A study on the spray, combustion and emissions characteristics of biobutanol fuel in a GDI engine system

Abstract

In this dissertation, the effect of biobutanol blending ratio of biobutanol-gasoline blended fuel on spray characteristics, combustion performance and exhaust emission characteristics in a GDI engine was experimentally investigated under various operating conditions such as various injection strategies. The experiments of this study are divided into spray experiments to provide a basis for the analysis of the main combustion experiment with the combustion and exhaust measurement results. Experiments of the spray characteristics of the biobutanol are performed to determine the injection quantity according to the injection duration , injection rate, and atomization characteristics. To investigate the fuel supply characteristics, the injection rate is determined by applying the Bosch method . In order to determine the spray microscopic characteristics of biobutanol fuel, Phase Doppler Particle Analyzer (PDPA) system with light source of Ar-ion laser. The control of fuel injection was maintained using an air compression type high-pressure pump, and was commonly applied to the common rail system capable of high-pressure injection. The investigation was conducted using a four-cylinder gasoline direct injection engine and with the displacement volume of 1.591L.

The performance experiments of GDI type test engine with a compression ratio of 11.0 are controlled using a 75kW eddy current dynamometer system. In this study, the effect of ignition timings on the performance characteristics of test engine were investigated at various injection timings and injection durations with constant operating conditions such as the intake air temperature and coolant temperature. Comparing the combustion characteristics, the engine combustion pressure, heat release rate, and maximum pressure coefficient of variation were measured and analyzed. In addition, the emissions concentration of exhaust gas through the exhaust line was measured by installing an exhaust gas analyzer, and exhaust emissions generated in the combustion process were measured for HC, NOx and CO emissions in real time. The experiment fuels used were blends of gasoline fuel and biobutanol: B20 fuel (80% gasoline and 20% biobutanol by weight), B40 fuel (60% gasoline and 40% biobutanol by weight), B60 fuel (40% gasoline and 60% biobutanol by weight), and B80 fuel (20% gasoline and 80% biobutanol by weight). The results of the experiment were analyzed under the various blending ratio of biobutanol, the injection quantities and injection rates. The results of PDPA experiments showed that normalized droplet diameters indicated the highest droplet distribution at 0.5mm of axial distance, and it was gradually decreased in accordance with the increase of axial distance. As the injection pressure increases, the droplet SMD distribution were decreased. The size of the SMD showed the increasing trends at higher butanol blending ratios. From the results of the combustion experiment, it is confirm that the oxygen component in the biobutanol fuel is influenced on the increase of maximum combustion pressure and the maximum rate of heat release. Furthermore, biobutanol fuel promoted complete combustion, with CO reduced 27% or more compared to gasoline: in addition HC and NOx were reduced 20% or more. The effect of oxygenating components to promote complete combustion is determined to be large.