Experimental Characterization of DI Gasoline Injection Processes 2015-01-1894

This work investigates the injection processes of an eight-hole direct-injection gasoline injector from the Engine Combustion Network (ECN) effort on gasoline sprays (Spray G). Experiments are performed at identical operating conditions by multiple institutions using standardized procedures to provide high-quality target datasets for CFD spray modeling improvement. The initial conditions set by the ECN gasoline spray community (Spray G: Ambient temperature: 573 K, ambient density: 3.5 kg/m³ (∼6 bar), fuel: iso-octane, and injection pressure: 200 bar) are examined along with additional conditions to extend the dataset covering a broader operating range. Two institutes evaluated the liquid and vapor penetration characteristics of a particular 8-hole, 80° full-angle, Spray G injector (injector #28) using Mie scattering (liquid) and schlieren (vapor). Diffused back-illumination (DBI) imaging, which is the ECN standard liquid length diagnostic, was also used to provide a reference for the Mie scatter measurements. In addition to imaging the full liquid field, the DBI measurements included long-distance microscopy collection to permit characterization of near-nozzle, end-of-injection details. Interpretation of plume-to-plume variation was assisted by nozzle geometry measurements performed using optical microscopy and x-ray tomography.

Results indicate that global spray parameters such as liquid and vapor penetration as well as spray angle are similar between the two facilities. The spray development and mixing is largely affected by charge gas conditions (mainly density). For instance, under the standard Spray G density, the individual plumes remained separated until the end of injection, while at higher ambient densities the plumes merged together. Spray development results, together with spray mechanical patternation supported the correlation with measured nozzle internal geometry. Long-distance microscopy measurements showed that the main flow was attracted toward the injector centerline after the end of injection, supporting the convergence of the plumes as observed in the spray angle measurements.