Interior Flow and Formation of Plain Orifice Sprays
Doctoral thesis, 2016
This thesis will summarize recent experimental observations of spray formation in highly atomizing plainorifce sprays, the kind commonly produced by fuel injectors in compression ignition internal combustion
engines. Two special interactions will be addressed in detail: primary atomization under elevated ambient
pressures and temperatures and orifce
ow effects on primary atomization. The thesis will progress
analogously to the physical progression of the
ow from a Lagrangian reference frame, beginning with
ow in the sac volume, proceeding to the orifce
ow, and then moving out to the spray. As these
subjects are reviewed, relevant theory in
uid mechanics and thermodynamics will be presented, which will,
among other things, identify and explain non-dimensional parameters frequently used in experimental
studies. Even further specialized topics with much broader relevance, namely turbulence, cavitation,
and other interesting phase transformations, will be covered with emphasis because these are ongoing
research areas. This review focuses on past experimental work, ranging from fundamental studies using
ow rigs to studies where industrial injectors were used with little to no modifcation.
Intermittently, relevant results from spray formation simulations will be included. Finally, the author
will summarize his contribution to the state of knowledge in these areas.
Although the detailed physics covered in this thesis have a wide range of practical applications, this
thesis focuses on the orifce
ow and primary atomization of sprays used in internal combustion engines
(ICE) to mix liquid fuel with air. This problem has served as the main motivation for these studies
because it has been identifed as a mechanism for reaction control in these engines. The detailed physics
of this multiphase
ow are yet to be understood fully on all relevant scales to the point where a fully
exible, predictive engineering tool can be created.
The author's work has addressed the controversy surrounding dense-
uid mixing, together with the
effect of internal
ow on spray formation. Using a novel transparent injector designed by the author, the
ow of a high-pressure marine Diesel engine fuel injector was investigated simultaneously with
the spray formation region at injection pressures much closer to that of a real injector than studies in
the past, and the effect of cavitation specifcally on spray formation was captured using high-speed video
and Ballistic Imaging (BI).
BI was also used to capture the formation region of fuel sprays from commercial injectors under a
range of ambient conditions, with a variety of single-component fuels and a commercially available diesel
fuel. Although a structural change in the BI was seen for butanol at the most extreme case, a more
detailed study is needed to determine the
uid state evolution and the effect of the ambient conditions.