Effects of multiple-injection strategies on overall spray behavior, combustion, and emissions reduction characteristics of biodiesel fuel

摘要

This study described the combustion and exhaust emissions characteristics of biodiesel fuel with multiple-injection strategies. Also, this investigation included the free spray characteristics and in-cylinder spray behaviors of the multiple-injection modes. Free spray and in-cylinder spray images were obtained from the spray visualization system. Combustion and exhaust emissions characteristics were analyzed using a single cylinder diesel engine with a displacement volume of 373.33 cm~3 and a compression ratio of 17.8. The exhaust emissions were analyzed using a smoke meter and an exhaust gas analyzer. A scanning mobility particle sizer (SMPS) was utilized to measure the particle number and size distribution of the nano-sized particle matter. It revealed that the injected spray before BTDC 25° developed toward the piston bowl region, and then progressed along the piston wall. When the biodiesel spray was injected at BTDC 25°, the spray targeted the piston lib. In single-injection combustion, the combustion pressure and rate of heat release at an injection timing of BTDC 30° dramatically decreased. These characteristics influenced on the decrease of the indicated mean effective pressure (IMEP) and the increase of soot, HC, and CO emissions because of the incomplete combustion. The multiple-injection modes showed a higher IMEP than the single-injection mode. In addition, the pilot injection strategy represented a higher IMEP than the split injection mode. The analysis of exhaust emissions characteristics of the multiple-injection modes showed that a short injection interval induced a decrease in soot, HC, and CO emissions, while NO_x emission increased. On the other hand, when the multiple-injection modes applied to the diesel engine, particles with large sizes were significantly decreased compared to single-injection combustion.