Due to the increasing awareness of environmental protection, limitations on exhaust emissions of diesel engines have become increasingly stringent. This challenges diesel engine manufacturers to find a new balance between engine performance and emissions. Advanced combustion modes for diesel engines, such as homogeneous charge compression ignition (HCCI) and premixed charge compression ignition (PCCI), which can simultaneously reduce exhaust emissions and substantially improve thermal efficiency, have drawn increasing attention. In order to allow enough time to prepare the homogeneous mixture, the early injection strategy has been utilized widely in HCCI and PCCI diesel engines. This paper is aimed at providing a comprehensive review of the effects of early injection parameters on the performance and emissions of HCCI and PCCI engines fueled by both diesel and alternative fuels. Various early injection parameters, including injection pressure, injection timing, and injection angle, are discussed. In addition, the effect of the blending ratio of alternative fuels is also summarized. Every change in parameters has its own advantages and disadvantages, which are explained in detail in order to help researchers choose the best early injection parameters for HCCI and PCCI engines.

The numerical models for barrel-shaped rings of four textures have been established by using MATLAB and the corresponding specimens have been fabricated by laser surface texturing. The performance is compared both theoretically and experimentally in order to investigate the effects of geometrical characteristics. The results of the theoretical analysis indicated that a micro-dimple texture on both sides of the ring surface was a suitable option for improving the lubricating property due to the “collective’’ effect, so it could have a good result on piston ring friction reduction. This result was confirmed experimentally. The micro-dimple texture at the crowning of the ring face weakened the hydrodynamic pressure effect and increased the friction, as demonstrated by both the theoretical and experimental results.