Thermal and Conjugate Heat Transfer Analysis of Exhaust Manifold of Multi-cylinder IC Engine

The exhaust manifold of multi cylinder IC engine is kept in between the engine block and the catalytic converter. So the exhaust manifold is exposed to very high temperature and care should be taken at the critical zone during the design stage. At several critical zones of the exhaust manifold, large compressive deformations are generated at elevated temperatures and tensile stresses remain at cold conditions. The thermal analysis will help in estimating the deformations and stress concentrations due to thermal loads. Therefore, the main aim of this study is to perform thermal analysis and conjugate heat flow analysis of an exhaust manifold of a multi-cylinder engine. The 3D model is generated using SolidWorks and analysis is carried out using Ansys workbench. Materials like grey C.I., aluminium nitride, silicon nitride, and stainless steel are used in this analysis. The results of total heat flux, directional heat flux and temperature distribution were compared. Silicon nitride material is suggested to be the suitable material for engine exhaust manifolds based on the material mechanical properties and thermal distribution-related thermal stress developed on the exhaust manifold.

Flow characterisation in an exhaust manifold of a single-cylinder internal combustion engine (ICE)

This paper presents an investigation of flow characteristic inside the exhaust manifold that were designed with different bending angle (BA), bending radius (BR) and pipe diameter (Dp ). Five exhaust manifold models were developed and analysed by the computational fluid dynamic (CFD) method. Accordingly, the pressure distribution, velocity streamline and backpressure values were observed. The simulation results showed a different flow pattern for all five models, indicating the manifold design affect the flow characteristic inside the exhaust system. The results demonstrated that the pressure distribution inside the exhaust manifold is influencing its velocity streamline pattern, that directly effecting the outlet velocity of the exhaust gas. From this work, a small bending angle with a short straight pipe has led to a smoother exhaust flow and even exhaust velocity across the model. The results obtained from the simulation can be used as a guide to improve the understanding of the flow behaviour in the manifolds and might be used to improve the manifold design.

CFD and Thermal Analysis of Exhaust Manifold and Exhaust Header for a 6 Cylinder Inline Engine: A Review

Exhaust Manifold and Exhaust Header is one of the important additives of IC engine for enhancing the volumetric performance. The volumetric performance of the engine may be expanded with the aid of using decreasing the backpressure and growing the exhaust pace with inside the exhaust manifold and header. These studies examine the float via unique fashions of exhaust manifold and exhaust header the use of CFD and Thermal evaluation for a 6 cylinder inline engine. The layout of exhaust manifold is changed to get gold standard geometry. The evaluation consequences of fashions are as compared for returned stress and pace of exhaust fuel line. By evaluating the consequences of fashions the lower in returned stress is located which make sure development in volumetric performance of the engine. Keywords: Exhaust Manifold, Exhaust Header, CFD Analysis, Thermal Analysis, 6-Cylinder Inline Engine

Prediction of Exhaust System Vibration Through Harmonic Analysis & High Cycle Fatigue Life Evaluation

Exhaust system typically experiences vibration during engine operating conditions due to periodic disturbing forces (firing force and inertia force) which are generated from the engine. Natural frequency of the exhaust system gets excited due to the periodic forces causing resonance which often leads to high cycle fatigue (HCF) failure. Turbocharger is a part of exhaust system and it is mounted on the exhaust manifold. The periodic forces are transferred from engine base (Cylinder head and Block) and these forces gets amplified to overhanging components like exhaust system turbocharger. It is an industrywide practice to perform modal analysis to determine the natural frequencies of the system. However, modal analysis cannot predict the intensity with which the system would vibrate. Thus, we need to make some assumptions about the system vibration ‘g’ levels. Based on accuracy of this assumption, we may end up under-designing or over-designing the system. Harmonic analysis enables us to accurately predict the ‘g’ level at turbocharger using experimental cylinder head base excitations. After recording the correlation with experimental data in many cases it was found that this approach further aided in establishing damping constant factor of the exhaust manifold at elevated temperature. This analysis process has been validated with multiple cases as it has turned out to be a potential approach while doing design risk assessments and optimizing the engine vibration validation efforts. The benefit of prediction of exhaust system vibration level allows us to avoid iterative design process in the early stage of product development thus optimizing the design by taking advantage of shifting the natural frequency of exhaust system to lower source excitation (cylinder head). This saves vast amount of simulation lead time. Another benefit of this process is that the prediction of resonance condition of exhaust system through simulation helps us to estimate the fatigue life against the predicted ‘g’ level.

On-Engine Expansion Measurement of Exhaust Manifold for Calibrating Thermo-Mechanical Fatigue FEA Model

An attempt was made as part of this work to acquire on-engine measurements to identify how closely current Finite Element Analysis (FEA) models replicate actual on-engine exhaust manifold behavior. Further correlation study with FEA models was performed to understand and eliminate the gaps to improve the overall FEA process. Dry cast iron exhaust manifolds experience thermo-mechanical fatigue (TMF) during engine operation. This is one of the critical failure modes. Literature is available to perform TMF assessment of exhaust manifold e.g. [1–6]. However, it is difficult to accurately predict TMF life of exhaust manifold in FEA due to dependency on multiple factors such as non-linear material behavior [3], temperature dependent material behavior, oxidation effect, creep effect, accuracy in prediction of metal temperatures and joint friction effects. Typically, non-linear material models, creep effects and oxidation effects are accounted by advanced fatigue processing software. Non-linear material models account for material and for temperature dependent non-linearity [4]. These non-linear material model and fatigue parameters are often developed using uniaxial specimen level testing. These doesn’t account for all the complexity during on-engine test due to factors such as friction and bolt loads that can influence manifold behavior. FEA processes for exhaust manifolds are seldom calibrated with on-engine measurements due to the complexity of obtaining these measurements in an environment that has severe temperatures and vibrations. The correlation study highlighted that exhaust manifold was over constrained by excessive clamping in FEA. This raised question on the gasket coefficient of friction (COF) and working preloads. These settings were investigated to get better correlation. Using reduced COF and non-linear material model for manifold capscrews, helped to achieve better correlation. Replacing material properties of manifold capscrews with nonlinear data provided capability to simulate localized yielding of capscrews and hence the corresponding load loss. Using these new settings for few other case studies also showed improvement in correlation of manifold warpage and thermal fatigue life prediction. Outcome of this work was a refined FEA approach which showed better FEA to Test correlation for exhaust manifold subject to thermal loading.

Development of Simplified Analysis Process for Multidisciplinary Design Optimization (MDO) of Exhaust Manifold During Concept Stage

The exhaust manifold is one of the key components of an engine exhaust system. Exhaust manifold simulations are time-consuming as they require modeling of complex thermal loading and multiple non-linearities like friction and plasticity. This proves to be a big constraint for using Multidisciplinary Design Optimization (MDO) for exhaust manifolds as it involves running a large number of models specified by a Design of Experiments (DOE). Also, during the initial phase of design development, it seems reasonable to compromise the accuracy of simulations at the cost of speed for getting correct feedback on design direction. Hence, the main objective of the current work was to a develop simplified analysis process for Thermomechanical Fatigue (TMF) and modal analysis of exhaust manifold. At the concept stage, due to the lack of availability of accurate thermal Boundary Conditions (BCs) and the goal to simplify modeling, thermal BCs are assumed with the help of thermal data history instead of accurate thermal BCs from test cells. Similarly, other aspects such as ‘level of component assembly required’, ‘mechanical loading’, and ‘outputs to be monitored for making design decisions were also investigated to come up with a simplified approach. The proposed approach was quick compared to the conventional one. This approach was implemented on a few heavy-duty and mid-range engine programs to check repeatability. It was observed that the proposed analysis approach provides correct design direction with a significantly reduced computational time of up to 80%. Incorporating the simplified approach for the MDO process has made it more practical and feasible for implementation during the concept design cycle in the early stage of an engine development program.