Modeling Diesel Spray, Combustion and Emission with GTEA Numerical Code 2019-01-0004

A detailed chemistry-based CFD model (GTEA, General Transport Equation Analysis) is developed to simulate the diesel spray, combustion and emission process. The numerical model incorporates an improved droplet tracking model, the Hybrid breakup model that consider the influence of turbulence inside the nozzle, the reaction mechanism of n-decane coupled with a reduced NOx mechanism, a phenomenological soot model, a modified dynamic mesh model, a spray/wall impingement model, and other improved sub models in the GTEA codes. The model is first applied to predict the diesel spray process. The computational results demonstrate that the model is capable of predicting satisfactory fuel spray process, and the improved agreement is attributed to the ability of the new Hybrid breakup model to account for the effects of turbulence inside the nozzle, which enhance the spray process. The model is also applied to investigate the ignition delay and flame lift-off length under different ambient conditions. The overall trend of ignition delay and lift-off length with the variation in different conditions is well reproduced by the model. It is found that the ignition delay and lift-off length are a function of ambient density, ambient temperature and oxygen concentration, respectively. This part of study also showed that the longest ignition delay time has the longest lift-off length. Finally, the model is employed to simulate the combustion and emission characteristics of a low-temperature combustion (LTC) engine. Good levels of agreement in cylinder pressures under different EGR conditions are obtained. Predictions of soot and NOx emission are also performed. Although the predicted results are not fully satisfactory, the general trends are still well captured by the simulation.