Experimental Study of Multiple Premixed Compression Ignition Engine Fueled with Heavy Naphtha for High Efficiency and Low Emissions

A study of Multiple Premixed Compression Ignition (MPCI) with heavy naphtha is performed on a light-duty single cylinder diesel engine. The engine is operated at a speed of 1600rpm with the net indicated mean effective pressure (IMEP) from 0.5MPa to 0.9MPa. Commercial diesel is also tested with the single injection for reference. The combustion and emissions characteristics of the heavy naphtha are investigated by sweeping the first (−200 ∼ −20 deg ATDC) and the second injection timing (−5 ∼ 15 deg ATDC) with an injection split ratio of 50/50.
The results show that compared with diesel combustion, the naphtha MPCI can reduce NOx, soot emissions and particle number simultaneously while maintaining or achieving even higher indicated thermal efficiency. A low pressure rise rate can be achieved due to the two-stage combustion character of the MPCI mode but with the penalty of high HC and CO emissions, especially at 0.5MPa IMEP.
Attributed to the “spray- combustion- spray- combustion” process, the emissions can be controlled by adjusting the first and second injection timing, respectively. The CO and HC emissions decrease significantly when retarding the first injection timing, while the second injection has a great effect on NOx and soot emissions. The high thermal efficiency will be maintained, if the CA50 is within 20deg ATDC. Thus, low emissions and high efficiency can be gained simultaneously by optimizing the injection timing.