The Interplay Between Combustion and Component Thermal Loading in Next-Generation Marine Engines Employing Reactivity-Controlled Compression Ignition

Energy transition demands cleaner and more efficient marine engines, accelerating the development of reactivity-controlled compression ignition (RCCI) concepts with multi-fuel capability. However, the coupling between combustion behavior and thermal loading in RCCI engines remains insufficiently understood due to limited experimental capabilities and the absence of integrated modeling tools. This study develops a rapid predictive framework that dynamically couples an in-house chemical-kinetics solver with a GT-Suite engine model and a finite-element wall thermal solver. The framework was calibrated against measurements from a single-cylinder research engine representative of the Wärtsilä 31DF medium-speed NG/LFO RCCI engine. It accurately captured component temperatures and combustion/performance parameters with RMS errors below 5% and cycle times under four minutes. The results show that RCCI operation introduces pronounced component temperature variations across the load range, creating challenges for thermal management and combustion control. Low-load combustion inefficiencies were linked to cylinder head thermal design rather than the conventional flame-quenching explanation. At high load, excessive pressure-rise rates amplified heat transfer demands, with exhaust-valve temperatures exceeding 780 K and posing pre-ignition risks. Increasing coolant temperature by 40 K reduced methane slip by 10% and advanced combustion by nearly 2 CAD, improving efficiency at low load, while coordinated lambda/fuel-blend control lowered peak combustion temperature by ~200 K at high load, mitigating thermal-induced pre-ignition without compromising performance or emissions.