Good Point Brad,
this all stems from the bernoulli rule:
The Bernoulli Rule is basically a spin-off of the conservation of energy principal. The rule basically says that in order to have equal energy states air at low velocity high pressure on the outside of the carburetor inlet will be at an equal energy state to the air inside the carburetor that has High Velocity and Lower Pressure. This Equal energy state exists in the whole inside of the carburetor just inside the velocity stack and not at just the spraybar. There are some “high end” carbs that use this principal again inside the carb to create small areas within the low pressure zone with incrementally lower pressures and higher velocities.
So to some extent, the same thing is being said, just in different ways.
When one speaks in terms of fluid mechanics, the moving force is difference in pressure, not air velocity. One of the basic premises of fluid mechanics is that matter flows with a constant energy state naturally from to Low Pressure regions from High Pressure regions. Meteorologists, engineers, and physicists generally use the terms of pressure as the motivating element behind the movement of mass.
Atmospheric pressure exists everywhere and is around 14psi depending on altitude and weather.
Lets perform a little class experiment regarding this assertion disregarding the effects of gravity:
When a motor is first started the fuel cell is at atmospheric pressure but not for long because it increased by backpressure from the exhaust side of the motor. When the motor is running at some steady state the pressure in the fuel cell is actually higher than atmospheric pressure, and would flow right out of the fuel line if you disconnected it from the carburetor (removed it from the high velocity air). If you disconnected the fuel line from the carb it would be connected to the atmosphere and the atmosphere is at Atmospheric pressure. Fuel would continue to flow into the atmosphere and atmospheric pressure would not push it back. In other words, fuel would flow out of the fuel line until the fuel cell is at atmospheric pressure. When the fuel cell is at atmospheric pressure the flow would stop. Another way to state this is that Atmospheric pressure does not push the fuel into the carburetor assembly.
The Mathematics of the Bernoulli Principle
The Bernoulli Principle is a statement of energy balance. It correctly states that for certain conditions (steady flow, no friction and incompressible fluid), the sum of the thermal, kinetic and gravitational energies is constant at all locations. Thus, for fluid moving through a system of pipes of varying cross section, the fluid that moves through narrow pipes, moves fast and has low pressure while the fluid that moves through wide pipes moves slowly and has high pressure. The formula for this principle is:
ET + EK + EG = k
For systems that do not involve gravity change, this becomes
ET + EK = k
Thermal energy + kinetic energy is everywhere constant.
Now since ET = PV and EK = Mv²/2
PV + Mv²/2 = k
The product of Pressure and Volume plus 1/2 the product of Mass and the square of velocity is everywhere constant.
So for flow from a large diameter pipe to a small diameter pipe within a closed system, velocity (v) increases so pressure (P) falls. Students often interpret Bernoulli's Principle to say that that fast flow "causes" low pressure. In practice, the opposite is true since it takes a pressure gradient to "cause" fluids to flow. Continuing,
Dividing both sides by volume,
P + dv²/2 = k
and, rearranging,
P = k - dv²/2
So, an increase in velocity indicates a decrease in pressure.
So back to how this applies to the supercharger:
When the induction port of the engine is closed, the Supercharger surcharges the pressure of the air in the intake manifold to a pressure above atmospheric pressure. At this point there is no flow in the carb and the fuel will flow backwards toward the fuel cell until there is flow in the carb. It appears that the proper way to choke this system would be to choke off the exhaust, so that when it is choked the supercharger will surcharge the fuel system enough to provide pressure that is equal to the pressure in the intake manifold when the induction port is closed. Therefore, there would be sufficient pressure gradient to provide fuel flow in the carb when the intake manifold pressure drops because the induction port is open.
In Summary:
This supercharger will probably work to some extent, but would probably be best suited for the smallest motors since the pressure gradients are very small. The added load from moving parts would probably largely diminish any performance improvements in the motor. Larger systems would probably have a problem with popping fuel lines and leaking fuel systems. Just about every time I go to the pond I break something before returning home. It seems like this would be just another thing to break.
:huh:
