Published on March 12, 2014
Exhaust Noise Control Locomotive 2815 Redesigning the coffin muffler to address low frequency noise problems 1/8/2013
ARTC’s EPL 3142: “Almost a third of all rail noise complaints received by the Environment Protection Authority (EPA) between 2007 and 2011 were generated by pass by noise from locomotives. For this reason the EPA considers the ongoing monitoring and management of locomotive noise to be a critical component of environmental regulation on the NSW rail network.”
EPA Noise Limits for Locomotives new to the NSW Network Operating Condition Speed and Location of Measurement Noise Limit at 1.5 m above ground level Idle with compressor radiator fans and air conditioning operating at maximum load occurring at idle Stationary 15 m contour 70 dB(A) Max All other throttle settings under self load with compressor radiator fans and air conditioning operating Stationary 15 m contour 87 dB(A) Max 95 dB Linear Max All service conditions As per Australian Standard AS2377-2002 87 dB(A) Max 95 dB Linear Max
Back in 2006… Notch Setting Level @ 15m Noise Limit Notch 4 & 5 83 dB(A) Max 104 dB Linear Max 87 dB(A) Max 95 dB Linear Max Notch 8 85 dB(A) Max 102 dB Linear Max 87 dB(A) Max 95 dB Linear Max
In 2012, with modified transition muffler… Notch Setting Level @ 15m Noise Limit Notch 8 87 dB(A) Max 99 dB Linear Max 87 dB(A) Max 95 dB Linear Max
Locomotive Passby Noise • Four examples of passby noise - different locomotive classes • All recorded at 7.5 m from the track, same direction of travel, same location • Uncontrolled test – varying speeds and number of locomotives
Starting Point – Loco 2815 • A-weighted noise compliant with EPA limits • Linear noise levels up to 4 dB above EPA limits (in Notch 8) • Linear levels dominated by 50 Hz component – low frequency emissions of particular concern to the EPA • Overall, noise emissions similar to many locomotives operating in NSW
Contents • Sound intensity testing • Transmission loss measurements • Coffin muffler design • Scale model prototypes • Full scale cold testing • Hot testing • Repeat of stationary type testing
Sound Intensity Testing • Scan locomotive to identify source of noise emissions in different frequency bands
Sound Intensity Contours 50 Hz
Transmission Loss • Aim to establish performance of existing muffler – both the coffin muffler and the previously modified transition muffler • Measure at exhaust height, 3m from outlet – Original transition muffler, original coffin muffler – Modified transition muffler, original coffin muffler – Transition muffler removed (ie, no transition or coffin muffler)
Transmission Loss Measurements
Transmission Loss Results • With original transition – particularly poor performance below 100 Hz – noise emissions in several frequency bands (including 50 Hz) amplified rather than attenuated. • With modified transition – performance remained poor at low frequencies. – overall linear attenuation of 7 dB – attenuation of 0 dB at 50 Hz
Coffin Muffler Design Inputs • Drawings of original muffler • Information on muffler internals • Exhaust flow rates • Exhaust temperatures
Resources available • 1 x spare muffler • 1 x spare original transition • 1 x modified transition • 1 x locomotive (2815) • Support from Aurizon
Design Approach • Decision made not to use FE software • Theoretical design (calculations) • Scale model testing for design optimisation (scaled for size and temperature) • Cold testing with adjustable components (results scaled for temperature) • Hot prototype testing
Full scale cold testing
Scale model testing
Cold testing – Tuning
Full Scale Prototype
Final Prototype Design • Volume increased by 60% – increased height of muffler body – take advantage of available space – width and length maintained • Double expansion chamber • Tuned quarter wave chambers targeting 50 Hz frequency component
Prototype Hot Testing • Initial hot testing took place on 11 March using identical 3m microphone positioning to that employed for the transmission loss tests of the original muffler.
Hot Testing Results
Hot Testing Results Parameter Original Level @ 3m New Level @ 3m Increase in Attenuation A-Weighted Overall LAeq 96 dBA 96 dBA 0.0 dB Linear Overall Leq 107 dB 101 dB 5.4 dB 25 Hz 1/3 Oct Band Leq 101 dB 84 dB 16.1 dB 50 Hz 1/3 Oct Band Leq 101 dB 83 dB 18.1 dB
Hot Testing Results • Overall linear noise levels reduced by 5 dB • No change in A-weighted levels • Major reductions in tonal noise in Notch 8: – 18 dB reduction in the 50 Hz band – 16 dB reduction in the 25 Hz band
Before and after – recordings at 3m from exhaust outlet
In 2013, with redesigned coffin muffler… Notch Setting Level @ 15m Noise Limit Notch 8 86 dB(A) Max 94 dB Linear Max 87 dB(A) Max 95 dB Linear Max
Conclusion • The EPA has subsequently approved this locomotive class (re-badged as the 3200 class) for use in NSW: “Based on the information provided, the EPA considers that the noise performance of the 3200 class locomotive is consistent with current best practice in NSW.”
Thanks • Steve Brown – design lead • Evan Brown – prototyping assistance • Aurizon – Matt Pearce and Ray McCabe
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Briony Croft, SLR Consulting Australia: Exhaust noise control locomotive 2815 – Redesigning the coffin muffler to address low-frequency noise problems.
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