Briony Croft, SLR Consulting Australia: Exhaust noise control locomotive 2815 – Redesigning the coffin muffler to address low-frequency noise problems

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