Achieving sound performance through collaboration

Hushpak, Infrastructure, Noise Control

Our team at Hushpak Engineering loves a challenge.

Recently we were fortunate to work with a local rail carrier to develop a solution that would reduce the noise emissions of C Class locomotives. These locomotives are around 40 years old and are one of the loudest locomotives operating in NSW.

Working together with the carrier and with university acoustic specialists, we designed a state-of-the-art resonator muffler that reduced the noise emissions of C Class locomotives to levels comparable to modern mainline locomotives.

The following challenges were faced during the design process:

  • Limited space available in the locomotive engine bay meant that the final design had to be extremely compact.
  • The C Class locomotive engine incorporates a crankcase venting system that is very sensitive to changes in the exhaust outlet configuration.

The muffler was designed using advanced 3D finite element techniques that can predict the performance of a design over the frequency spectrum without having to resort to a design-build-test empirical process. This allowed us to achieve the greatest noise reduction whilst meeting specification limits for exhaust backpressure.

A detailed investigation of the operating parameters of the two-stroke diesel engine was required to ensure that the fitting of the muffler did not have any detrimental impacts on the venting of the crankcase to the exhaust stack or the overall locomotive performance.

Later model locomotives with mufflers fitted have an additional venturi device or ‘ejector’ installed to improve crankcase venting and avoid tripping the crankcase pressure sensor. An ejector unit from another locomotive was installed and trialled with the new muffler fitted. Following a modification to the internal ejector geometry, the locomotive was able to operate at full power on all notches and found to have crankcase pressure levels close to those with a standard exhaust stack fitted.

Acoustic testing of the final product has demonstrated success for the team. The installation of the custom-designed muffler recorded a decrease in noise emissions of up to 15 dB as shown in the following graph.

The installation of the custom designed muffler saw a decrease in noise emissions of up to 15 dB.

Congratulations to our Hushpak Engineering team for this outstanding achievement.

Hushpak’s muffl­ers are part of our wide range of noise control products that also includes low noise fans and acoustic louvres. If you are looking at ways to reduce noise output on heavy vehicles and mobile machines contact our team at Hushpak Engineering at (02) 4964 4000 or



Installation of the custom designed muffler on C Class locomotive

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