The 4000 class locomotive is one of the latest additions to the Queensland Rail (QR) fleet. This locomotive is diesel electric with 2424 kW gross power. During the initial commissioning of this new piece of rolling stock a variety of noise testing was conducted to verify that the noise levels emitted did not exceed the specified limits under all operating conditions. It was found that during stationary noise testing the specified limit of 85 dB(A) according to Australian Standard was exceeded when the engine was in maximum throttle and both cooling fans were on high speed. The noise levels measured were 91.8 dB(A).

The aim of this study was to develop a method of noise reduction for cooling fans fitted to the 4000 class locomotives. This study focused on eliminating the noise at its source. The source of the noise from fans is directly proportional to the blade bypass frequency. Due to the turbulence created at the blade tip, this is where the majority of noise is generated. The effect of directing air away from the blade tip at the inlet was tested. Methods of testing of cooling fans were devised in order to quantify the noise reduction achieved by different modifications. It was found that by reducing the amount of air passing across the fastest moving part of the blade, the noise level could be reduced to within allowable limit of 85 dB(A). Modifications put forward in this study can be implemented during the routine maintenance of the locomotives.