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|Title: ||An optical investigation into the effect of fuel spray, turbulent flow and flame propagation on DISI engine performance|
|Authors: ||Rimmer, John E.T.|
|Issue Date: ||2011|
|Publisher: ||© J.E.T. Rimmer|
|Abstract: ||There is currently considerable interest in new engine technologies to assist in the
improvement of fuel economy and the reduction of carbon dioxide emissions from
automotive vehicles. Within the current automotive market, legislative and economic
forces are requiring automotive manufacturers to produce high performance engines
with a reduced environmental impact and lower fuel consumption. To meet these
targets, further understanding of the processes involved in in-cylinder combustion is
required. This thesis discusses the effect of fuel spray structure, flame propagation and
turbulent flow on DISI engine combustion. To investigate these flow processes within
the fired single cylinder Jaguar optical engine a number of optical measurement
techniques have been used, including high speed laser sheet flow visualisation
(HSLSFV) and high speed digital particle image velocimetry (HSDPIV).
Results obtained from dual location flame imaging has provided further understanding
of the relationship between flame growth, engine performance and cycle-to-cycle
variation. Detailed correlation analysis between flame growth speed and engine
performance parameters demonstrated that it is the flow conditions local to the spark
plug at the time of spark ignition that have greatest influence on combustion. It was
also demonstrated that further gains in engine performance and stability can be
achieved by optimising the fuel injection timing.
The temporal and spatial development of flow field structures within the pent-roof
combustion chamber at the time of spark ignition were quantified using HSDPIV.
Decomposition analysis of the raw velocity data enabled the relationship between
specific scales of turbulent flow structure and engine performance parameters to be
investigated. Correlations between the high frequency turbulence component and
pressure derivatives are shown, demonstrating that it is the frequencies of motion
>600 Hz that have the greatest influence on early flame development and therefore
rate of charge consumption, engine performance and combustion stability.
A series of double fuel injection strategies were devised to investigate the potential for
using the fuel injection event to influence flow field structures within the cylinder.
Results demonstrated that while the fuel injection event had limited impact on bulk
flow structures, there was an increase in turbulence post fuel injection, depending on
the timing of the second injection pulse. However, this advantage was not sustained
throughout the compression stroke to have significant impact on combustion.
The final stage of research investigated fuel spray structure, flame propagation and
charge motion at fuel impingement locations, comparing a single and triple injection
strategy. A triple injection strategy is proposed that results in an improvement in the
levels of fuel impingement on combustion chamber walls and a reduction in the high
luminosity regions within the flame. Consequently, adopting the multiple injection
strategy highlighted the potential for reducing unburned HC emissions and soot
formation within homogeneous charge DISI engines.|
|Description: ||A Doctoral Thesis. Submitted in partial fulfillment of the requirements for the award of Doctor of Philosophy of Loughborough University.|
|Appears in Collections:||PhD Theses (Mechanical, Electrical and Manufacturing Engineering)|
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