CFD Evaluation of Effects of Split Injection on Combustion and Emissions in a DI Diesel Engine

Effects of split injection with different EGR rate on combustion process and pollutant emissions in a DI diesel engine have been evaluated with CFD modeling. The model was validated with experimental data achieved from a Caterpillar 3401 DI diesel engine and 3D CFD simulation was carried out from intake valve closing (IVC) to exhaust valve opening (EVO). Totally 12 different injection strategies for which two injection pulses with different fuel amount for each pulse (up to 30% for the second pulse) and different separation between two pulses (up to 30° CA) were evaluated. Results show that adequate injection separation and enough fuel amount of the second pulse could form a separate 2nd stage of heat release which could reduce the peak combustion temperature and improve the oxidation of soot formed in the first heat release stage. This suggests, by optimizing split injection configurations accompanied with appropriate EGR rate, both NOx and soot emissions can be controlled effectively.