Ballistic Imaging and Scattering Measurements for Diesel Spray Combustion: Optical Development and Phenomenological Studies
Abstract
Ballistic imaging using a 15 picosecond pulse laser in high-injection-pressure diesel sprays is reported. An optical Kerr effect shutter, constructed from a CS2 liquid cell and activated by a 15 picosecond pulse at 1064 nm, produces effective 532 nm imaging pulses between 7 and 15 picoseconds. The performance of the imaging system is characterized using an Air Force target positioned before an optical cell filled with polystyrene spheres in a water suspension. The impact of spatial filtering, temporal filtering, and scattering path length on image resolution are reported. The technique is demonstrated by imaging the near-orifice region of methyl oleate and methyl butyrate sprays injected using a high-pressure single-hole fuel injector with direct comparison against simultaneous orthogonal shadowgraphy. The first successful demonstration of picosecond ballistic imaging using a 15 picosecond-pulse-duration laser in diesel sprays at temperature and pressure is also reported. This technique is used to image the near-orifice region (first 3mm) of diesel sprays from a high-pressure single-hole fuel injector. Ballistic imaging of dodecane and methyl oleate sprays are reported. Ballistic images of diesel injection at preignition engine-like conditions are reported. Dodecane was injected into air heated to 600¡C and pressurized to 20 atm. The resulting images of the near-orifice region at these conditions reveal dramatic shedding of the liquid near the nozzle, an effect that has been predicted, but to our knowledge never before imaged. These shedding structures have an approximate spatial frequency of 10 mm-1 with lengths from 50 to 200 microns. Several parameters are explored including injection pressure, liquid fuel temperature, air temperature and pressure, and fuel type. Resulting trends are summarized with accompanying images. The frequency doubled (532nm) and tripled (355nm) output of the Nd:Yag laser were converted to pulse sheets using cylindrical lenses to acquire cross sections of the spray interior. These sheets were then aligned to pass through the spray at varying offset distances from the spray centerline. Orthogonal imaging of the scattering light sheets reveal internal spray structure not previously observed using the ballistic imaging method. Sheet scattering further revealed that an intact liquid core is not observed at the injection pressures investigated. Images indicate a droplet-laden flow with significant shear-driven vortical structures, highly transient spray breakup, and significant internal spray structure.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jun 25, 2021
- Source ID
- W911NF1210166
Entities
People
- Terence Parker
Organizations
- Army Contracting Command
- Colorado School of Mines
- United States Army