Cooperative optimization of key parameters for enhancing thermal efficiency without knocking in marine two-stroke natural gas dual-fuel engines

Marine two-stroke low-pressure direct injection natural gas dual-fuel engines feature low compression ratios (CR) to avoid knock, which restricts thermal efficiency improvement. This study optimises CR, pilot injection timing (PIT) and exhaust gas recirculation (EGR) via multi-objective methods to boost efficiency without knock. A validated 1D simulation model was established, followed by single-factor analysis and response surface modelling based on Latin Hypercube Design simulation results. NSGA-II and TOPSIS were then used to derive the optimal scheme. Single-factor results show higher CR cuts brake-specific fuel consumption (BSFC) but causes knock; delayed PIT mitigates knock but worsens BSFC; elevated EGR reduces knock risk with BSFC first dropping then rising and NOx emissions varying consistently with knock induction time integral (KITI). Optimisation finds optimal parameters (CR=14.6, PIT=-8.08 °CA, EGR=40%) reduce BSFC by 8.62% and NOx by 85.8% vs the prototype, with KITI and peak cylinder pressure within safe thresholds.1. HighlightsPerformance optimization of marine two-stroke DF engines considering knock suppressionIncreasing compression ratio reduces BSFC but can lead to knockDelaying pilot fuel injection timing reduces knock risk but increases BSFCAppropriate EGR rates improve both BSFC and knock performance simultaneouslyCooperative optimization cuts BSFC by 8.62% and NOX emissions by 85.8%