Effects of humidified enriched air on combustion and emissions of a diesel engine

The potential of Humidified Enriched Air (HEA) on Diesel engine combustion is investigated, by means of 3D CFD combustion simulations, on a current production 4-cylinder turbocharged Diesel engine. HEA is supposed to be obtained by water degassing operation, exploiting the different vapor-liquid equilibria of it main constituents, nitrogen and oxygen. Simulations are carried out using a customized version of the KIVA 3V code, featuring a detailed chemistry combustion mechanism. The model of the engine is previously validated through comparison with experimental data and then it is used to analyse combustion and emissions of HEA combustion in combination with late injection strategies. Numerical results demonstrate that oxygen-enriched air enhances the thermal efficiency of the engine (up to 13%) and reduces significantly soot emissions; on the other hand, in-cylinder peak pressure and NOx emissions increase. The latter can be significantly reduced by using humidified air maintaining the advantage in terms of thermal efficiency and in soot reduction, nevertheless the baseline case NOx emissions cannot be restored.