Experimental study of the bioethanol substitution rate and the diesel injection strategies on combustion and emission characteristics of dual-fuel-direct-injection (DFDI) engine

Bioethanol is receiving broad attention as an alternative fuel due to environmental and energy scarcity issues. It is determined that the oxygenated groups and strong evaporation of bioethanol applied to diesel engines could potentially reduce NO_x and soot by reducing the combustion temperature and incomplete combustion. In this paper, an experimental study on the effect of bioethanol substitution rate (ESR) and different diesel injection strategies on the engine performance, combustion, and emission in a dual-fuel-direct-injection (DFDI) engine was investigated. In the DFDI mode, bioethanol and diesel were used as low and high reactivity fuels (LRF&HRF), respectively, both of which were injected directly into the cylinder by two independent common-rail systems. It could avoid some drawbacks of port injection. The effects of ESR, diesel injection timing (D_inj), and diesel split injection timing (S_inj) on the engine performances were investigated with a constant heating value of the fuel. Results showed that a moderate ESR in DFDI mode could lead to higher brake thermal efficiency (BTE) and lower NO_x and soot emissions compared to the pure diesel mode. Early injection of diesel resulted in higher BTE, lower CO, THC, and soot, accompanied by higher NO_x. In the split injection strategy, when retarding the first and advancing the second diesel injection timing, as suggested, the BTE increased, and the CO, HC, and soot decreased, followed by NO_x increment. In summary, it is expected that the DFDI mode could achieve high-efficient combustion and acceptable emission requirements.