This comprehensive study presents an integrated analysis of NO_x reduction strategies and operational optimization for the HYUNDAI-HiMSEN 7H35DFP dual-fuel marine engine. The optimization scope focuses on selective catalytic reduction control strategies and operational decision-making (fuel mode selection, load management) rather than engine hardware modifications, ensuring practical applicability within certified marine engine operational envelopes. The research employs a multifaceted approach combining experimental investigation, computational fluid dynamics (CFD) modeling, and advanced control algorithms to address the stringent IMO Tier III emission standards. The 3500 kW, 7-cylinder engine achieves IMO Tier III compliance through dual pathways: (1) gas mode operation meeting the 2.4 g/kWh limit inherently with measured emissions of 1.41–2.29 g/kWh across 25–100% load without aftertreatment, and (2) diesel mode achieving compliance via SCR aftertreatment, reducing Tier II baseline emissions (7.68–10.71 g/kWh) by 75–82% to final values of 1.60–1.96 g/kWh. The research quantifies NO_x reduction mechanisms separately for each operating mode and establishes optimal operational strategies for mode selection. A MATLAB v2025a-based SCR optimization model successfully predicts optimal urea injection rates, achieving >75% NO_x reduction efficiency across all operating conditions. Multivariate analysis using principal component analysis identifies the following three primary factors explaining 89.3% of dataset variability: combustion intensity (45.2%), fuel mixing characteristics (28.7%), and thermal management (15.4%). CFD analysis reveals that gas mode combustion produces more uniform temperature distributions (peak ~2000 K) compared to diesel operation (>2200 K), directly explaining NO_x generation differences. The developed digital twin framework with machine learning algorithms achieves 94.2% accuracy in SCR catalyst degradation prediction and 91.8% in fuel injection system performance prediction. Waste heat recovery analysis indicates 25–30% of fuel energy resides in exhaust gases, with theoretical energy recovery potential of 8.5–15.3%. This integrated approach validates dual-fuel technology’s capability to meet current and future maritime environmental regulations while maintaining operational flexibility.

This study experimentally investigated the ignition and combustion characteristics of marine gas oil as a pilot fuel in dual-fuel marine engines using a constant-volume combustion chamber. In-cylinder temperature, pressure, and injection duration were the primary experimental variables. Results showed that temperature is the dominant factor governing ignition delay: increasing temperature from 520 °C to 580 °C reduced ID by 46.7% and its standard deviation by 62.8%. Increasing pressure shortened ID by 24.5% and reduced variability by 28.8%. In contrast, injection duration minimally affected ignition timing but increased accumulated heat release and maximum heat release rate by 37% and 20%, respectively. The time interval between ID and main combustion delay remained constant at approximately 0.30 ms across all conditions, indicating simultaneous advancement of ignition and combustion development. These findings demonstrate that ignition timing control (via temperature management) and combustion intensity control (via injection quantity) can be independently optimized, providing fundamental experimental data for the development of robust combustion-control strategies in dual-fuel marine engines.