PD compressor or ICE engine, gas pulsation noise, parallel serial noise suppression
Positive displacement (PD) compressors and internal combustion engines (ICEs) are major energy consumers. For example, a typical US household may have as many as 7 compressors (2 in house AC, 2 in auto AC, 1 each for refrigerator or freezer or shop compressed air) and 4 ICEs (2 in auto, 1 each for lawn mower and auxiliary power generator). However, they both generate high amplitude pulsating pressures1 (up to 180-200 dB) and discharge flows that demand a silencer or muffler to suppress the noise but leads to high energy costs: up to 5-7% shaft power for PD compressors and up to 2-5% gasoline or diesel consumption for ICEs. Growing global demand for higher efficiency and lower noise for these systems is conflicting with the governing rule of serial muffling employed for the past 100 years: “more noise reduction, more back pressure losses or larger sizes”. No current technology could meet both demands simultaneously due to the limitation of the current serial noise suppression methodology. The primary goal of this paper is to demonstrate Shunt Pulsation Trap (SPT) - a parallel noise suppression method that will overcome this limitation and is capable of getting the pulsating noise under control with little back pressure loss and compact size. The SPT technology involves modifications to a standard PD compression cycle from a serial mode, that is, treats or dampens the noise generating source ∆P (Poutlet-Pcavity) after discharge, to a parallel mode before discharge. Thermodynamic analysis and earlier tests on a Roots-type compressor with SPT indicate this novel noise suppression concept yields a substantial saving in shaft power (5-16%) while remaining compact compared with a serial silencer. Parallel and serial noise suppression rules are summarized and applied to various PD type compressors and ICEs.