An experimental and computational study for fuel spray fuel system, engine emissions and the correlation between them was carried out for small bore high-speed direct injection (HSDI) diesel engine. The goal of this work is to characterize two different injection systems for a small bore direct injection diesel engine and to connect the spray behavior with measured and modeled engine performance. The characteristics of transient high injection pressure diesel fuel sprays were investigated by sequential high-speed photographic images. Measurements of spray tip penetration length and spray angle were made based on the spray images, and the spray Sauter Mean Diameter (SMD) was calculated by using the light extinction technique. The multi-dimensional (KIVA-3V) code was validated and used to predict the NOx and soot emissions.
Two HSDI fuel injection systems have been constructed for spray visualization experiments: the first one is a hydraulic electronic unit injector system (HEUI) and the other is a common rail (CR) injector system. Experiments were conducted by using different nozzles under different operating conditions to investigate the effects of injection pressure, nozzle hole size, ambient density, and nozzle type on spray characteristics. Four nozzles were used: two valve covered orifice (VCO) type nozzles, with single and dual-guided needle, and two mini-sac nozzles. The mini-sac nozzles had 158 and 165 micron holes while the VCO had 160 and 174 micron hole diameters. To find the relationships between the spray characteristics and combustion emissions, the spray experiments for the dual-guided needle VCO nozzle used the same conditions as for a set of engine tests performed in a different project. All four nozzles were modeled using KIVA-3V code to explore the relationship between spray behavior and engine performance.
Based on the spray structure analysis, the single-guided VCO nozzle produced considerable hole-to-hole variation early in the injection event than the mini-sac nozzles. It was also discovered that the dual-guided VCO nozzle reduced the hole-to-hole variation but it did not vanished completely. The results showed that injection pressure and hole size are the dominant variables influencing the droplet size. KIVA modeling presented that, for these two systems investigated, the HEUI injection rate shape had NOx level lower than the CR injection rate. The modeling also showed at 45% load and 90 MPa injection pressure that decreasing the nozzle size only by less than 10% had a significant effect on the NOx output level.