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There is a wide spectrum of cast ferrous heat resistant alloys available for exhaust component applications such as exhaust manifolds and turbocharger housings. Generally speaking, the ferrous alloys can be divided into four groups including: ferritic cast irons, austenitic cast irons, ferritic stainless steels, and austenitic stainless steels. Selection of a suitable alloy usually depends on a number of material properties meeting the requirements of a specific application. Ferritic cast irons continue to be an important alloy for exhaust manifolds and turbocharger housings due to their relatively low cost. A better understanding of the alloying effects and graphite morphologies of ferritic cast irons are discussed and their effect on material behavior such as the brittleness at medium temperatures is provided. The nickel-alloyed austenitic cast irons, also known as Ni-resist, exhibit stable structure and improved high-temperature strength compared to the ferritic cast irons.

The cyclic plasticity of a typical exhaust manifold material has been successfully characterized using a unified constitutive model based on the models developed by Sehitoglu and his co-workers [1-2]. Both monotonic tensile and cyclic strain controlled fatigue tests were performed at temperatures ranging from ambient to 800 °C to evaluate the material constants in the model. In this model, the isotropic hardening is ignored due to its minor effect upon the selected cast iron, which simplified the data processing. The model predictions are satisfactory for a wide temperature range (23-800 °C), and the strain rates covered (0.5-50 %/min).

Strain-controlled low-cycle fatigue (LCF) experiments were conducted on ductile cast iron at total strain rates of 1.2/min, 0.12/min and 0.012/min in a temperature range of RT ~ 800°C. An integrated creep-fatigue (ICF) life prediction framework is proposed, which embodies a deformation mechanism based constitutive model and a thermomechanical damage model. The constitutive model is based on the decomposition of inelastic deformation into plasticity and creep mechanisms, which can describe both rate-independent and rate-dependent cyclic responses under wide strain rate and temperature conditions. The damage model takes into consideration of i) plasticity-induced fatigue, ii) intergranular embrittlement, iii) creep and iv) oxidation. Each damage form is formulated based on the respective physical mechanism/strain.

A study has been conducted to quantify the typical internal surface roughness of a cast iron exhaust manifold. In addition, the range of surface roughness values that can be obtained with various manufacturing methods was measured. Initial investigations were conducted to measure the effect of a range of surface roughness values on the performance of the engine system, specifically torque and the thermal losses through the exhaust manifold walls. Several manifold geometries were used to represent a variety of actual manifold applications, including designs that were subjected to tight packaging constraints. Physical tests were used to show that large variations in surface roughness resulted in modest changes in manifold component pressure losses. A simulation tool was used to predict that modest improvements in manifold pressure losses have little impact on engine output.

A strategy for performing transient computational fluid dynamics simulations of systems consisting of exhaust manifolds and close-coupled catalytic converters is described. The motivation for performing such a simulation is discussed, with reference to the literature, and a description of the modelling approach is given. The differences between steady-state and transient figures of merit for catalyst utilization and sensor positioning are discussed, including the development of a novel figure of merit for sensor positioning which is suitable for implementation in a transient simulation. A comparison between steady-state and transient simulation results for a typical simulation case is shown. Other simulation features for future development are discussed briefly.

In this paper, both standard and constrained thermomechanical fatigue (TMF) tests were conducted on a high silicon ductile cast iron (DCI). The standard TMF tests were conducted with independent control of mechanical strain, out-of-phase (OP) and in-phase (IP) strain, and temperature in the range from 300 to 800°C. The constrained TMF tests were conducted with various constraint ratios of 100%, 70%, 60% and 50% at the temperature ranges of 160 to 600°C and 160 to 700°C. Based on a material model as calibrated with low-cycle fatigue (LCF) data of DCI, finite element analyses (FEA) of the above TMF tests were carried out with Abaqus. A damage mechanism-based lifetime model was integrated into a C++ API code to post-process the Abaqus output results. Simulation predictions show good agreement with experiments for stress-strain responses and lifetime under different TMF conditions.

The heat rejection rates and skin temperatures of a liquid cooled exhaust manifold on a 3.5 L Gasoline Turbocharged Direct Injection (GTDI) engine are determined experimentally using an external cooling circuit, which is capable of controlling the manifold coolant inlet temperature, outlet pressure, and flow rate. The manifold is equipped with a jacket that surrounds the collector region and is cooled with an aqueous solution of ethylene-glycol-based antifreeze to reduce skin temperatures. Results were obtained by sweeping the manifold coolant flow rate from 2.0 to 0.2 gpm at 12 different engine operating points of increasing brake power up to 220 hp. The nominal coolant inlet temperature and outlet pressure were 85 °C and 13 psig, respectively. Data were collected under steady conditions and time averaged. For the majority of operating conditions, the manifold heat rejection rate is shown to be relatively insensitive to changes in manifold coolant flow rate.