Current trends on combustion control methods using fuel reactivities

Compression ignition (CI) engines are used in heavy duty engine applications due to their high torque capability and thermal efficiency. However, high NOx and smoke emissions are the challenges in using CI engines. Homogeneous charge compression ignition (HCCI) is one of the best methods to reduce NOx and smoke emissions. However, controlling the combustion for an entire range of operation in HCCI mode is a challenging task. Different methods like fast thermal management (FTM), exhaust gas recirculation (EGR), turbo charging and reactivity controlled compression ignition (RCCI) are reviewed and discussed in this article. RCCI is similar to HCCI, which uses reactivities of two different fuels to control combustion. The combustion objectives of HCCI such as less NOx and soot emission can also be obtained through this method. Combustion control based on reactivities of various fuels (RCCI) is discussed significantly. Fuels that have different reactivities can help to control the combustion phasing and thereby reducing the emission. Two different fuels can be injected together into the manifold or one fuel can be injected in the port and other in the combustion chamber directly for reactivity based combustion control. The technological development in different combustion control methods is reviewed and discussed in this article which is a useful knowledge base for further research investigations. When compared to other combustion control methods, RCCI is found to be advantageous in all perspectives such as cost, flexibility in control, simplicity and wide range of operation.