The effects of hydrogen addition on engine power and emission in DME premixed charge compression ignition engine

Premixed-charge compression-ignition (PCCI) combustion of dimethyl-ether (DME) with double injection strategy was investigated in a single-cylinder compression-ignition engine. DME main-injection was replaced by hydrogen to reduce carbon dioxide emissions. To study the effect of hydrogen, the injected amount of hydrogen was increased. Engine performance and emission of DME PCCI combustion were compared to those of hydrogen–DME PCCI combustion. In the DME PCCI engine operation, DME was injected directly into the cylinder at −120 crank angle degrees (°CA) after top dead center (aTDC) to simulate homogeneous charge at first, and then DME was injected secondly with varied second injection timing. In this case, DME injection timing in the second stage affected the engine performance and emissions. Delayed combustion phase showed a higher indicated mean effective pressure (IMEP), while it increased NOx emission when DME second injection is retarded. In the hydrogen–DME PCCI, hydrogen was injected at intake port with fixed injection timing. DME injection timing in hydrogen–DME PCCI combustion was also varied from −120 °CA to TDC, as in the DME PCCI engine operation. The total supplied heating value was fixed at 400 J for all cases. DME injection timing determined the start of combustion for the hydrogen–DME PCCI. With increasing the amount of hydrogen, exhaust emissions were reduced. Hydrogen–DME PCCI engine was operated with minimum amount of DME via the hydrogen addition and DME injection timing control. The optimized DME injection timing, −30 °CA aTDC, resulted in a lower exhaust emission-operation, while maintaining a higher IMEP.

► Second injection of DME in DICI engine fueled with H2 and DME.
► Increasing fuel ratio of H2 resulted in improved H2–DME engine efficiency.
► With increasing fuel ratio of H2 engine-out emissions could be reduced.
► Controlling the DME injection timing regulated combustion phasing of H2–DME PCCI.