CNG compressor capacity

First, pay close attention to your units of measure. In the equation you provided, you are calculating the ideal displaced volume of the compressor. This is not the flow capacity. what you really need are the volume flow rate and mass flow rate. For gas compression, I suggest you use standard temperature and pressure to report flow rate.

Q= (L*A*N/1728)*VE*(Pi/Ti)*(Tref/Pref)

Where,

Q= capacity (standard cubic feet per minute)

L= stroke length (inches)

A= Area of piston (square inches)

N= no. of revolutions per minute

1728 = no. of cubic inches per cubic foot

VE = volumetric efficiency (compressor manufacturer supplied)

Pi = absolute inlet pressure (psia)

Ti = absolute inlet temperature (Rankine)

Pref = standard pressure usually atmospheric pressure at sea level (14.696 psia)

Tref = standard temperature usually 60F (520 Rankine)

The volumetric efficiency changes with the inlet pressure and pressure ratio and is usually determined through testing. For small compressors, the end user can determine this with a proper closed circuit test loop with good quality flowmeters, pressure sensors, thermocouples and speed measurement devices. For most size compressors, the manufacturer can provide you with that information. Most manufacturers have computer programs which will calculate this for you, as well as other imprtant performance criteria for their own products.

For reciprocating compressors running near atmospheric temperature and pressure at the inlet and discharge pressures about 6 to 10 times the inlet pressure, the volumetric efficiency can be about 90% to 95%.