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Effect of Jet-Jet Angle on Combustion Process of Diesel Spray in an RCEM
ISSN: 0148-7191, e-ISSN: 2688-3627
To be published on September 15, 2020 by SAE International in United States
The effects of jet-jet angle on the combustion process including the lift-off length and the liquid length of diesel spray were investigated in a rapid compression and expansion machine (RCEM). Experiments were carried out using an optical accessible RCEM equipped with an irregular six-hole nozzle having jet-jet angle of 30 degrees and 45 degrees under various injection conditions and various intake oxygen conditions. High-speed OH* chemiluminescence imaging and direct photo imaging with Mie scattering method were used to capture the transient evolution of the spray flame including lift-off length and liquid length. The RCEM operated at 1200 rpm. The injection timing was -4 deg ATDC, and the in-cylinder pressure and temperature were 6 MPa and 780 K at the injection timing, which achieved short ignition delay. The liquid length and lift-off length of the jet-jet angle of 30 degrees were shorter than those of jet-jet angle of 45 degrees under the condition of intake oxygen concentration of 19%. This is because the high temperature burnt gas was entrained more in the near-nozzle region between fuel jets when the jet-jet angle was narrow. The lift-off length and liquid length were not affected by injection pressure in the range from 80 MPa to 120 MPa. The lift-off length of jet-jet angle of 30 degrees in 15% oxygen concentration was also shortened compared to jet-jet angle of 45 degrees, while the liquid length was not influenced by the jet-jet angle significantly. These trends are explained by the entrained gas temperature and the entrainment behavior.