Modeling Soot Size Distribution Evolution and Pollutant Formation Inside Diesel Engine Using a 0D Multi-zone Gas Parcel Model with Detailed Chemistry and Soot Microphysics

Diesel engine emits soot which causes harm to human health, air quality and climate. It is important to understand the formation and time evolution of soot and its size distribution evolution inside engines to design strategies for emission reduction. We have developed a 0D multi-zone model for diesel fuel spray and coupled it with detailed surrogate diesel fuel chemistry and a sectional aerosol dynamics model for soot nucleation, surface growth and coagulation. Variable equivalence ratios in different zones are created by fixed fuel injection rates and variable air entrainment rates by a normal distribution function in different zones which ensures the existences of different pollutant forming zones having different equivalence ratios. Engine exit measured data of total soot mass and NOx for one operating condition are used to optimize the three model parameters. Model simulation of soot size distribution is consistent with typical measured data. Other than soot, the model also calculates the concentration of a wide range of combustion products (NOx, CO, SO₂, SO₃, NO, NO₂, N₂O, OH, HO₂ etc.) which may help to study engine exhaust chemistry of pollutant reduction. Sulfur oxidation efficiency ([SO₃]+[H₂SO₄])/([Total S]) is found to be 2% at end of the expansion stroke. The model simulation produces the typical trend that late injection increase soot but decrease NOx. The model may enable us to test the predicting capability of any existing or newly developed chemical kinetic mechanism of surrogate fuel oxidation and soot formation inside the engine.