Paradigm shift from mechanical direct injection diesel engines to advanced injection strategies of diesel homogeneous charge compression ignition (HCCI) engines- A comprehensive review

The demand for higher fuel economy and lower exhaust gas emissions of compression ignition (CI) engine cannot be achieved by just using mechanically governed fuel injection systems. The electronically operated fuel injection system is the heart of a CI engine and has become one of the essential technologies to control critical in the recent years. High computing power of microcontrollers has made it possible for controlling injection of fuel electronically at any injection pressure (IP), any crank angle (CA) and for any duration during the engine operation. The common rail direct injection (CRDI) system improves the brake thermal efficiency (BTE) of CI engine with simultaneous reduction in emission levels. A newer concept of homogeneous charge compression ignition (HCCI) operation using CRDI, further reduces the particulate matter (PM) and NOx emission to almost zero level with slightly lower BTE. Such engines however have higher hydrocarbon (HC) and carbon monoxide (CO) emissions in the engine exhaust gas. Hence, there is a need to discuss the performance, emission and combustion of CI, CRDI and HCCI engine operation fuelled with alternative fuels and this paper presents an exhaustive review on these aspects.