Numerical investigation of engine cooling using nanofluids

Abstract

The specific power densities of internal combustion engines tend to rise due to the competitive environment of the automotive industry. The increase in power density causes the thermal load on the engine components to increase as well. Improving specific fuel consumption is important for environmental sustainability. The present thesis aims mainly to evaluate the effect of nanoparticles on the engine's cooling performance. A detailed computation methodology was developed in order to correctly identify the temperature distribution in a natural gas fueled a single cylinder test engine. This study, unlike the methods discussed in the literature, is one of the first to examine in detail the effects of nanofluid use in internal combustion engines by using point based thermal boundary conditions in heat transfer calculations. The thermophysical properties of the nanofluids were determined using established methods from relevant literature. Based on the acquired nanoparticle properties, 60 simulation cases were conducted on a representative pipe model. These nanofluids advanced engineering fluids consist of a base fluid with suspended nanoparticles. In this study, water and a water-ethylene glycol mixture, both commonly used base fluids, were employed. The nanoparticles analyzed include Al2O3, CuO, and carbon black (CB). Nanoparticle volume concentrations varied between 1% and 4%, and simulations were conducted at coolant inlet temperatures of 25°C and 70°C to identify optimal nanofluid combinations. Key performance parameters such as indicated power, pumping losses, gross indicated work, frictional losses, and thermal losses were calculated. Engine efficiency values were also derived. The results were deemed consistent and reliable, as the calculated values closely aligned with existing literature. To support these analyses, CAD software was utilized to model the 3D geometry of the engine. A detailed combustion model was developed based on this geometry. Full cycle combustion simulations provided data on instantaneous heat transfer coefficients and temperature distributions near the cylinder walls. These transient values were converted into time independent forms through time averaging techniques and subsequently used in conjugate heat transfer (CHT) simulations. Simulation results demonstrated that nanofluid application in internal combustion engine cooling systems positively influenced the critical temperatures of engine components. However, increased pressure drops were observed due to the higher viscosities of the nanofluids. In this study, nanofluids were treated as homogeneous mixtures, and the effects of nanoparticle agglomeration and surface interactions were not considered. Future research should explore the impacts of these phenomena for more comprehensive analysis.