Parametric investigation on the performance-emissions trade-off and knocking occurrence of dual fuel engines using CFD

Dual fuel (DF) engines have been an attractive alternative of traditional diesel engines for reducing both the environmental impact and operating cost. The major challenge of DF engine design is to deal with the performance-emissions trade-off via operating settings optimisation. This study aims at parametrically investigating the engine settings optimisation for a simultaneous reduction of NOx emissions and brake specific fuel consumption (BSFC) of marine DF engines while avoiding knocking accurrence by using a computational fluid dynamics (CFD) model. The model is developed in the CONVERGE software and validated by employing the measured in-cylinder pressure and emissions. Subsequently, the model is used to parametrically investigate the engine operating settings (pilot injection timing, equivalence ratio and natural gas mass) that allow simultaneous reduction of NOx and BSFC emissions at three engine operating conditions (1800 r/min, 1629 r/min and 1457 r/min). Result shows that the optimal solution at 1800 r/min and 1629 r/min operation conditions can be achieved by controlling the pilot injection timing, equivalence ratio variation and NG mass variation within –5 to –7.5 °CA, –5% to +5% and 0% to +20%, respectively. For the 1457 r/min operation condition, the appropriate ranges of pilot injection timing and the equivalence ratio variation are the same with those at 1800 r/min and 1629 r/min, whilst the NG mass variation range should be between –10% and +10%. The derived results in this study are expected to support the combustion analysis and enhancement of marine DF engines during the design phase, whilst the derived optimal solution is expected to provide guidelines of DF engine management for reducing operating cost and environmental footprint