Combustion Engine Cylinder Head Research Articles

Effects of Temperature on the Evolution of Yield Surface and Stress Asymmetry in A356-T7 Cast Aluminium Alloy.

As the electrification of vehicle powertrains takes prominence to meet stringent emission norms, parts of internal combustion engines like cylinder heads are subjected to an increased number of thermal load cycles. The cost-effective design of such structures subjected to cyclic thermo-mechanical loads relies on the development of accurate material models capable of describing the continuum deformation behaviour of the material. This study investigates the effect of temperature on the evolution of flow stress under cyclic loading in A356-T7 + 0.5% Cu cast aluminium alloy commonly used in modern internal combustion engine cylinder heads. The material exhibits peak stress and flow stress asymmetry with the stress response and flow stress of the material under compressive loading higher than under tension. This peak and flow stress asymmetry decrease with an increase in temperature. To compare this stress asymmetry against conventional steel, cyclic strain-controlled fatigue tests are run on fully pearlitic R260 railway steel material. To study the effect of mean strain on the cyclic mean stress evolution and fatigue behaviour of the alloy, tests with tensile and compressive mean strains of +0.2% and −0.2% are compared against fully reversed (Rε = −1) strain-controlled tests. The material exhibits greater stress asymmetry between the peak tensile and peak compressive stresses for the strain-controlled tests with a compressive mean strain than the tests with an identical magnitude tensile mean strain. The material exhibits mean stress relaxation at all temperatures. Reduced durability of the material is observed for the tests with tensile mean strains at lower test temperatures of up to 150 °C. The tensile mean strains at elevated temperatures do not exhibit such a detrimental effect on the endurance limit of the material.

Ductile iron optimization approach for mechanically and thermally loaded components

The mechanical and thermal properties of ferritic–pearlitic ductile irons vary widely according to their silicon and pearlite contents. Thus, different combinations of silicon and pearlite affect components’ lifetime under mechanical and thermal stress. An excellent example of the usage of such irons is combustion engine cylinder heads. They experience transient thermal loading (heating and cooling) during starting and stopping in addition to mechanical loading (combustion) during engine operation. An optimization approach and calculation models for the estimation of the optimal ductile iron composition are presented in this study. The approach allows selection of the most suitable base composition for subsequent analyses, such as casting simulation and final accurate finite element modelling and fatigue calculations.

Non-Standard T6 Heat Treatment of the Casting of the Combustion Engine Cylinder Head.

The introduction of new design solutions of cast components to the powertrain systems of passenger cars has resulted in an increased demand for optimization of mechanical properties obtained during heat treatment, assuring—at the same time—a suitable level of production capacity and limitation of manufacturing costs. In this paper, research results concerning non-standard T6 heat treatment of a combustion engine cylinder head made of AlSi7Cu3Mg alloy are presented. It has been confirmed that the optimal process of heat treatment of this component, taking into consideration the criterion of material hardness, involves solutioning at a temperature of 500 °C for 1 h, and then aging for 2 h at 175 °C. As a result, HBS10/1000/30 hardness in the range of 105–130 was obtained, which means an increase from 35% to 60% in comparison to the as-cast, depending on the position of the measurement and spheroidization of precipitations of eutectic silicon.

Effect of Strain Rate on the Deformation Behaviour of A356-T7 Cast Aluminium Alloys at Elevated Temperatures

Internal combustion engine downsizing and powertrain electrification trends in recent years have led to higher thermal loads on the cylinder head materials with an increased number of engine start–stop thermal load cycles. This requires designing cylinder heads that are resilient against thermomechanical fatigue damage. To reduce the developmental costs, reliable numerical models for use in computer-aided design approaches are required. Thus, a comprehensive understanding of the material deformation behaviour under loads mimicking in-service conditions is desired to make better engineering decisions. This study examines the effect of strain rate on the cyclic deformation behaviour of the A356-T7 + 0.5% Cu aluminium alloy commonly used in modern internal combustion engine cylinder heads. Samples extracted from the valve bridge areas of the cylinder heads are tested in strain-controlled fatigue tests. Samples are tested at strain rates of 1% s−1 and 10% s−1 at room temperature, 150 and 200 °C. The material exhibits increased isotropic hardening and softening rates and an increased number of cycles to failure at 10% s−1. The strain rate has a dramatic influence on the mean stress development at room temperature. The role of silicon particles in the fracture mechanism is investigated using electron microscopy techniques.

Influence of Cu addition on the heat treatment response of A356 foundry alloy

Strength and high-temperature performance are important properties in Al-Si-Mg alloys for power-train applications such as combustion engine cylinder head components in automotive industry. Addition of Copper (Cu) to Al-Si-Mg alloys is a common practice to obtain high strength as well as high temperature stability. However, Cu addition alters precipitation kinetics and precipitate types during artificial ageing, and consequently properties of final cast products. In this study, the effects of Cu on tensile properties in connection with precipitation and precipitate types, as observed through aging curves and TEM analysis, were investigated in Al-Si-Mg alloys having three different Cu contents in order to optimize Cu contents and heat treatment parameters. Higher solutionizing temperature enabled a significant increased Cu content in solid solution without any incipient melting of Cu-rich phases. A refinement of the precipitate microstructures was observed in the Cu-containing alloys, accompanied with a phase-change of the hardening needle precipitates. different precipitation kinetics and double aging peaks were observed during artificial aging in higher Cu containing alloys, which were correlated to higher strength than in the Cu-free alloy in underaged and peak aged conditions. Optimized Cu contents and heat treatment parameters were found with respect to a combination of strength and elongation.

The Time-Frequency Analysis Method Based on EMD White Noise Energy Density Distribution Characteristics of the Internal Combustion Engine Vibration

For the limitations of HHT of the internal combustion engine vibration signal analysis, and the problem of WVD cross-term suppression methods existing aggregation and cross-term component suppression conflicting, the time-frequency analysis method based on EMD white noise energy density distribution characteristics of the internal combustion engine vibration is proposed. First, the internal combustion engine vibration signal was decomposed into the independent series intrinsic mode function (IMF) with different characteristic time scales by using EMD decomposition method. Then, based on the energy density distribution characteristics of the white noise in EMD decomposition, used the distribution interval estimation curve of the IMFs energy density logarithm of white noise with the same length of the original signal as cordon for false pattern component, identified and eliminated false mode component of vibration signal IMFs component, analysised of each IMF with Wigner-Ville. Finally, the Wigner-Ville analysis results of each IMF were linear superposed in order to reconstruct the original signal time-frequency distribution. Simulation and engine vibration time-frequency analysis results show that this method has an excellent time-frequency characteristics, and can successfully extract feature information of the internal combustion engine cylinder head vibration signal.

A contribution to the understanding of thermomechanical fatigue sensitivities in combustion engine cylinder heads

Combustion engine cylinder heads are subject to frequent failure during prototype testing owing to thermomechanical fatigue (TMF). The complex interaction effects of the thermal and mechanical loads as well as the geometry and material on the cylinder head TMF behaviour have not been elaborated in detail. This paper serves to fill this gap by the utilization of finite element analysis and design-of-experiments methods on a passenger car engine model. The unique contributions of the temperature gradients, thermophysical material properties, and geometric dimensions such as the valve bridge width and thickness to the valve bridge TMF are pointed out with a certain abstraction level in modelling. The results indicate the vertical temperature difference on the flame deck valve bridge region as the dominant factor. While the valve bridge width and thickness are the geometric dominant influences, the thermal conductivity is the governing parameter among the material properties.

New thermo-mechanical analysis of cylinder heads using a multi-field approach

The results of a thermo-mechanical analysis of a natural gas, internal combustion engine cylinder head are presented in this paper. The results are pertinent to the evaluation of overheating damage in critical areas. The three-dimensional geometries of the cylinder head and the water jacket were modeled by means of a computer-aided engineering tool. Commercial finite element and computational fluid dynamics codes were used to compute details of mechanical stress in the head and flow details in the cylinder and cooling jacket, respectively. A six-cylinder, four-stroke diesel engine and a spark-ignition natural gas engine were modeled over a range of speeds at full load. Computed results, such as maximum allowable cylinder pressure, output power, BMEP and BSFC, were validated by experimented data in the diesel engine model. The results were in good agreement with experimental data. The results show high stresses at the valve bridge. Cylinder head temperatures and comparison of output power with high stress measurements, often exceeding the elastic limit, were found at the valve bridge.

Coupled Numerical Analysis of Quenching Process of Internal Combustion Engine Cylinder Head

The paper provides details about a newly developed method of coupled modelling procedure for the simulation of quenching process using a commercial Computational Fluid Dynamics (CFD) code AVL FIRE, followed by Finite Element Method (FEM) analysis to predict the stresses within the structure using ABAQUS. Boiling mass transfer process is triggered by submerging of a heated solid part into a subcooled liquid bath. As a result, two-phase flow with boiling phase change is handled using the Eulerian two-fluid method. Mass transfer effects are considered for both film and nucleate boiling regime. Separate computational domains constructed for the quenched solid part and the liquid (quenchant) domain are numerically coupled at the interface using the AVL-Code-Coupling-Interface (ACCI) feature. The program handles multiphase flow dynamics in the liquid domain in conjunction with the temperature evolution in the solid region in coupled fashion. The paper features numerical simulation results of a real cylinder head of a four cylinder gasoline engine. Comparison between measured and computed temperatures at different monitoring positions shows very good agreement for two cylinder head orientations. Significant nonuniformity in temperature distribution within the structure was observed, which is of great importance in evaluating residual stresses and fatigue patterns within the quenched object. The temperature field was mapped from volume-based computational grid used in CFD analysis onto a node-based grid used in FEM. Based on temperature distribution, the stresses and deformation within the cylinder head were calculated.

Modulation of ultrasound by vibration and its application for flaw detection

The paper gives an overview of a recent advancement in the development and implementation of an innovative nonlinear modulation technique for nondestructive testing. The theoretical and experimental investigations discovered that a weakly or incompletely bonded interface or contact-type defect causes the modulation of a probing high-frequency ultrasonic wave by low-frequency vibration. The vibration varies the contact area modulating the phase and amplitude of a higher-frequency probing wave passing through the interface. In the frequency domain the result of this modulation manifests itself as sideband spectral components with respect to the frequency of the probing wave. Such a modulation effect was observed experimentally for various materials (metals, composites, concrete, sandstones, glass) with various types of defects such as cracks, debondings, delaminations, and microstructural changes. Two modifications of the technique have been developed: vibromodulation (VM) and impact modulation (IM), employing cw and impact-induced vibrations, respectively. The examples of applications of these methods include crack detection in Boeing 767 steel fuse pins, combustion engine cylinder heads, sandstone, and glass. These methods also proved their effectiveness in evaluating bonding conditions in titanium and composite plates, as well as corrosion in reinforced concrete.

Flow in the coolant passages of an internal combustion engine cylinder head

Detailed measurements of the coolant flow field have been made in the water passages of the cylinder head of an internal combustion engine. They were obtained by casting a transparent acrylic model of the cylinder head and using a mixture of hydrocarbon fluids at a predetermined temperature and concentration which ensured that the refractive index of the fluid was identical to that of the acrylic. This arrangement allowed the use of laser Doppler velocimetry to measure local velocities throughout the cooling passages. The results show that the flow was unevenly distributed with around three quarters of the total passing through the exhaust-portside passages and larger coolant velocities close to the top of the head than close to the gas face. The results of this study aimed to assist the improvement of the specific cylinder head design.