compressor or engine, gas pulsation control, pulsation trap
Gas pulsations commonly exist in HVACR, energy and automotive industry. They are believed to be a major source for system inefficiency, vibrations, noises and fatigue failures. It has been widely accepted that gas pulsations mainly take place at the discharge side of a positive displacement (PD) type compressor such as a screw, scroll or internal combustion engine. The pulsation magnitudes, ranging from a fraction to a few bars, are especially significant at off-design conditions of either under-compression (UC) or over-compression (OC). Traditionally, a serial pulsation dampener, often a reactive type silencer, is connected after the compressor or engine discharge. It is capable of reducing pressure pulsation by 10 plus fold; or 20 plus dB. However these dampeners are bulky and impose sizable back pressure losses. This paper discusses an alternative method, a shunt pulsation trap (SPT), using a parallel configuration, which tackles the gas pulsations before the compressor or engine discharge. The SPT method is based on the shock tube theory  that characterizes the nature of gas pulsation as a composition of non-linear waves, compression wave (CW) and expansion wave (EW) and induced fluid flow (IFF). The theory also predicts that the dominant source of gas pulsation is a direct result from the sudden discharging process under UC or OC condition. Two prototypes, 75 HP and 350 HP Roots type blowers, were built and tested with and without SPT. The experimental results partially validate the new theory and also indicate a 10 plus fold; or 20 plus dB pulsation reduction by using SPT under different load and speed conditions without suffering any back pressure losses.