Marine dual fuel engine modelling and parametric investigation of engine settings effect on performance-emissions trade-offs

The continuous stringent requirements of the environmental regulations along with the LNG fuel penetration and the development of port and bunkering facilities, render the use of the dual fuel engines an attractive alternative
of the traditional ship propulsion plants based on Diesel engines running with HFO for reducing both the plant operating cost and environmental footprint. The present study deals with the computational investigation of a
large marine dual fuel (DF) engine of the four-stroke type for comparing its performance and emissions, in both diesel and gas mode operation by using the commercial software GT-ISE. The engine diesel model was initially
set up and calibrated to adequately represent the engine operation. Subsequently, the engine dual fuel model was further developed by considering the injection of two different fuels; methane in the cylinder inlet ports and pilot diesel fuel into the engine cylinders. The derived results were analysed for revealing the differences of the engine performance and emissions at each operating mode. In addition, the turbocharger matching was investigated and discussed to enlighten the turbocharging system challenges due to the completely different air−fuel ratio requirements in diesel and gas modes, respectively. Finally, parametric simulations were performed for gas
mode operation at different loads by varying pilot fuel injection timing, inlet valve closing and inlet manifold boost pressure, aiming to identify the engine settings that simultaneously reduce CO2 and NOx emissions considering
the air−fuel ratio operation window limitations. The parametric study results are discussed to infer the engine optimal settings.