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Technical Paper

Limitations of Sector Mesh Geometry and Initial Conditions to Model Flow and Mixture Formation in Direct-Injection Diesel Engines

2019-04-02
2019-01-0204
Sector mesh modeling is the dominant computational approach for combustion system design optimization. The aim of this work is to quantify the errors descending from the sector mesh approach through three geometric modeling approaches to an optical diesel engine. A full engine geometry mesh is created, including valves and intake and exhaust ports and runners, and a full-cycle flow simulation is performed until fired TDC. Next, an axisymmetric sector cylinder mesh is initialized with homogeneous bulk in-cylinder initial conditions initialized from the full-cycle simulation. Finally, a 360-degree azimuthal mesh of the cylinder is initialized with flow and thermodynamics fields at IVC mapped from the full engine geometry using a conservative interpolation approach. A study of the in-cylinder flow features until TDC showed that the geometric features on the cylinder head (valve tilt and protrusion into the combustion chamber, valve recesses) have a large impact on flow complexity.
Technical Paper

Strain Rate Effect on Martensitic Transformation in a TRIP Steel Containing Carbide-Free Bainite

2019-04-02
2019-01-0521
Adiabatic heating during plastic straining can slow the diffusionless shear transformation of austenite to martensite in steels that exhibit transformation induced plasticity (TRIP). However, the extent to which the transformation is affected over a strain rate range of relevance to automotive stamping and vehicle impact events is unclear for most third-generation advanced high strength TRIP steels. In this study, an 1180MPa minimum tensile strength TRIP steel with carbide-free bainite is evaluated by measuring the variation of retained austenite volume fraction (RAVF) in fractured tensile specimens with position and strain. This requires a combination of servo-hydraulic load frame instrumented with high speed stereo digital image correlation for measurement of strains and ex-situ synchrotron x-ray diffraction for determination of RAVF in fractured tensile specimens.
Technical Paper

A Mechanism-Based Thermomechanical Fatigue Life Assessment Method for High Temperature Engine Components with Gradient Effect Approximation

2019-04-02
2019-01-0536
High temperature components in internal combustion engines and exhaust systems must withstand severe mechanical and thermal cyclic loads throughout their lifetime. The combination of thermal transients and mechanical load cycling results in a complex evolution of damage, leading to thermomechanical fatigue (TMF) of the material. Analytical tools are increasingly employed by designers and engineers for component durability assessment well before any hardware testing. The DTMF model for TMF life prediction, which assumes that micro-crack growth is the dominant damage mechanism, is capable of providing reliable predictions for a wide range of high-temperature components and materials in internal combustion engines. Thus far, the DTMF model has employed a local approach where surface stresses, strains, and temperatures are used to compute damage for estimating the number of cycles for a small initial defect or micro-crack to reach a critical length.
Technical Paper

Constitutive Modeling and Thermomechanical Fatigue Life Predictions of A356-T6 Aluminum Cylinder Heads Considering Ageing Effects

2019-04-02
2019-01-0534
Cast aluminum alloys are frequently used as materials for cylinder head applications in internal combustion gasoline engines. These components must withstand severe cyclic mechanical and thermal loads throughout their lifetime. Reliable computational methods allow for accurate estimation of stresses, strains, and temperature fields and lead to more realistic Thermomechanical Fatigue (TMF) lifetime predictions. With accurate numerical methods, the components could be optimized via computer simulations and the number of required bench tests could be reduced significantly. These types of alloys are normally optimized for peak hardness from a quenched state that maximizes the strength of the material. However due to high temperature exposure, in service or under test conditions, the material would experience an over-ageing effect that leads to a significant reduction in the strength of the material.
Technical Paper

Tooling Effects on Edge Stretchability of AHSS in Mechanical Punching

2019-04-02
2019-01-1086
Edge stretchability reduction induced by mechanical trimming is a critical issue in advanced high strength steel applications. In this study, the tooling effects on the trimmed edge damage were evaluated by the specially designed in-plane hole expansion test with the consideration of three punch geometries (flat, conical, and rooftop), three cutting clearances (6%, 14%, and 20%) and two materials grades (DP980 and DP1180). Two distinct fracture initiation modes were identified with different testing configurations, and the occurrence of each fracture mode depends on the tooling configurations and materials grades. Digital Image Correlations (DIC) measurements indicate the materials are subject to different deformation modes and the various stress conditions, which result in different fracture initiation locations.
Technical Paper

Combustion-Timing Control of Low-Temperature Gasoline Combustion (LTGC) Engines by Using Double Direct-Injections to Control Kinetic Rates

2019-04-02
2019-01-1156
Low-temperature gasoline combustion (LTGC) engines can provide high efficiencies and extremely low NOx and particulate emissions, but controlling the combustion timing remains a challenge. This paper explores the potential of Partial Fuel Stratification (PFS) to provide fast control of CA50 in an LTGC engine. Two different compression ratios are used (CR=16:1 and 14:1) that provide high efficiencies and are compatible with mixed-mode SI-LTGC engines. The fuel used is a research grade E10 gasoline (RON 92, MON 85) representative of a regular-grade market gasoline found in the United States. The fuel was supplied with a gasoline-type direct injector (GDI) mounted centrally in the cylinder. To create the PFS, the GDI injector was pulsed twice each engine cycle. First, an injection early in the intake stroke delivered the majority of the fuel (70 - 80%), establishing the minimum equivalence ratio in the charge.
Technical Paper

Brake System Design for Dedicated BEV Architectures

2018-10-05
2018-01-1870
As fossil fuels dwindle and more electric vehicles enter the market, there is an opportunity to reevaluate the standard brake system. This paper will discuss and compare the differences in brake system sizing between a non-regenerative braking internal combustion engine vehicle and a dedicated battery electric vehicle with regenerative braking. It will use a model derived from component dynamometer testing and vehicle test data of a mid-size production vehicle. The model will be modified for the mass and regenerative braking capabilities of a battery electric vehicle. The contribution of regenerative braking energy will be analyzed and compared to show its impact on component sizing, thermal sizing, and lining life. The detailed design study will calculate the parameters for caliper, rotor design, actuation, etc., that are optimized for 100% regen enabled vehicles.
Technical Paper

Bowl Geometry Effects on Turbulent Flow Structure in a Direct Injection Diesel Engine

2018-09-10
2018-01-1794
Diesel piston bowl geometry can affect turbulent mixing and therefore it impacts heat-release rates, thermal efficiency, and soot emissions. The focus of this work is on the effects of bowl geometry and injection timing on turbulent flow structure. This computational study compares engine behavior with two pistons representing competing approaches to combustion chamber design: a conventional, re-entrant piston bowl and a stepped-lip piston bowl. Three-dimensional computational fluid dynamics (CFD) simulations are performed for a part-load, conventional diesel combustion operating point with a pilot-main injection strategy under non-combusting conditions. Two injection timings are simulated based on experimental findings: an injection timing for which the stepped-lip piston enables significant efficiency and emissions benefits, and an injection timing with diminished benefits compared to the conventional, re-entrant piston.
Technical Paper

The Development and Evaluation of Robust Combustion Systems for Miller Cycle Engines

2018-04-03
2018-01-1416
Miller Cycle engines employ a high expansion ratio to achieve high part-load efficiency, while minimizing knock sensitivity by using valve events that limit the effective compression ratio. The Miller effect may be achieved using either early or late intake valve closure. Combustion systems for these engines must be carefully designed to obtain adequate trapped charge to achieve full-load objectives as well as charge motion characteristics supporting good mixture preparation and flame propagation. This paper summarizes the results of a holistic project tasked with developing robust combustion systems for both early and late intake valve closure strategies. Based on best practices from conventional engines and preliminary Miller cycle requirements, a series of combustion systems was designed. These were analyzed using 3-dimensional computational fluid dynamics and those showing favorable combustion characteristics were experimentally evaluated using a modular single cylinder engine.
Technical Paper

Numerical Study of Twist Spring-back Control with an Unbalanced Post-stretching Approach for Advanced High Strength Steel

2018-04-03
2018-01-0806
Twist spring-back would interfere with stamping or assembling procedures for advanced high strength steel. A “homeopathic” resolution for controlling the twist spring-back is proposed using unbalanced post-stretching configuration. Finite element forming simulation is applied to evaluate and compare the performance for each set of unbalanced post-stretching setup. The post-stretching is effectuated by stake bead application. The beads are separated into multiple independent segments, the height and radii of which can be adjusted individually and asymmetrically. Simulation results indicate that the twist spring-back can be effectively controlled by reducing the post-stretching proximate to the asymmetric part area. Its mechanism is qualitatively revealed by stress analyses, that an additional but acceptable cross-sectional spring-back re-balances the sprung asymmetrical geometry to counter the twist effect.
Technical Paper

System Engineering for Automated Software Update of Automotive Electronics

2018-04-03
2018-01-0750
In traditional automotive electronic design, software update has been a component oriented, manual process rather than a systematic designed in capability suitable for automation. In recent days as software content in vehicles grow, the need to update software in vehicles more frequently is becoming a necessity. Moreover, additional attributes for software updates, for example timely delivery of security related update for vehicles, desire to add features using software update, control cost of software updates, etc., requires a system engineered design rather than a component oriented approach. As the automobile domain utilizes various means of mobility (Combustion Engine, Hybrid, Battery, etc.) and various functional domains (Infotainment, Safety, Mobility, Telematics, ADAS (Advance Driving Assist service), Autonomous, etc.), to control the overall cost of future software update for such a diverse environment, it is beneficial to introduce automation in the software update process.
Technical Paper

Initial Comparisons of Friction Stir Spot Welding and Self Piercing Riveting of Ultra-Thin Steel Sheet

2018-04-03
2018-01-1236
Due to the limitations on resistance spot welding of ultra-thin steel sheet (thicknesses below 0.5 mm) in high-volume automotive manufacturing, a comparison of friction stir spot welding and self-piercing riveting was performed to determine which process may be more amenable to enabling assembly of ultra-thin steel sheet. Statistical comparisons between mechanical properties of lap-shear tensile and T-peel were made in sheet thickness below 0.5 mm and for dissimilar thickness combinations. An evaluation of energy to fracture, fracture mechanisms, and joint consistency is presented.
Journal Article

Modeling Forming Limit in Low Stress Triaxiality and Predicting Stretching Failure in Draw Simulation by an Improved Ductile Failure Criterion

2018-04-03
2018-01-0801
A ductile failure criterion (DFC), which defines the stretching failure at localized necking (LN) and treats the critical damage as a function of strain path and initial sheet thickness, was proposed in a previous study. In this study, the DFC is revisited to extend the model to the low stress triaxiality domain and demonstrates on modeling forming limit curve (FLC) of TRIP 690. Then, the model is used to predict stretching failure in a finite element method (FEM) simulation on a TRIP 690 steel rectangular cup draw process at room temperature. Comparison shows that the results from this criterion match quite well with experimental observations.
Journal Article

Development of a Lightweight Third-Generation Advanced High-Strength Steel (3GAHSS) Vehicle Body Structure

2018-04-03
2018-01-1026
This article covers an application of third-generation advanced high-strength steel (3GAHSS) grades to vehicle lightweight body structure development. Design optimization of a vehicle body structure using a multi-scale material model is discussed. The steps in the design optimization and results are presented. Results show a 30% mass reduction potential over a baseline mid-size sedan body side structure with the use of 3GAHSS.
Journal Article

A Study of Piston Geometry Effects on Late-Stage Combustion in a Light-Duty Optical Diesel Engine Using Combustion Image Velocimetry

2018-04-03
2018-01-0230
In light-duty direct-injection (DI) diesel engines, combustion chamber geometry influences the complex interactions between swirl and squish flows, spray-wall interactions, as well as late-cycle mixing. Because of these interactions, piston bowl geometry significantly affects fuel efficiency and emissions behavior. However, due to lack of reliable in-cylinder measurements, the mechanisms responsible for piston-induced changes in engine behavior are not well understood. Non-intrusive, in situ optical measurement techniques are necessary to provide a deeper understanding of the piston geometry effect on in-cylinder processes and to assist in the development of predictive engine simulation models. This study compares two substantially different piston bowls with geometries representative of existing technology: a conventional re-entrant bowl and a stepped-lip bowl. Both pistons are tested in a single-cylinder optical diesel engine under identical boundary conditions.
Technical Paper

Experimental and Numerical Studies of Bowl Geometry Impacts on Thermal Efficiency in a Light-Duty Diesel Engine

2018-04-03
2018-01-0228
In light- and medium-duty diesel engines, piston bowl shape influences thermal efficiency, either due to changes in wall heat loss or to changes in the heat release rate. The relative contributions of these two factors are not clearly described in the literature. In this work, two production piston bowls are adapted for use in a single cylinder research engine: a conventional, re-entrant piston, and a stepped-lip piston. An injection timing sweep is performed at constant load with each piston, and heat release analyses provide information about thermal efficiency, wall heat loss, and the degree of constant volume combustion. Zero-dimensional thermodynamic simulations provide further insight and support for the experimental results. The effect of bowl geometry on wall heat loss depends on injection timing, but changes in wall heat loss cannot explain changes in efficiency.
Technical Paper

Spark Assist for CA50 Control and Improved Robustness in a Premixed LTGC Engine – Effects of Equivalence Ratio and Intake Boost

2018-04-03
2018-01-1252
Low-temperature gasoline combustion (LTGC) engines can deliver high efficiencies, with ultra-low emissions of nitrogen oxides (NOx) and particulate matter (PM). However, controlling the combustion timing and maintaining robust operation remains a challenge for LTGC engines. One promising technique to overcoming these challenges is spark assist (SA). In this work, well-controlled, fully premixed experiments are performed in a single-cylinder LTGC research engine at 1200 rpm using a cylinder head modified to accommodate a spark plug. Compression ratios (CR) of 16:1 and 14:1 were used during the experiments. Two different fuels were also tested, with properties representative of premium- and regular-grade market gasolines. SA was found to work well for both CRs and fuels. The equivalence ratio (ϕ) limits and the effect of intake-pressure boost on the ability of SA to compensate for a reduced Tin were studied. For the conditions studied, ϕ=0.42 was found to be most effective for SA.
Journal Article

Sizing Next Generation High Performance Brake Systems with Copper Free Linings

2017-09-17
2017-01-2532
The high performance brake systems of today are usually in a delicate balance - walking the fine line between being overpowered by some of the most potent powertrains, some of the grippiest tires, and some of the most demanding race tracks that the automotive world has ever seen - and saddling the vehicle with excess kilograms of unsprung mass with oversized brakes, forcing significant compromises in drivability with oversized tires and wheels. Brake system design for high performance vehicles has often relied on a very deep understanding of friction material performance (friction, wear, and compressibility) in race track conditions, with sufficient knowledge to enable this razor’s edge design.
Technical Paper

Integrated Computational Materials Engineering (ICME) Multi-Scale Model Development for Advanced High Strength Steels

2017-03-28
2017-01-0226
This paper presents development of a multi-scale material model for a 980 MPa grade transformation induced plasticity (TRIP) steel, subject to a two-step quenching and partitioning heat treatment (QP980), based on integrated computational materials engineering principles (ICME Model). The model combines micro-scale material properties defined by the crystal plasticity theory with the macro-scale mechanical properties, such as flow curves under different loading paths. For an initial microstructure the flow curves of each of the constituent phases (ferrite, austenite, martensite) are computed based on the crystal plasticity theory and the crystal orientation distribution function. Phase properties are then used as an input to a state variable model that computes macro-scale flow curves while accounting for hardening caused by austenite transformation into martensite under different straining paths.
Technical Paper

Latest Advances in Aluminum Shape Casting

2017-03-28
2017-01-1665
With the increasing use of aluminum shape castings in structural applications in automobiles, assurance of cast product integrity and performance has become critical in both design and manufacturing. In this paper, the latest understanding of the relationship between casting quality and mechanical properties of aluminum castings is summarized. Examples of newly developed technologies for alloy design, melting and melt treatment, casting and heat treatment processes in aluminum casting are reviewed. Robust design and development of high integrity aluminum castings through an Integrated Computational Materials Engineering (ICME) approach is also discussed.
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