Elevated engine noise at back of commuter bus Wenfa Ng figshare 02 Oct 2016.pdf (272.69 kB)
Elevated engine noise at back of commuter bus
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.