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The transition from HCCI to PPC: Investigation of different injection timing on ignition and combustion characteristics in an optical PPC engine
ISSN: 0148-7191, e-ISSN: 2688-3627
To be published on April 14, 2020 by SAE International in United States
The partially premixed combustion (PPC) concept is regarded as an intermediate process between the fully mixed Homogeneous charge compression ignition (HCCI) combustion and compression ignition (CI) combustion. It is also a combination of auto-ignition mode, a fuel-rich premixed mode, and a diffusion combustion mode. To achieve high efficiency and low soot emission, the in-cylinder mixture process and combustion behavior of PPC are still to be further explored using laser diagnostic. In this paper, combined combustion deriving from three stages (HCCI stage, transition stage, PPC stage) was achieved by using double injection strategies changing from -220° to -8° after top dead centre (ATDC) in an optical heavy-duty CI engine. To analyze how the double injection effect the transition performance from HCCI to CI, spray development was recorded by Mie-scatter and natural luminosity of combustion was captured by a high-speed camera. The result shows double injection reshapes the transition trend of gross efficiency, ignition location, and combustion propagation compares to single injection. The cases in PPC region has the highest gross efficiency. With fuel injected into piston bowl, the ignition location is shifted from centre of the piston to piston bowl. As more fuel is injected in PPC region, the luminosity intensity is mainly located at the piston bowl region instead of homogeneous distribution in the whole chamber.