Reduction of NOx emissions by numerical optimization of the injection timing for a diesel naval engine

The influence of timing injection on NOx emissions is well known in the literature. If for new engines the requirements imposed by Annex 6 of MARPOL (the document limiting pollutant emissions to ships) are easy to meet, the problem of reducing NOx emissions for in-service engines is a difficult one. The only practical solutions in this situation are to change the injection advance and the injector opening pressure. Practically this is done on the test bench by making adjustments and measurements. This paper aims to analyze this problem using a simulation software developed by the author. The software used simulates the engine cycle without gas exchange processes with the aid of a multidimensional 2.5 D model, completed with phenomenological models for injection modeling. NOx emissions are calculated using a system of 10 equations based on the extended Zeldovich mechanism of which 4 are kinetic and 6 at equilibrium. Complex numerical simulations are presented for the most important operating modes of the chosen engine, performed for different injection timing. The results obtained are compared at the end with the experimental measurements performed on the test bench in order to evaluate the accuracy of the simulations performed and the practical utility of the results obtained to achieve the proposed objective.