대형 보어 LNG 이중연료(DF) 엔진에서 실린더 보어의 기하학적 스케일링 효과가 연소 안정성과 노킹 민감도에 미치는 영향 = Geometric Scaling Effects of Cylinder Bore on Combustion Stability and Knock Sensitivity in Large Bore LNG Dual Fuel Engines

다국어 초록 (Multilingual Abstract)

Large bore LNG dual fuel (DF) engines are increasingly adopted in marine propulsion systems due to their high thermal efficiency and reduced regulated emissions. However, as the cylinder bore increases, combustion stability and knock propensity become more sensitive, while the isolated geometric effects of bore scaling governing these trends remain insufficiently clarified. In particular, the pure effect of bore scaling on wall heat loss, in-cylinder thermal conditions, and knock-related combustion characteristics has not been systematically investigated under identical operating conditions.
In this study, a CFD based geometric scaling framework was developed and applied to investigate the influence of cylinder bore variation on combustion behavior and knock sensitivity in a four stroke LNG DF diesel engine. A reference engine geometry with a 350 mm bore was defined, and the bore diameter was systematically varied while maintaining identical stroke, compression ratio, combustion chamber geometry, valve timing, fuel properties, and injection conditions to isolate pure geometric effects. A sector based three dimensional in cylinder CFD model with dynamic mesh treatment was employed.
The results indicate that increasing the bore diameter reduces the wall-area-to-volume ratio, leading to a reduction in relative wall heat loss and enhanced thermal energy retention in the core region. Consequently, the in cylinder core gas temperature increases near the end of compression and during the early combustion phase, which promotes higher heat release rates, advanced combustion phasing, and increased maximum pressure rise rates. As a result, the knock margin decreases and knock sensitivity increases under identical operating conditions. Rather than providing absolute quantitative predictions, this study presents a physically consistent, trend oriented framework to interpret bore-scaling effects on combustion stability and knock sensitivity in large bore LNG DF engines. The proposed framework provides a fundamental guideline for subsequent high-fidelity CFD simulations and experimental investigations aimed at knock mitigation and combustion control.