Multiple Optical Diagnostics on both Partially Premixed Combustion (PPC) and Reactivity Controlled Compression Ignition (RCCI)

摘要

The mixing and combustion process of partially premixed combustion (PPC) and reactivity controlled compression ignition (RCCI) was investigated on a light-duty optical engine. In PPC mode, PRF70, a mixture of 70% iso-octane and 30% n-heptane by volume, was directly injected into the cylinder. In RCCI mode, 70% iso-octane was supplied by the port fuel injector and 30% n-heptane was directly injected. The overall fuel reactivity is the same to PPC and RCCI and the overall fuel/air equivalence ratio was kept at 0.77 for both combustion modes. The direct-injection timing was set to -25°C A ATDC. The results found that the local fuel-rich regions were formed before high temperature heat release (HTHR) and the maximum fuel/air equivalence ratio was lower than 1.2 for PPC and was lower than 1.6 for RCCI. The PRF number covered 35-80 before HTHR for RCCI, while the PRF number was always 70 for PPC. Distinct flame front propagation for PPC was seen during the early stages of the flame development process by the high-speed images, formaldehyde and OH planar laser-induced fluorescence (PLIF) imaging. However, for RCCI, there was no distinct flame front propagation based on high-speed images, formaldehyde and OH PLIF, and RCCI was a staged multi-sites auto-ignition combustion process.