INVESTIGATION OF THE MILLER CYCLE ON THE PERFORMANCE AND EMISSION IN A NATURAL GAS-DIESEL DUAL-FUEL MARINE ENGINE BY USING TWO ZONE COMBUSTION MODEL

Compared to the standard cycle, the Miller cycle decreases the cylinder maxi-mum combustion temperature which can effectively reduce NOx emissions. In this paper, a 0-D two-zone combustion model is used to establish the simulation mod-el of a marine dual-fuel engine, which is calibrated according to the test report under different loads. Due to the high emissions under part load, the Miller cycle (early intake valve closing method) is used for optimization. By analyzing the cyl-inder pressure, temperature, heat release rate, and NOx emissions under different cases, it can be found that the effective working volume and thermal efficiency decrease with the advance of intake valve closing and improve with the increase of the geometric compression ratio. In all optimization cases, the NOx emissions and fuel consumption are reduced by 72% and 0.1%, respectively, by increasing the geometric compression ratio to 14 and the intake valve closing timing to 510 °CA (the reference top dead center is 360 °CA). The simulation results show that the early intake valve closing Miller cycle can effectively reduce the NOx emis-sions and cylinder peak pressure.