NUMERICAL AND EXPERIMENTAL APPROACH FOR COOLING SYSTEM OPTIMIZATION IN AN AIR-COOLED CNG ENGINE
Aluminum alloy is a popular choice of material for cylinder head of an internal combustion (IC) engine. Aluminum alloy, when exposed to the high temperature for extended period of time, is vulnerable to a drastic loss in hardness. Hence it is important to maintain the combustion chamber wall temperatures within acceptable limit to ensure the durability of engine components. Efficient cooling system plays an important role to achieve this objective. In the present work, an air-cooled CNG is taken up for enhancement in engine cooling system. A 1D gas-exchange model is created to generate the thermal boundary conditions required for Computational Fluid Dynamics (CFD) analysis. In-cylinder temperatures predicted by 1D analysis are validated with the experimental templug data. A steady-state 3D Conjugate Heat Transfer (CHT) model, that uses the predicted in-cylinder temperatures as a spatially varying boundary condition, is created to predict the convective heat transfer between engine fins and cooling air. To predict the air draft to the engine, a flywheel-mounted fan is modeled using the Moving Reference Frame (MRF) approach. Fin temperature predicted using this procedure is validated for a baseline case with the thermocouple data. Predicted Heat Transfer Coefficients (HTCs) are mapped onto the Finite Element Analysis (FEA) model to accurately predict the heat transfer through contacts and temperatures at various locations in the cylinder head. Baseline FEA results are also validated with the experimental in-cylinder temperature data. To address the overheating, shroud and cylinder head designs are identified as improvement areas. The above numerical procedure is repeated to estimate the effectiveness of modified cooling system. Tests are also conducted with modified shroud and cylinder head (produced by rapid prototyping); they show significant improvement in the overall cooling of the engine.