Experimental study on the influence of low-temperature combustion (LTC) mode and fuel properties on cyclic variations in a compression-ignition engine

In this study, the characteristics of the cyclic variations of three different low-temperature combustion modes including reactivity-controlled compression ignition (RCCI), homogeneous charge compression ignition (HCCI), and partially premixed combustion (PPC) were experimentally investigated at low-to-medium load in a compression-ignition engine. First, the impact of fuel properties on the cyclic variations of RCCI was discussed by utilizing polyoxymethylene dimethyl ethers (PODEs) (P100), diesel/PODEs blend with 30% PODEs by volume (P30), and diesel (P0) as the direct-injection high-reactivity fuel, while gasoline (G) with the research octane number of 98 as the premixed low-reactivity fuel. The results indicated that PODEs could effectively reduce the cyclic variations of RCCI compared to diesel. By varying the premixed ratio and the start of injection timing in the cylinder, it was found that the sensitivity of the cyclic variations of G/P100 RCCI to premixed ratio was lower than that of G/P0 RCCI. In G/P0 RCCI, the cyclic variations of indicated mean effective pressure with premixed ratio of 70% were significantly higher than that with premixed ratio of 90%, and the cyclic variations of CA50 (crank angle of 50% accumulative heat release) considerably reduced with earlier start of injection timing from 40 to 60 degrees CA BTDC. Then, by comparing the cyclic variations of G/P100 RCCI, gasoline HCCI, and gasoline PPC at the same CA50 and the indicated mean effective pressure around 4.5 bar, it was found that the cyclic variations of CA50 of HCCI were much lower than that of RCCI, but they were higher than that of PPC.