Effects of fuel injection strategies on combustion and emissions of intelligent charge compression ignition (ICCI) mode fueled with methanol and biodiesel

摘要

In this paper, the prospective experiment of methanol-biodiesel dual fuel in intelligent charge compression ignition (ICCI) mode was conducted to study the effects of fuel injection strategies on engine combustion and emissions. Methanol and biodiesel were successively directly injected into a modified compression ignition (CI) engine to realize flexible and independent stratifications of concentration and reactivity of the in-cylinder mixture. In ICCI experiments, indicated thermal efficiency (ITE) reaching to 53.5% and NOx emissions well below 0.6 g/kWh were obtained, accompanied with acceptable CO and HC emissions under the medium-to-high loads. The stable combustion was achieved by collaborative optimizations in injection timings and energy ratios of methanol-biodiesel dual fuel, which reflected in the proper maximum pressure rising rate and combustion phase. The effects of methanol and biodiesel injection timings on ICCI combustion and emissions presented different tendencies spatially and temporally. Concretely, the earlier combustion phase and increasing combustion rate were mainly attributed to the slight postponement of biodiesel injection timing, while the distribution uniformity and mixing sufficiency of the charged mixture were primarily improved by the advanced injection of methanol. In addition, two-stage split-injection strategy for methanol was conducive to reducing HC and CO emissions along with extremely low NOx emissions, and that for biodiesel contributed to promoting the indicated thermal efficiency and reducing the nucleation particles.