Research on effects of early intake valve closure (EIVC) miller cycle on combustion and emissions of marine diesel engines at medium and low loads

The Miller cycle with EIVC is applied to a medium-speed marine diesel engine to achieve high-efficiency combustion and low nitrogen oxide (NOx) emissions. The effects of Miller cycle on the state parameters, combustion characteristics, NO emissions, and the spatial distribution of working fluid were analyzed. A one-dimensional (1D) simulation model was established by using the BOOST software. The FIRE software was used to simulate the combustion process and emission characteristics of the diesel engine at medium and low loads. The results show that in the E3 cycle (four kinds of loads, 100%, 75%, 50%, 25%, according to Marine application propeller law), with the proper EIVC, the in-cylinder pressure, temperature and NO emission will be reduced. At the load of 50%, NO emissions were reduced by 17.8%, At 25% load NO emissions were reduced by 14.9%. During the fuel injection, the decrease of in-cylinder temperature causes a longer ignition delay period. When the EIVC is too early, the heat release rate increases sharply, at the same time, the NO generation also increases. Furthermore, it will lead to misfire at low load.