Elevated engine noise at back of commuter bus
Creators: name: Ng, Wenfa
Publisher: name: figshare
Year: 2016
Subjects: subject: Mechanical Engineering
subject: FOS: Mechanical engineering
subject: FOS: Mechanical engineering
subject: 59999 Environmental Sciences not elsewhere classified
subject: FOS: Earth and related environmental sciences
subject: FOS: Earth and related environmental sciences

description: Noise is discomforting at best and may be hazardous to hearing when exposed to at high intensity for long periods of time such as in the workplace. Public commuter bus is one of the main forms of transport for people around the world, but what is the level of noise exposure in the bus, especially at the back of the bus where the engine is typically located? Using an Android smartphone equipped with the Google Play Store app, Science Journal, the noise environment at the back of a public bus in Singapore was measured through the microphone of the smartphone. During the 10 minutes’ measurement, the bus was coasting through various types of road environment in Singapore from the initial high speed cruise along an expressway to stop and go traffic within a housing estate, and the bus engine was the dominant source of noise. Analysis of the data revealed that the maximum intensity of noise was 83 decibel absolute (dB), with the lowest at 63 dB, and the average at ~ 73 dB. Looking at the data more closely revealed that engine noise was highest during high speed travel (~ 78 dB), while the engine hummed at ~ 68 dB during a full stop. As speed increased and the automatic gear box of the Mercedes Benz Citaro bus shifted up to a higher gear, there was noticeable increase in noise. Although a typical commuter ride on a bus is short, and exposure to elevated engine noise for short periods is not harmful, the same cannot be said for exposure to noise in excess of 80 dB for prolonged periods. From a different perspective, engine noise outside of the bus was also measured at a bus stop where 4 buses sequentially enter and leave the bus bay. Distinct spikes in sound intensity from the basal level of ~ 60 dB marked the revving up of the bus engine as it accelerated from the bus bay. Overall, noise levels detected at bus stop (highest recorded for all 4 buses was above 80 dB) corroborated those detected onboard the back of a bus, and highlighted a source of noise pollution at the back of a relatively new air conditioned bus from a reputable manufacturer, which in addition to degrading the experience of the commuter ride, may also impact on his/her hearing in the long term. Possible causes for the higher than expected engine noise may be engine damage or poor maintenance leading to degradation of engine moving parts. Another possibility could be miscalibration of parameters in the engine control unit software that resulted in a fuel rich mixture, which led to engine knocking; or the dys-synchronization of fuel introduction and ignition leading to premature explosion of fuel and air in the combustion chamber that resulted in severe knock on the engine’s pistons. Finally, poor fuel choice of low octane ranking is a common cause of engine knocking and noise, a factor that could not be discounted for. Collectively, elevated engine noise in public bus highlighted one area where the commuting experience could be improved, and a potential safety concern requiring immediate action, given the health impacts of excessive noise for prolonged periods as well as the possibility of an engine fire arising from elevated engine temperature due to miscalibrated engine control software or poor engine maintenance.