The application of low-carbon fuels represents a critical pathway for decarbonizing marine engines, with methanol-diesel high-pressure dual direct injection (HPDI) technology emerging as the most viable solution for current methanol dual-fuel marine engine systems. However, injection quantity fluctuations can lead to significant deterioration in engine performance and emissions. To address this challenge, this study developed a methanol-diesel HPDI system simulation model to investigate the mechanism of fuel injection fluctuations. The research demonstrates that excessive pressure differentials between methanol and diesel injection induce characteristic fuel pressure fluctuations that critically affect needle valve motion and injection rate profiles, resulting in pronounced cycle-to-cycle variations in methanol injection characteristics. Under conditions of narrow methanol injection pulse widths, insufficient time for full needle valve opening causes the valve to remain in a floating state during the injection cycle. The transient pressure fluctuations acting on this floating needle valve introduce substantial inconsistencies in its motion dynamics. The study reveals that rapid needle valve positioning represents a crucial strategy for reducing HPDI system injection variability. A radial basis function neural network-based predictive model is constructed to forecast needle valve movement states, coupled with a multi-objective Grey Wolf Optimizer approach to enhance needle valve motion consistency. The optimization results demonstrate maximum reductions of 50.3% in methanol injection fluctuation rate δQ, with post-optimization δQ values consistently maintained below 5% across all operating conditions, thereby significantly improving HPDI system injection consistency.
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