Combustion and emission analysis of the direct DME injection enabled and controlled auto-ignition gasoline combustion engine operation

Controlled auto-ignition (CAI), also known as HCCI combustion has been researched extensively for gasoline engines due to their potential benefits of improved engine efficiency and low NOx emissions. One of the major challenges of typical CAI/HCCI combustion is to control the start and speed of combustion. In order to introduce some control over the heat release process of a premixed gasoline and air mixture, direct DME injection was exploited to enhance the mixture ignitability and control the combustion timing of the combustible mixture. The heat release rate and ignitability were also regulated by the internal exhaust gas recirculation (EGR). In this research, this was achieved and tested in a single cylinder gasoline port fuel injection engine by the use of Positive Valve Overlap (PVO) and direct DME injection via a commercial Gasoline Direct Injection (GDI) injector. Three DME injection strategies, early single injection, split injection and late single injection, were applied to implement pure auto-ignition, hybrid combustion of flame assisted auto-ignition, and flame propagation, respectively, as the engine load increases. Stable combustion was achieved from 1.3 bar net IMEP to 9.1 bar net IMEP with 90% reduction in NOx emission than the SI combustion operation.