The rapid advancement of thermal and mechanical engineering systems has intensified the need for working fluids with improved heat transfer performance, particularly in applications involving compact heat exchangers, rotating machinery, and lubrication systems. Conventional heat transfer fluids often exhibit low thermal conductivity, which limits their effectiveness under high thermal loads. In recent years, nanofluids and hybrid nanofluids have emerged as promising alternatives due to their enhanced thermophysical properties and improved heat transfer capabilities [1-5]. Hybrid nanofluids, formed by dispersing two or more different types of nanoparticles in a base fluid, have attracted significant attention owing to their ability to combine the favourable properties of individual nanoparticles. Numerous review studies report that hybrid nanofluids exhibit higher thermal conductivity, improved stability, and tunable rheological behaviour compared with mono-nanofluids, making them suitable for advanced thermal management applications [1-5]. These advantages have motivated extensive numerical and experimental investigations into hybrid nanofluid flow and heat transfer in various configurations. Among different flow control mechanisms, magnetohydrodynamic (MHD) effects play an important role in electrically conducting hybrid nanofluids. The application of a magnetic field introduces a Lorentz force that significantly alters the momentum and thermal transport characteristics of the flow. Several studies have examined MHD hybrid nanofluid flow over stretching surfaces, rotating disks, and between parallel plates, demonstrating that magnetic fields can effectively regulate velocity, temperature distribution, and entropy generation [6-11]. Rotating flow configurations are of particular importance in engineering systems such as bearings, turbines, and lubrication devices. Recent investigations have focused on hybrid nanofluid flow in rotating geometries, including rotating disks and parallel plates, under the combined influence of MHD effects and thermal radiation. These studies reveal that rotation induces Coriolis forces that strongly couple the momentum equations and significantly influence the secondary flow and heat transfer characteristics [11-14]. Thermal radiation and viscous dissipation become increasingly significant in high-temperature and high-shear-rate environments. Many researchers have incorporated radiative heat transfer and viscous dissipation into hybrid nanofluid models and reported substantial modifications in temperature profiles, thermal boundary layer thickness, and heat transfer rates [15-25]. Furthermore, internal heat generation or absorption has been shown to play a crucial role in controlling the thermal behaviour of hybrid nanofluids in confined geometries [25-30].

Engine-oil-based hybrid nanofluids have gained attention due to their relevance in lubrication and cooling applications. Studies indicate that the addition of nanoparticles to engine oil can significantly enhance its thermal conductivity and heat transfer performance without severely compromising its lubricating properties [30,31]. Such findings highlight the potential of engine-oil-based hybrid nanofluids in rotating and porous systems. In many practical applications, the presence of a porous medium further modifies the flow resistance and heat transfer behaviour. Recent investigations have shown that porous media significantly affect MHD hybrid nanofluid flow, particularly when combined with rotation, radiation, and viscous dissipation effects [32-34]. However, most existing studies consider these effects separately or in limited combinations.

Despite the growing body of literature, a comprehensive study that simultaneously examines the effects of rotation, magnetohydrodynamics, porous medium resistance, viscous dissipation, thermal radiation, and internal heat generation on TiO?-CoFe?O?/engine-oil hybrid nanofluid flow between rotating parallel plates remains scarce. The present study aims to address this gap by developing a detailed mathematical model and providing numerical insights into the coupled flow and heat transfer characteristics under these combined physical mechanisms.

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