Effect of n-butanol/diesel blends and piston bowl geometry on combustion and emission characteristics of CI engine.

The present study describes the experimental and numerical analysis of the combustion and emission characteristics of CI engine operated with diesel-butanol blends. Experiments were carried with neat diesel fuel (i.e., Bu00) and its blends of n-butanol, 10%, 20% and 30% by volume (Bu10, Bu20 and Bu30) at a constant speed and rated load. From the experimental results, it is observed that CO, NOx and smoke emissions decreased, whereas the unburned hydrocarbon (UBHC) emission increased with increasing butanol content, as compared to Bu00. From the experimental analysis, it is also observed that Bu20 blend gives higher brake thermal efficiency (BTE) and lower brake specific energy consumption (BSEC) as compared to Bu00, Bu10 and Bu30, but produces higher UBHC. In order to decrease the UBHC emission, different piston bowl geometries were analysed using simulation studies. The combustion and emission characteristics of the CI engine operating with Bu20 blend for three different piston bowl geometries viz., hemispherical combustion chamber (HCC), shallow combustion chamber (SCC) and toroidal combustion chamber (TCC), were studied using CONVERGE CFD code. The simulation model was validated with experimental results of the baseline engine configuration (HCC) for diesel fuel as well as Bu20 blend. The results showed that there is a significant reduction in UBHC and improvement of performance for SCC and TCC piston geometry compared to HCC piston geometry. However, a slight increment of NOx emissions was observed.