Ignition and Soot Formation/Oxidation Characteristics of Compositionally Unique International Diesel Blends 2019-01-0548

With the global adoption of diesel common rail systems and the wide variation in composition of local commercial fuels, modern fuel injection systems must be robust against diverse fuel properties. To bridge the knowledge gap on the effects of compositional variation for real commercial fuels on spray combustion characteristics, the present work quantifies ignition and soot formation/oxidation in three unique, international diesel blends. Schlieren imaging, excited-state hydroxyl radical (OH*) chemiluminescence imaging and diffused back-illumination extinction imaging were employed to quantify vapor penetration, ignition, and soot formation and oxidation for high-pressure sprays in a constant-volume, pre-burn chamber. The three fuels were procured from Finland, Japan and Brazil and have cetane numbers of 64.1, 56.1 and 45.4, respectively. In addition to ignition delay times, the high-speed OH* chemiluminescence imaging diagnostic yields the ignition location and the transient lift-off lengths. Time-resolved, two-dimensional soot optical extinction (KL) images were obtained using a diffused back-illumination extinction imaging diagnostic, and these images were integrated to yield the time-resolved total soot mass. Short injection durations were selected to allow imaging of the entire soot formation event and a portion of the oxidation process. Ignition delay variations among the three commercial diesel fuels are consistent with their respective cetane numbers. Differences in the chemical properties of the fuels are deemed responsible for the ignition variation, as penetration measurements for non-reacting sprays showed no significant variation in mixing characteristics. Variation of the soot mass produced by the different fuels is investigated by considering the soot trends against their respective lift-off lengths. Fuels containing more aromatics produce more soot for a given lift-off length. At low ambient temperature (850 K), lift-off length variations are large and have a significant impact on soot production characteristics, while at high ambient temperature (1000 K) variation in the lift-off length among the different fuels is small and compositional effects control soot production.