Real time model for oxides of nitrogen emissions from a slow speed marine diesel

Abstract

A thermodynamic model is presented for predicting oxides of nitrogen (NOx) emissions from slow speed marine diesel engines. The model is zero-dimensional, uses chemical kinetics for NOx formation in multiple burnt gas zones, and runs in real time on a standard PC. The mean fuel/air mixture strength at which NOx forms and the rate of dilution of the burnt gas by unburnt air, are adjustable. Two MAN B&W IMO NOx-compliant slow speed diesels are modelled. Effects such as variations in fuel spray interaction with load are accounted for in the calibration of the model. The effect of dilution rate and equivalence ratio on NOx formation is studied. It is shown that, under certain conditions, there is a critical burnt gas dilution rate which maximises NOx. The model responds adequately to changes in engine load and to NOx control measures such as water injection, injection timing retard, exhaust gas recirculation and humidification.