Active Noise Control Technique for Diesel Train Locomotor Exhaust Noise Abatement.

An original prototype for train locomotor exhaust noise reduction (electronic muffler - EM) is proposed: the system is based on an active noise control technique. An acoustical measurement campaign has shown that locomotor exhaust noise is characterized by very low frequency components (less than 80 Hz) and very high acoustic power (up to 120 dB). A custom EM, characterized by high acoustical efficiency at very low frequencies has been designed and realized at Perugia University Acoustic Laboratory; it has been installed on an italian D.245 train locomotor, equipped with a 500 kW diesel engine. EM has been added to the traditional passive muffler. Very low transmission losses are introduced by EM because of its particular shape; thus, engine efficiency does not decrease. Cancelling noise is generated by means of DSP based numerical algorithm. Disturbing noise and cancelling noise destructively interfere at the exhaust duct outlet section; outgoing noise is thus reduced. The control system reduces exhaust noise both in steady and unsteady engine regime. Measurements results have shown that EM introduces up to 15 dB noise abatement in 31.5-63 Hz frequency range.