<![CDATA[Small direct-injection (DI) diesel engines remain indispensable for stationary power generation and small marine applications, where improving their output and fuel economy carries real practical value. This study evaluates the effect of modifying an intake manifold using a passive cyclone-type swirl generator on the performance of a marine diesel engine. The research presents a combined numerical and experimental approach to analyze the impact of the cyclone on engine power, torque, brake specific fuel consumption (BSFC), and thermal efficiency. Numerical simulations using Ansys Forte were initially conducted on 27 cyclone geometries to identify optimal turbulent kinetic energy (TKE) generation. Subsequently, experimental testing was performed on a Yanmar TF-85 single-cylinder diesel engine across varying speeds (1400–2200 RPM) and loads (1–3 kW). The numerical results indicated that the 110560-cyclone model generated the highest TKE (+11.20%) despite a slight reduction in mass flow. Experimental findings revealed that the cyclone significantly enhanced power and torque at low-to-medium speeds (1400–1800 RPM). Notably, at 1800 RPM, the optimal cyclone reduced BSFC by up to 20.8% and increased thermal efficiency by 26.3% compared to the standard intake. The enhanced TKE improved air-fuel homogenization, which successfully compensated for the slight volumetric efficiency drop at high speeds, providing practical evidence for intake-side swirl enhancement as an affordable route to improved marine engine performance]]>
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