Interior Flow and Formation of Plain Orifice Sprays

Doktorsavhandling, 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 the 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 signifcantly simplifed 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 interior 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.