Effects of Spray Characteristics with Different Geometries on the Performance of a DI Diesel Engine 2008-01-2468

The characteristics of diesel spray injected into the cylinder provide crucial clues to the perception of the combustion performance in a compression ignition engine. In this study, five different diesel common rail injectors were examined which have different hole numbers, orifice sizes, jet cone angles, and hydraulic flow rates. Both the macroscopic and microscopic characteristics of diesel sprays were compared through Mie-scattered light imaging and PDA (Phase-Doppler anemometry) measurements. Seven hole injector with smaller hole was found to give better air/fuel mixing and favorable droplet size compared with other injectors.

To evaluate the feasibility of achieving lower emission level with the different diesel sprays, the combustion and emission characteristics in case of 6 and 7 hole injectors were investigated under the same fuel flow rate condition in a light duty DI diesel engine. The results showed that 7 hole injector with pilot injection had shorter combustion delay and combustion duration, but these effects were not found in high speed and high load condition with no pilot injection. The seven hole injector could be utilized to achieve lower emission compared with six hole one because of more improved spatial distribution of fuel in combustion chamber. The full load performance such as brake torque and thermal efficiency of 6 and 7 hole injectors were slightly different according to the engine speed.