Analysis of Temperature Swing Thermal Insulation for Performance Improvement of Diesel Engines

摘要

Insulating combustion chamber surfaces with thermal barrier coatings (TBCs) provides thermal efficiency improvement when done appropriately. This article reports on insulation heat transfer, engine performance characteristics, and damage modelling of "temperature swing" TBCs. "Temperature swing" insulation refers to the insulation material applied on surfaces of combustion chamber walls that enables selective manipulation of its surface temperature profile over the four strokes of an engine cycle. A combined GT Suite-ANSYS Fluent simulation methodology is developed to investigate the impact of thermal properties and insulation thickness for a variety of TBC materials for its "temperature swing" characteristics. This one-dimensional transient heat conduction analyses and engine cycle simulations are performed using scaled-down thermal properties of yttria-stabilized zirconia. The impact of heat insulation on thermal efficiency is quantified, and it is found that when insulation rate of 48% is achieved by applying coatings only on the piston top surface, engine thermal efficiency can be improved by up to 1.5%. Subsequently, the impact of TBC properties on engine thermal efficiency and volumetric efficiency at different engine speeds (frequency) and loads is discussed. Subsequent to IC engine performance prediction, a parametric analysis is performed for studying various conditions of damage in TBCs. It is often found that many TBCs show promise at time zero, that is, during initial testing, and performance and life degrades over a period of time. Hence, a TBC should have a long life, be reliable, account for manufacturing variations, and be inexpensive. Johnson-Cook damage model is used for which material parameters found based on experimental data are reported in literature. Effects of thickness, modulus of elasticity, and thermal conductivity are studied on damage and strain to fracture in TBC. It is found that damage is maximum for higher thermal conductivity, higher TBC thickness, and higher elastic modulus.