Bio-diesel in homogeneous charge compression ignition (HCCI) combustion

The continuously growing energy demands and the fast depleting fossil fuels reserves has led the research towards seeking alternative fuels and combustion concepts to combat the challenges. Biodiesel is one of the potential alternative fuels due to its being renewable in nature. Use of biodiesel in CI engines is generally found to reduce emissions of hydrocarbons (HC), carbon monoxide (CO), and particulate matters (PM); but to increase emission of oxides of nitrogen (NOx) as compared to conventional diesel fuel. Homogeneous charge compression ignition (HCCI) combustion, an advanced combustion concept for internal combustion (IC) engines, is believed to be a promising one due to its high efficiency and lower NOx and PM emissions. However, some issues such as difficulty in combustion phasing control, high levels of UHC and CO emissions, limited range of operation, cold starting problem, difficulty in homogeneous mixture preparation, abnormal pressure rise with noise, lacking in prompt response during cycle transient, engine control strategies and systems, cylinder to cylinder variation and the lack of accurate chemical mechanism and precise combustion model need to be resolved for successful operation of HCCI engine. The characteristic feature of HCCI combustion is the requirement of preparing a homogenous mixture before the start of combustion. In HCCI combustion, the entire combustion process lacks a direct method for the control of ignition timing and combustion rate, which are rather controlled primarily by chemical kinetics, and to a lesser degree, by turbulence and mixing. Biodiesel and its blends with diesel, if coupled properly with HCCI combustion concept, has the potential to reduce the exhaust emissions substantially, while maintaining the performance standards close to the conventional compression ignition (CI) engines. This paper reviews the concepts and methods of HCCI combustion and provides an overview of use of biodiesel in conventional compression ignition direct injection (CIDI) and HCCI engine. (C) 2015 Elsevier Ltd. All rights reserved.