Effect of bioethanol on combustion and emissions in advanced CI engines: HCCI, PPC and GCI mode - A review

This review mainly concerns the use of bioethanol in advanced compression ignition (CI) engines. Various advanced CI engines are in existence, and this review discusses, homogeneous charge compression ignition (HCCI) combustion, partially premixed combustion (PPC) and gasoline compression ignition (GCI) combustion for discussion. Four different experimental configurations were adopted to measure the autoignition or ignition delay time for ethanol in HCCI combustion mode. The mixture formation strategies in bioethanol HCCI combustion can be categorized into three groups: external, internal and combined mixture preparations. The external mixture preparation is subdivided into port fuel injection and a vaporizer, and the internal mixture preparation into early, late and multiple direct injections. A numerical simulation for ethanol HCCI combustion was recently carried out with a direct numerical simulation and large eddy simulation. The different reduced chemical kinetic mechanisms for ethanol oxidation models present in the literature are summarized in detail. Detailed mechanisms including 57 species and 383 reactions were employed in numerical simulations of ethanol HCCI combustion. The pressure rise rate, ringing intensity and noise meter calculation for the knock limit and coefficient of variation of indicated mean effective pressure for misfire limit were used. The pressure rise rate has been extensively adopted for the upper limit of the HCCI and PPC combustion, and the acceptable limit for the maximum pressure rise rate is found to be subjective. Studies related to PPC and GCI modes fueled with ethanol makes use of fueling configuration that are divided into single and double injections. A double injection strategy was preferred for ethanol PPC with a combination of 50% EGR and relative equivalence ratio of 0.67. The review of the literature on ethanol PPC and ECI provides an overview of the fueling configuration. Further studies on GCI combustion with ethanol, i.e. ethanol-fueled compression ignition (ECI) are required in the future. In all advanced combustion modes, NOx and soot emissions are low compared to those of conventional diesel engines, and HC and CO emissions are still high in all advanced combustion concepts.