.
I guess the point is that induction is not vacuum, by definition.
The flow of air through the manifold would prevent the pressure of the fuel from being reduced to the point where it boiled, except maybe for a few milliseconds until it actually got to the airstream, at which point it would instantly become liquid again.
Interesting to note -
The largest percentage of the noise from submarines in motion comes from steam, which is produced in bubbles which follow the trailing edges of the propeller. The bubbles "pop", which creates the noise signature that other submarines and radar/sonar systems recognize as a submarine.
The bubbles are a low-pressure zone in the wake of each prop blade. The pressure is low enough that water boils instantly in that area, then as it cools via the surrounding water and pressure change, it changes back to liquid and the bubble formed makes a pop noise.