|MadSci Network: Engineering|
The following Web page has a few good pictures of what you are asking about: Fluid Dynamics The venturi effect happens because fluid pressure drops as the fluid speed increases. If you force a fluid (for example: air or water) down a tube with a narrowing in it, the fluid will move faster through the narrow part. When it starts to move faster the pressure drops. In in internal combustion engine this is commonly used in carburetors to mix fuel with air. Air is sucked in the mouth of the carburetor and flow through the "throat" or narrow part of the carburetor. When it does this the pressure drops below the pressure of the air outside and sucks fuel from a small hole in the throat (the fuel "jet") with the fuel sprayed into the air, the mixture travels through the intake manifold into the cylinders where it is burnt for energy. A vortex is very easy to see. When you drain water from a sink there is a depression that forms over the drain. The water swirls around this depression as it travels to the drain. This swirling is caused by the Coriolis force from the rotation of the Earth. The vortex effect and the venturi effect are used together in Internal combustion engine to improve efficiency by making the fuel and air mix better in the throat of the carburetor, and as the fuel-air mixture moves down the intake manifold to the cylinder. "Swirl" a form of vortex, is used inside the cylinder to make the combustion of the fuel-air mixture occur smoothly and predictably. This increases efficiency and make the engine run smoothly. So, the vortex and venturi effects don't really help the gas move faster, but they encourage fuel and air to mix better giving a more even and efficient fuel burn.
Try the links in the MadSci Library for more information on Engineering.
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