Premixed compression ignition combustion with various injector configurations in a heavy duty diesel engine

Premixed compression ignition combustion was implemented using early injection timing and exhaust gas recirculation in a direct injection single cylinder diesel engine and was evaluated with respect to the injector configurations. A baseline injector with an injection angle of 146° and eight nozzle holes showed premixed compression ignition combustion at the injection timing of 40° crank angle before top dead centre among three distinct combustion regimes. The burn duration in premixed compression ignition combustion was shortest among the regimes. Premixed compression ignition combustion at an injection timing of 40° crank angle before top dead centre was achieved at an exhaust gas recirculation rate ranging from 0% to approximately 40%. Two different injector configurations were applied to investigate the effect of injection angle and the number of nozzle holes on premixed compression ignition combustion: one had an injection angle of 70° and eight nozzle holes and the other had an injection angle of 70° and 14 nozzle holes. These two injectors could implement premixed compression ignition combustion as well as the baseline injector under the injection timing and exhaust gas recirculation conditions. In case of both injectors with an injection angle of 70°, the indicated mean effective pressures for 8 and 14 nozzle holes increased by 26% and 11%, respectively, because of the increased fuel participating in combustion and the reduced negative work in premixed compression ignition combustion. On the other hand, the injector with an injection angle of 70° and 14 nozzle holes showed the lowest levels of hydrocarbon, carbon monoxide and smoke emissions, which decreased by 82%, 92% and 81%, respectively, in premixed compression ignition combustion. However, the nitrogen oxides emission for the injectors with eight and 14 holes increased by 82% and 68%, respectively, in premixed compression ignition combustion. Natural luminosity from an in-cylinder visualization reveals pool fire of fuel films on the base of the piston bowl when both injectors had a narrow injection angle. For the injector with an injection angle of 70° and eight nozzle holes, a more vigorous pool fire at an exhaust gas recirculation rate of 0% is attributed to a larger amount of fuel film. At an exhaust gas recirculation rate of 40%, however, the portion of unburned fuel films increased the hydrocarbon and carbon monoxide emissions, and the rest of the diffusive pool fire can increase smoke emission surviving under a lack of oxygen. On the other hand, for the injector with an injection angle of 70° and 14 nozzle holes, the hydrocarbon and carbon monoxide emissions were maintained at lower levels due to less formation of fuel film and better air utilization.