Nucleate Boiling Identification and Utilization for Improved Internal Combustion Engine Efficiency

Abstract

Internal combustion engines continue to become more compact and require greater heat rejection capacity. This demands research in cooling technologies and investigation into the limitations of current forced convection based cooling methods. A promising solution is the cooling strategy optimized with nucleate boiling to help meet these efficiency and emission requirements. Nucleate boiling results in an increased heat transfer coefficient, potentially an order of magnitude greater than forced convection, thereby providing improved cooling of an engine. This allows reduced coolant flow rates, increased efficiency, and reduced engine warm-up time. A study was conducted to characterize nucleate boiling occurring in the cooling passages of an IC engine cylinder head in a computational as well as experimental domain. The simulation was conducted to understand the physics of boiling occurring in an engine cooling passage and provide support for a potential boiling detection method. The computational fluid dynamics (CFD) simulation was performed for a simplified, two dimensional domain that resembled an engine cooling passage. The simulation results were followed by investigations of a pressure-based detection technique which was proven to be an effective method to detect boiling. An experimental test rig was used which consisted of a single combustion chamber section from a 5.4L V8 cylinder head. Water was used as the coolant. Results demonstrate the phase change physics involved in the boiling in an engine cooling passage, pressure variations in the coolant, heat flux data associated with the onset of nucleate boiling, and a comparison with existing boiling curves for water. Results of the simulation and experimental setup indicated that the change in energy and accompanying increase in pressure values can be related to bubble dynamics and thus provides a potential method to accurately detect nucleate boiling occurrence in an engine cooling system.