The basic jist of the problem is that we're building a single cylinder engine that runs off an air compressor (this is at uni, and is hidden so I can't check to see if has a flow rate written on it), and it goes through a 4mm diameter opening into a closed cylinder when a valve is opened. I asked my professor for the flow rate of the air-compressor, and all he told me was that the air is at 80 psi, and it flows through a 4mm circular opening. So I'm assuming that it is possible to attain a very rough estimate of flow velocity knowing just these two pieces of information (that is assuming no pressure drop, friction etc).

Now I haven't studied thermodynamics comprehensively or have done a fluids unit, so I don't have all that much background knowledge to rely on to calculate. I've tried applying Bernoulli's equation to find the flow velocity (both the incompressible method by assuming an isentropic flow and the compressible flow variant on wikipedia) but they are both giving me velocities in the realm of 1000 m/s which is ridiculous.

If there is any way I can calculate it that would be helpful, because it would mean I could apply it to the flow of once the exhaust valve is opened (which I can't measure because it wont be built in time for the report next week). Otherwise I'll have to measure it roughly and guess the exhaust flow for the report.

Thanks in advanced.