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Over the past few decades, Homogeneous Charge Compression Ignition (HCCI) or Controlled Auto-Ignition (CAI) if it is fuelled with gasoline type of fuels has shown its potential to overcome the limitations and environmental issue concerns of the Spark Ignition (SI) and Compression Ignition (CI) engines. However, controlling the ignition timing of a CAI engine over a wide range of speeds and loads is challenging. Combustion in CAI is affected by a number of factors; the local temperature, the local composition of the air/fuel mixture, time and to a lesser degree the pressure. The in-cylinder engine charge flow fields have significant influences on these factors, especially the local gas properties, which leads to the influences towards the CAI combustion. In this study, such influences were investigated using a Computational Fluid Dynamics (CFD) engine simulation package fitted with a real optical research engine geometry.

Engines with controlled auto-ignition (CAI) combustion offer a number of benefits over conventional spark ignited (SI) and compression ignited (CI) engines, such as much lower NOx emission due to its relatively low combustion temperature, negligible cycle-to-cycle variation due to its self-ignition nature, higher combustion efficiency at part load than its SI counterpart, and low soot emissions since a homogeneous lean air/fuel mixture is being employed. Unlike conventional SI and CI engines, where combustion is directly controlled by the engine management system, the combustion in CAI engines is controlled by chemical kinetics only. Over the past two decades, a number of technologies have been developed to initiate such combustion on both 2 and 4-stroke engines with various fuels, but none of them could maintain the combustion over the wide engine operation range. Remaining problems include control of ignition timing and the heat release rate over the entire engine operation range.