Showing 3 results for Cylinder Heads and Valves Bridge
H. Ashuri,
Volume 5, Issue 2 (6-2015)
Abstract
Loading conditions and complex geometry have led the cylinder heads to become the most challenging parts of diesel engines. One of the most important durability problems in diesel engines is due to the cracks valves bridge area. The purpose of this study is a thermo-mechanical analysis of cylinder heads of diesel engines using a two-layer viscoelasticity model. The results of the thermo-mechanical analysis indicated that the maximum temperature and stress occurred in the valves bridge. The results of the finite element analysis correspond with the experimental tests, carried out by researchers, and illustrated the cylinder heads cracked in this region. The results of the thermo-mechanical analysis showed that when the engine is running the stress in the region is compressive caused by the thermal loading and combustion pressure. When the engine shut off the compressive stress turned into the tensile stress because of assembly loads. The valves bridge was under the cyclic tensile and compressive stress and then is under low cycle fatigue. After several cycles the fatigue cracks will appear in this region. The lifetime of this part can be determined through finite element analysis instead of experimental tests. Viscous strain was more than the plastic strain which is not negligible.
H. Ashuri,
Volume 7, Issue 2 (6-2017)
Abstract
This paper presents finite element analysis (FEA) of a coated and uncoated cylinder heads of a diesel engine to examine the distribution of temperature and stress. A thermal barrier coating system was applied on the combustion chamber of the cylinder heads, consists of two-layer systems: a ceramic top coat (TC), made of yttria stabilized zirconia (YSZ), ZrO2-8%Y2O3 and also a metallic bond coat (BC), made of Ni-Cr-Al-Y. The coating system in this research comprises 300 μm zirconium oxide TC and 150 μm BC. The three-dimensional model of the cylinder heads was simulated in abaqus software and a two-layer viscoplasticity model was utilized to investigate the elastic, plastic and viscous behavior of the cylinder heads. The elastic and plastic properties of BC and TC layers were considered and the effect of thermal barrier coatings on distribution of temperature and stress was investigated. The aim of this study is to compare the distribution of temperature and stress in the coated and uncoated cylinder heads under thermo-mechanical loads. The results of FEA showed that the thermal barrier coating system reduces the temperature about 53°C because of its lower thermal conductivity. As a result, the cylinder head tolerates lower temperature and fatigue life will increase. The results of thermo-mechanical analysis indicated that the stress in the coated cylinder head decreased approximately 24 MPa for the sake of depletion of temperature gradient which can lead to higher fatigue lifetime. Viscous strain was significant and its amount is not negligible.
Hojjat Ashouri,
Volume 12, Issue 3 (9-2022)
Abstract
Loading conditions and complex geometry have led the cylinder heads to become the most challenging parts of diesel engines. The aim of this study is to compare the distribution of temperature and stress in the aluminum and magnesium cylinder heads under thermo-mechanical loads. The three-dimensional model of the cylinder heads was simulated in abaqus software and a two-layer viscoplasticity model was utilized to investigate the elastic, plastic and viscous behavior of the cylinder heads. The temperature and stress results of magnesium alloy was compared to aluminum alloy results. The results of finite element analysis (FEA) showed that surface temperature of the magnesium cylinder heads is about 23°C lower than the aluminum cylinder heads. As a result, the fatigue lifetime of the magnesium cylinder heads can be improved in comparison to the aluminum cylinder heads. The thermo-mechanical analysis showed that the magnesium cylinder heads tolerate less tensile and compressive cyclic stress compared to the aluminum cylinder heads. The stress reduction value in the magnesium cylinder heads was about 10 MPa which can lead to higher fatigue lifetimes in comparison to the aluminum cylinder heads.
