The Effects of Injector Temperature on Spray Characteristics in Heavy-Duty Diesel Sprays 2018-01-0284
This work investigates the impact of injector temperature on the characteristics of high-pressure n-dodecane sprays under conditions relevant to heavy-duty diesel engines. Sprays are injected from a pair of single-hole diesel injectors belonging to the family of “Spray C” and “Spray D” Engine Combustion Network (ECN) injectors. Low and high injector temperature conditions are achieved by activating or de-activating a cooling jacket. We quantify spray spreading angle and penetration using high-speed shadowgraphy and long-distance-microscopy imaging. We evaluate differences in fuel/air mixture formation at key timings through one-dimensional modeling. Injections from a cooled injector penetrate faster than those from a higher temperature injector, especially for an injector already prone to cavitate (Spray C). When uncooled, Spray C exhibited a time-varying spreading angle at early times during the injection event, which exacerbates the reduction in initial penetration rate relative to the cooled injector. Changes in fuel density alone cannot account for the observed trends and we show that implementing a transient spreading angle in the model (guided by the time-sequenced images) is an effective solution to match experimental penetration characteristics. Time- and axially-resolved radial mixture fractions derived from the model reveal that failure to account for early spreading angle transients and their impact on penetration and mixture formation leads to erroneous mixture fraction distributions at key timings associated with first and second stage ignition. Such oversights could lead the community toward incorrect model calibrations.