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|Title: ||Numerical and physical analysis of liquid break-up and atomisation relating to pressure-swirl gasoline direct injection|
|Authors: ||Heather, Andrew|
|Keywords: ||Gasoline Direct Injection|
Computational Fluid Dynamics
|Issue Date: ||2007|
|Publisher: ||© Andrew Heather|
|Abstract: ||This thesis presents detailed fuel spray investigations relating to an automotive Gasoline
Direct Injection (GDI) pressure-swirl injector, employing a combination of numerical and
physical analyses. The emphasis is placed on the near-nozzle in recognition that all
later flow processes are dominated by this critical region. To enable the technology to
maximise its potential, it is essential to further our understanding of the fundamental flow
physics that govern the injection process, which remain largely unknown.
The complexity of the spray process has led to many avenues of research. Simplified
models are particularly suitable for parametric studies, allowing fast computation of some
of the most important design parameters, such as nozzle discharge coefficient, cone
angle and initial velocity. More complex methods such as Computational Fluid Dynamics
(CFD) offer significantly more detail including the temporal and spatial evaluation of the
flow field and fuel distribution, but at the cost of often lengthy computational time, and the
need to tune models against physical evidence. Unfortunately none are able to describe
all aspects of the injection event simultaneously.
A considerable body of existing experimental data gathered under atmospheric conditions
has been condensed and carefully presented to provide a comprehensive picture
of injector operation. This comprises global spray performance data, spray imaging, and
droplet velocity and size maps as a function of time after the Start Of Injection (SOl).
These serve to provide a means to develop physical models and to correlate model predictions.
Particular attention is drawn to the challenges faced by numerical methods to
successfully predict the complex spray behaviour.
A fundamental computational study employing the Volume Of Fluid (VOF) method describes
droplet break-up under controlled conditions. By varying the Weber number of
the flow the expected break-up mechanisms are recovered, and the numerics and case
set-up tuned to offer a practical balance between the resource burden and solution accuracy.
This paved the way to a detailed 3-D transient analysis of the near-nozzle region of
a pressure-swirl injector. Computed results clearly identify the consecutive phases of the
fuel spray development, from the initial unsteady jet through to the stable, swirling hollow
cone formation. Comparison with experimental measurements revealed that the computational
approach is able to capture the main qualitative features of the spray process.|
|Description: ||A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.|
|Appears in Collections:||PhD Theses (Aeronautical and Automotive Engineering) |
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