Ajovalasit, Marco (2006) Effect of fuel content on the human perception of engine idle irregularity. PhD thesis, University of Sheffield.
Abstract
This thesis describes a digital signal processing analysis of diesel engine idle vibration in
automobiles, and an analysis of the human subjective response to the idle vibration which occurs
at the steering wheel. In order to quantify the variations in the diesel idle vibration that can be
introduced by the engine technology, the vehicle, and the fuel type, a set of acceleration time
histories were measured at the engine block and at the steering wheel for two automobiles
equipped with 4-cylinder engines which had different injection systems and which operated under
different fuel conditions.
A combination of time domain, frequency domain and time-frequency wavelet-based analysis
were used. Both the continuous wavelet transform and the discrete orthogonal wavelet transform
were applied to the steering wheel acceleration time histories in order to analyse the statistical
variation in terms of both instantaneous variations, and the cycle-to-cycle variations which occur
across complete thermodynamic engine cycles. The combination of orthogonal wavelet transform
and time-varying auto-covariance analysis, performed across a complete engine thermodynamic
cycle, was identified as the most sensitive method for describing the statistical variation in diesel
idle vibration.
The second-order engine harmonic H2 was found to account for most of the vibrational energy
at the steering wheel when at idle. Amplitude modulation of the second-order engine harmonic H2
by the half-order engine harmonic H112 has been identified as the main characteristic of the
steering wheel signature of automobiles at idle. The steering wheel idle vibration produced by
different engines and different fuel conditions have therefore been described in terms of the
amplitude modulation depth "mil that characterises the idle waveform.
Four psychophysical response tests, determined by the combination of two test protocols and
two semantic descriptors, were performed. A model of the growth in the human subjective
response to diesel idle vibration has been proposed in which the response scale is a function of
the modulation depth parameter "mil. The model is defined over two regions of modulation depth.
For values of "m" less than 0.2, humans have been found to be unable to distinguish variations in
idle modulation. For values of "m" greater than 0.2, the human response grows as a power
function with respect to modulation depth. Based on the current findings, suggestions for future
research are also provided.
Metadata
Awarding institution: | University of Sheffield |
---|---|
Academic Units: | The University of Sheffield > Faculty of Engineering (Sheffield) > Mechanical Engineering (Sheffield) |
Identification Number/EthosID: | uk.bl.ethos.425574 |
Depositing User: | EThOS Import Sheffield |
Date Deposited: | 03 Nov 2016 12:14 |
Last Modified: | 03 Nov 2016 12:14 |
Open Archives Initiative ID (OAI ID): | oai:etheses.whiterose.ac.uk:15056 |
You do not need to contact us to get a copy of this thesis. Please use the 'Download' link(s) above to get a copy.
You can contact us about this thesis. If you need to make a general enquiry, please see the Contact us page.