Abstract
This study aims at finding the favorable combination of combustion-chamber shape and injection parameters when using two-stage injection. The experiments were carried out with various injection conditions, such as spray angle and injection timings and fuel-quantity ratio of two-stage injection, using three types of combustion chamber at low and middle loads. The results show that the strong flow in reentrant-type combustion chamber makes over-lean mixture from first-stage injection at a low load leading to an increase in unburned species emissions, while smoke emission is markedly reduced at a middle load. Increasing first-injection quantity reduces unburned species emissions at a low load but increases NOx emissions. The larger bowl diameter is effective to reduce unburned species emission for later first-stage injection at a low load; however, it causes an increase in smoke emission at a middle load.
