Homogeneous charge compression ignition in lowering soot and other emissions for internal combustion engines

Air pollution and global warming are two challenging issues that scientists and engineers are currently tackling with high priority. Within the automotive industry, these challenges mainly lie in reducing vehicle exhaust emissions and improving fuel and combustion efficiency. In this chapter, problems concerning exhaust emissions of soot, NO_x, CO₂, and unburned hydrocarbons from an internal combustion engine (ICE) are discussed first, including laws and regulations governing emission levels in various countries. Further, analysis is made on the recent shift from increasing mechanical power while maintaining fuel consumption to significantly reducing fuel consumption and emissions while maintaining power. Methods to reduce emissions and to improve performance in conventional engines are also discussed. The chapter then focuses on the latest development in ignition and combustion technology for new engine types. Homogeneous charge compression ignition (HCCI) which combines the concepts and advantages of petrol and diesel engines is discussed in detail. The combustion temperature of HCCI is about 500K below conventional diesel and spark ignition engines. As a result, an HCCI engine emits near zero levels of soot or particulate matter and achieves about 90-98% reduction in NO_x raw emissions.