Premixed compression ignition (PCI) combustion was implemented using advanced injection strategy and exhaust gas recirculation in a direct-injection single-cylinder diesel engine. The injection timing swept experiment using a baseline injector, which had an injection angle of 146° and 8 nozzle holes, obtained three types of combustion regime: conventional diesel combustion for an injection timing of 10° CA (crank angle) BTDC (before top dead center), PCI combustion for an injection timing of 40° CA BTDC and homogeneous charge compression ignition (HCCI) combustion for an injection timing of 80° CA BTDC. PCI combustion can be verified by burn duration analysis. The burn duration, which was defined as the period from 10% to 90% of the accumulated heat release, was very short in PCI combustion but not in the others. PCI combustion with an injection timing of 40° CA BTDC was achieved in a range of an exhaust gas recirculation (EGR) rate from 0% to around 40%.
Two types of different injectors were applied to investigate the effect of injection angle and the number of nozzle holes on PCI combustion: one had an injection angle of 70° and 8 nozzle holes, the other had an injection angle of 70mD and 14 nozzle holes. These two injectors could implement PCI combustion as well. The indicated mean effective pressure (IMEP) for both injectors with a narrow injection angle (70°) was higher than that for the baseline injector because the injected fuel could be directed toward the piston bowl so that most of the fuel could participate in the combustion. The IMEP for the injector with 8 nozzle holes was higher than that for the injector with 14 nozzle holes. On the other hand, when the injection angle was 70°, the injector with 14 nozzle holes had low levels of HC and CO emissions because of better air utilization compared with the injector with 8 nozzle holes, which was supported by a spray cone angle analysis. A maximum pressure rise rate (MPRR) analysis showed that the MPRR for PCI combustion was higher than that for conventional diesel combustion and HCCI combustion. The MPRR for the injectors of a narrow injection angle in PCI combustion was higher than that for a baseline injector. However, for the injectors of a narrow injection angle, there was no difference in the MPRR of PCI combustion with respect to the number of nozzle holes.