Performance and Exhaust Emissions Analysis of a Diesel Engine Using Oxygen-Enriched Air

Oxygen enriched air (EA) is a well known industrial mixture in which the content of oxygen is higher respect the atmospheric one, in the range 22-35%. Oxygen EA can be obtained by desorption from water, taking advantage of the higher oxygen solubility in water compared to the nitrogen one, since the Henry constants of this two gases are different. The production of EA by this new approach was already studied by experimental runs and theoretical considerations. New results using salt water are reported. EA promoted combustion is considered as one of the most interesting technologies to improve the performance in diesel engines and to simultaneously control and reduce pollution. This paper explores, by means of 3-dimensional computational fluid dynamics simulations, the effects of EA on the performance and exhaust emissions of a high-speed direct-injection diesel engine. For the analysis, a customized version of the KIVA 3 V code, including a detailed combustion chemistry approach, coupled with a comprehensive oxidation mechanism as a diesel oil surrogate, is used. A current-production 1.3-liter, four-cylinder engine is selected, and available experimental test data are used for validation of the engine model. Using the validated engine model, the effects of enriched air are investigated, along with the influence of injection strategies, under different operating conditions. It is found that oxygen-enriched combustion reduces soot emissions and improves engine thermal efficiency, but also increases in-cylinder peak pressure and nitrogen oxide (NOx) emissions. By changing the start of injection, it is possible to limit in-cylinder pressure to standard values and so reduce the NOx increment.