Improvement of Center Injection Spray Guided DISI Performance

Spray guided DISI, a next-generation DISI system, is now under development as a gasoline engine which will contribute to improving fuel consumption. The authors have carried out a study to improve fuel consumption and exhaust emissions resulting from a spray guided DISI system with a center injection structure, which is being developed as a system with superior combustion stability.

The primary issue for the center injection structure is to reduce changes in the fuel spray characteristics resulting from carbon deposits near the injector nozzle holes. The secondary issue for this structure is to improve the mixture formation.

To address these two issues, the authors have studied the following measures, which have been shown to maintain stable combustion conditions, as well as offer some improvement to fuel consumption and exhaust emissions performance.

1. (1)
   Combustion gas sealing at injector tip
   Reducing the amount of heat received to the injector tip was successful in lowering the surface temperature and in reducing the formation and accumulation of carbon deposits. This subsequently reduced the changes which occurred in the spray shape and fuel flow rate over time, allowing continuous stable combustion.
2. (2)
   High pressure fuel injection and external EGR
   Improved spray atomization due to high pressure fuel injection resulted in the suitable stratified mixture for combustion with the center injection structure, and thus improved fuel consumption and reduced HC emissions. The increase in NOx emissions, which resulted from the more active combustion was eliminated by external EGR.