The development of thermal stress in the exhaust manifold of a gasoline engine is considered.The problem is addresses in the frame of a combined approach wherefluid and structure are coupled using the GT-POWER and STA...The development of thermal stress in the exhaust manifold of a gasoline engine is considered.The problem is addresses in the frame of a combined approach wherefluid and structure are coupled using the GT-POWER and STAR-CCM+software.First,the external characteristic curve of the engine is compared with a one-dimen-sional simulation model,then the parameters of the model are modified until the curve matches the available experimental values.GT-POWER is then used to transfer the inlet boundary data under transient conditions to STAR-CCM+in real-time.The temperature profiles of the inner and outer walls of the exhaust manifold are obtained in this way,together with the thermal stress and thermal deformation of the exhaust manifold itself.Using this information,the original model is improved through the addition of connections.Moreover,the local branch pipes are optimized,leading to significant improvements in terms of thermal stress and thermal deforma-tion of the exhaust manifold(a 7%reduction in the maximum thermal stress).展开更多
Si-Mo vermicular iron is an ideal material for exhaust manifold that works in high temperature and thermal cycle conditions because its properties of thermal fatigue resistance and thermal distortion resistance are si...Si-Mo vermicular iron is an ideal material for exhaust manifold that works in high temperature and thermal cycle conditions because its properties of thermal fatigue resistance and thermal distortion resistance are significantly better than that of gray cast iron and nodular iron. This paper explains that the vermicularity of Si-Mo vermicular iron is better to be controlled approximately to 50% for the applications of exhaust manifold castings, and generalizes the successful experience of vermicularizing technique that uses sandwich (pour over) process combining with cored-wire injection in trough process together, and uses rare earths-magnesium-silicon as vermicularizing alloy in Disa high speed molding line and automatic plug rod air pressure pouring furnace. In addition, this paper also describes the method to solve the shrinkage hole and porosity defects in the exhaust manifold production.展开更多
The effect of fin attachment on the thermal stress reduction of exhaust manifold of an off road diesel engine(Komatsu HD325-6) was investigated.For doing this,coupled thermo-fluid-solid analysis of exhaust manifold of...The effect of fin attachment on the thermal stress reduction of exhaust manifold of an off road diesel engine(Komatsu HD325-6) was investigated.For doing this,coupled thermo-fluid-solid analysis of exhaust manifold of the off road diesel engine was carried out.The thermal analysis,including thermal flow,thermal stress,and the thermal deformation of the manifold was investigated.The flow inside the manifold was simulated and then its properties including velocity,pressure,and temperature were obtained.The flow properties were transferred to the solid model and then the thermal stresses and the thermal deformations of the manifold under different operating conditions were calculated.Finally,based on the predicted thermal stresses and thermal deformations of the manifold body shell,two fin types as well as body shell thickness increase were applied in the critical induced thermal stress area of the manifold to reduce the thermal stress and thermal deformation.The results of the above modifications show that the combined modifications,i.e.the thickness increase and the fin attachment,decrease the thermal stresses by up to 28% and the contribution of the fin attachment in this reduction is much higher compared to the shell thickness increase.展开更多
Ductile cast irons are used as high temperature materials in internal combustion engines,because they are microstructurally stable at high operating temperatures. SiMo granular graphite cast irons contain Fe2MoC and M...Ductile cast irons are used as high temperature materials in internal combustion engines,because they are microstructurally stable at high operating temperatures. SiMo granular graphite cast irons contain Fe2MoC and M6C carbide precipitates due to their higher concentration of both silicon and molybdenum. The microstructure of these cast irons consists of carbides dispersed within the ferrite matrix. The microstructural change and the crack formation mechanism in manifolds produced from SiMo ductile iron are studied. Chemical analysis,optical and scanning electron microscope studies have been completed and evaluated.展开更多
The thermal fatigue cracking behavior of high Si-Mo nodular cast iron （NCI） is investigated by means of optical microscope （OM）, scanning electron microscope （SEM） and energy dispersive spectroscope （EDS）, in ...The thermal fatigue cracking behavior of high Si-Mo nodular cast iron （NCI） is investigated by means of optical microscope （OM）, scanning electron microscope （SEM） and energy dispersive spectroscope （EDS）, in order to find a new material used in exhaust manifolds in First Automotive Works （FAW） .Nodular cast irons with silicon content about 4.7% , in combination with up to 1.1% molybdenum , were produced by Jilin University and FAW. The repeated heating / cooling test was performed under cyclic heating at various maximum heating temperatures （Tmax） ranging from 800to 900℃.Experimental results indicate that the thermal fatigue cracking resistance of high Si-Mo NCI decreases with increasing the maximum heating temperature.The periods for crack initiation are 24-36 , 40-50and 70-90times associated with heating temperature of 900 , 850and 800℃ , respectively , when the holding time is about 10min at Tmax.When thermal fatigue cracking occurs , the cracking always initiates at the bigger surface of specimen.The major positions of cracks propagation are generally at the eutectic oxide boundary region and the region of the graphite disappearance.At the same time , the oxidation may accelerate crack initiation and propagation.On the other hand , micro-crack number varied from large to little because of shielding effect.As exhaust manifolds , the reasonable working temperature of high Si-Mo NCI is no more than 840℃ by test and analysis.展开更多
基金supported by the Basic Ability Improvement Project for Young and Middle-Aged Teachers in Guangxi Universities,Project No.2021KY0792.
文摘The development of thermal stress in the exhaust manifold of a gasoline engine is considered.The problem is addresses in the frame of a combined approach wherefluid and structure are coupled using the GT-POWER and STAR-CCM+software.First,the external characteristic curve of the engine is compared with a one-dimen-sional simulation model,then the parameters of the model are modified until the curve matches the available experimental values.GT-POWER is then used to transfer the inlet boundary data under transient conditions to STAR-CCM+in real-time.The temperature profiles of the inner and outer walls of the exhaust manifold are obtained in this way,together with the thermal stress and thermal deformation of the exhaust manifold itself.Using this information,the original model is improved through the addition of connections.Moreover,the local branch pipes are optimized,leading to significant improvements in terms of thermal stress and thermal deforma-tion of the exhaust manifold(a 7%reduction in the maximum thermal stress).
文摘Si-Mo vermicular iron is an ideal material for exhaust manifold that works in high temperature and thermal cycle conditions because its properties of thermal fatigue resistance and thermal distortion resistance are significantly better than that of gray cast iron and nodular iron. This paper explains that the vermicularity of Si-Mo vermicular iron is better to be controlled approximately to 50% for the applications of exhaust manifold castings, and generalizes the successful experience of vermicularizing technique that uses sandwich (pour over) process combining with cored-wire injection in trough process together, and uses rare earths-magnesium-silicon as vermicularizing alloy in Disa high speed molding line and automatic plug rod air pressure pouring furnace. In addition, this paper also describes the method to solve the shrinkage hole and porosity defects in the exhaust manifold production.
文摘The effect of fin attachment on the thermal stress reduction of exhaust manifold of an off road diesel engine(Komatsu HD325-6) was investigated.For doing this,coupled thermo-fluid-solid analysis of exhaust manifold of the off road diesel engine was carried out.The thermal analysis,including thermal flow,thermal stress,and the thermal deformation of the manifold was investigated.The flow inside the manifold was simulated and then its properties including velocity,pressure,and temperature were obtained.The flow properties were transferred to the solid model and then the thermal stresses and the thermal deformations of the manifold under different operating conditions were calculated.Finally,based on the predicted thermal stresses and thermal deformations of the manifold body shell,two fin types as well as body shell thickness increase were applied in the critical induced thermal stress area of the manifold to reduce the thermal stress and thermal deformation.The results of the above modifications show that the combined modifications,i.e.the thickness increase and the fin attachment,decrease the thermal stresses by up to 28% and the contribution of the fin attachment in this reduction is much higher compared to the shell thickness increase.
文摘Ductile cast irons are used as high temperature materials in internal combustion engines,because they are microstructurally stable at high operating temperatures. SiMo granular graphite cast irons contain Fe2MoC and M6C carbide precipitates due to their higher concentration of both silicon and molybdenum. The microstructure of these cast irons consists of carbides dispersed within the ferrite matrix. The microstructural change and the crack formation mechanism in manifolds produced from SiMo ductile iron are studied. Chemical analysis,optical and scanning electron microscope studies have been completed and evaluated.
基金Item Sponsored by Science and Technology Supporting Project of Jilin Province of China (2007301)
文摘The thermal fatigue cracking behavior of high Si-Mo nodular cast iron （NCI） is investigated by means of optical microscope （OM）, scanning electron microscope （SEM） and energy dispersive spectroscope （EDS）, in order to find a new material used in exhaust manifolds in First Automotive Works （FAW） .Nodular cast irons with silicon content about 4.7% , in combination with up to 1.1% molybdenum , were produced by Jilin University and FAW. The repeated heating / cooling test was performed under cyclic heating at various maximum heating temperatures （Tmax） ranging from 800to 900℃.Experimental results indicate that the thermal fatigue cracking resistance of high Si-Mo NCI decreases with increasing the maximum heating temperature.The periods for crack initiation are 24-36 , 40-50and 70-90times associated with heating temperature of 900 , 850and 800℃ , respectively , when the holding time is about 10min at Tmax.When thermal fatigue cracking occurs , the cracking always initiates at the bigger surface of specimen.The major positions of cracks propagation are generally at the eutectic oxide boundary region and the region of the graphite disappearance.At the same time , the oxidation may accelerate crack initiation and propagation.On the other hand , micro-crack number varied from large to little because of shielding effect.As exhaust manifolds , the reasonable working temperature of high Si-Mo NCI is no more than 840℃ by test and analysis.
