Low Air Compressor CFM Still Works?

AI Thread Summary
To test a mach 2 ramjet, a requirement of 50-72 CFM is noted, while the available compressors only provide 2 CFM. The possibility of running a 25 CFM air compressor at 50 CFM for short bursts is questioned, along with how to calculate the operational duration above the required CFM. Isentropic equations indicate a necessary tank pressure of approximately 115 psi for the desired outlet. The discussion highlights that typical air compressors do not allow for variable CFM settings, and suggests using a large reservoir tank to store and release compressed air quickly. Understanding the CFM rating as a measure of mass flow is also emphasized.
yangshi
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Halfway through my thesis on a mach 2 ramjet, and I unfortunately realize that I need 50-72 CFM to test it. The only ACs I have are 2 CFM portable pancakes. Is it possible to run say a 25 CFM AC at 50 CFM for a short period of 10-60 seconds? Is there a quantitative way to find how long the AC will last above the required CFM?

I used isentropic equations to find that the required tank pressure is ~115 psi for mach 2 outlet, if that helps...
 
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Are you using "CFM" as a measure of volume flow or mass flow? According to http://www.truetex.com/aircompressors.htm the CFM rating of an air compressor is a measure of mass flow.

I don't know how you can run a typical air compressor at a variable CFM. I suppose the flow rate varies as you make it work against more and more pressure, but haven't seen any compressors where you can set the CFM to a specific value.

Can you get a large reservoir tank and slowly fill it with compressed air, then release the air suddenly?
 
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