<![CDATA[Improving the air-fuel mixing process remains a practical route for increasing the combustion quality of naturally aspirated marine diesel engines. This study evaluates a passive cyclone installed in the intake manifold of a single-cylinder Yanmar TF-85 MH engine using three-dimensional computational fluid dynamics and experimental validation. Twenty-seven cyclone geometries were generated from combinations of vane height, vane length, and twist angle, and simulations were performed at 1,600, 1,800, and 2,000 rpm. The numerical model employed an RNG k-epsilon turbulence formulation, moving-valve and piston domains, a chemical-kinetics combustion solver, and a B40 surrogate composed of methyl decanoate and n-dodecane. The optimum geometry, designated GD 11560, increased turbulent kinetic energy from 330.35 to 367.34 m2/s2, or 11.20%, while reducing the inducted air mass by 4.12%. The indicated mean effective pressure increased by 1.88% at 1,600 rpm and 0.36% at 1,800 rpm, but decreased by 0.87% at 2,000 rpm. Maximum combustion temperature and pressure rose by 2.43% and 1.08%, respectively, at 1,600 rpm. Validation errors remained below 5%. The cyclone therefore improves low-to-medium-speed combustion through stronger axial-tangential motion, although its flow restriction becomes important at high speed.]]>
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