Experimental Studies of Primary Break-up of Diesel Engine Fuel Injector Sprays

Licentiate thesis, 2014

This thesis will focus on experimental studies of primary breakup of pressure-atomized sprays. The industrial application that this thesis will address is fuel sprays in modern Diesel engines, and so the focus will be sprays emitting into relatively slow-moving, high pressure, high-temperature gases. The density of the ambient gas has been shown to affect primary breakup more than the temperature, except in some special cases which will be covered later on in this thesis. It stands to reason, then, that the primary break-up physics of Diesel fuel sprays should be similar to sprays emitting into dense gases at room temperature. Knowledge of the primary break-up of Diesel sprays can also be gained from studies of sprays emitting into atmospheric gases, so long as the Weber number is sufficiently high. This thesis will examine experimental studies of these more simplified sprays, with an emphasis on trans-illumination imaging studies, which provide most of the understanding of primary break-up of pressure atomized sprays that currently exists. This thesis will also provide a cursory overview of a few other measurements that provide quantitative data relevant to multiphase flow descriptions. The state of the art in CFD simulations of sprays under realistic Diesel engine conditions will also be covered, albeit in a skeletal manner. Lastly, this thesis will summarize the author’s contribution to the state of knowledge concerning primary breakup of Diesel engine fuel sprays. The entire thesis will be framed and structured by the challenge of studying primary break-up of fuel sprays found in modern direct-injection compression-ignition internal combustion(IC) engines. Sprays at lower Reynolds and Weber numbers will be discussed because of their role in informing numerical and conceptual models of primary break-up of more aggressively atomizing sprays.