Homogeneous charge compression ignition engine: a technical review

The Homogeneous Charge Compression Ignition (HCCI) engine is the combination of both Spark Ignition (SI-Engine or Otto-Engine) and Compression Ignition (Diesel Engine). It uses homogeneous fuel-air mixtures as the SI-engine does and uses typically high compression ratio that allowed mixture to auto-ignite as the diesel engine does. The lean homogenous mixture in HCCI reduces particulate emissions and lean fuel-air mixture helps auto-ignite which is reducing the emission of oxide of nitrogen NOx about 90-98%. It is reported that the HCCI engine offer an increase in fuel efficiency of up to 15-30%, compared with the SI engine. However, HCCI works well only over a relatively narrow operating range, unless engine geometry or operational parameters are adjusted. In HCCI engines combustion is initiated via homogenous charge, and there is no direct in-cylinder mechanism to control auto-ignition. This review paper is focused on HCCI engines performance, challenges, methods to induce combustions, controller design and future direction and trends.