Effects of fuel injection parameters on performance and emissions formation in a large-bore marine diesel engine

Reductions in the emissions of nitrogen oxides (NOx) and soot from marine diesel engines can be supported by employing multiple-injection strategies, similar to those used in automotive engines. In the present computational study, the possibility of improving the operation of a large two-stroke marine diesel engine at full load by implementing an appropriate pilot injection is explored. A KIVA-3-based computational fluid dynamics code is used, coupled with an evolutionary algorithm. Multi-objective engine optimization is performed by parameterizing the fuel injection profiles in terms of four design variables, which fully define the pilot and main injections. Two objective functions are defined: the final NOx concentration and the specific fuel oil consumption (SFOC), both normalized by the corresponding values of a reference case of continuous injection. Three problem set-ups have been considered: first, an unconstrained problem; second, a problem constrained by the maximum cylinder pressure; third, a problem constrained by both the maximum pressure and the minimum work output per engine cycle. It is found that, in both the unconstrained and the one-constraint problems, the optimum solutions are characterized by substantial improvements in the NOx emissions (of the order of 15-20 per cent) and the SFOC (of the order of 2 per cent). The improvements are less pronounced when both constraints are imposed. A detailed sensitivity analysis of the effects of each of the design variables is presented. © Authors 2011.