Experimental study on combustion and emissions of n-butanol/biodiesel under both blended fuel mode and dual fuel RCCI mode

Oxygenated biofuels have become one of the research focuses of engines due to their renewability and improvement in combustion. There has been some studies concentrating on the dual fuel RCCI mode or blended combustion mode using biofuels in engines and valuable progress has been obtained. However, the comparison between biofuel RCCI and blended combustion modes has been rarely reported. Therefore, in current work, experimental study was conducted on a single-cylinder engine to investigate the differences between the two combustion modes fueled with biodiesel/n-butanol at different EGR rates (0%, 30%, 50%), n-butanol ratios (20%, 50%, 80%), injection timings and engine loads (low, medium, high). Results show that the ignition delay of blended mode is longer than that of RCCI mode, and more sensitive to n-butanol ratio and EGR rate. The optimum EGR rate is 30% considering efficiency and emissions for both combustion modes. Blended fuel mode can maintain high efficiency at all test loads and n-butanol ratios, the maximum indicated thermal efficiency (ITE) is up to 47.5%, while RCCI only shows comparable efficiency at high load. The problem of high maximum pressure rise rate (MPRR) that blended fuel mode faces can be addressed by retarded combustion phasing. Under current research conditions, blended fuel mode usually presents lower soot, HC, CO emissions and slight higher NOx compared with RCCI mode. Generally, blended mode has better performance when MPRR problem is addressed while RCCI mode shows the potential in load extension due to the low MPRR and flexible split ratio and injection timing.