Data Driven Model to Predict Cylinder Head Fatigue Failure

<div class="htmlview paragraph">Various investigators<sup>(<span class="xref">1</span>)</sup> have recognized that difficulties exist in obtaining octane ratings in the standardized single-cylinder laboratory CFR engine above 100 O.N. Efforts are being made by cooperative groups (such as ASTM) and individual laboratories to solve some of the problems. In the meantime, at the Sun Automotive laboratory, these developments have been paralleled by looking at the road rating problems using some “future design” experimental engines at a nominal 12:1 C.R. level. These engines were 1956 production engines of three different types modified to represent the high compression engine of a few years hence. The modified engines were installed in 1956 production cars.</div> <div class="htmlview paragraph">Recognizing that the ability of a petroleum refinery laboratory group to anticipate future engine design features is subject to some criticism, it was still felt that the results might well be helpful in defining future problems. Actually previous experience has been encouraging along this line in that results obtained from engines modified to 10:1 C.R. in1954 have been substantiated closely by 10:1 C.R. 1957 production cars.</div> <div class="htmlview paragraph">Questions have been raised as to whether cars at the 12:1 C.R. level will be knock-limited or whether other abnormal combustion phenomena such as surface ignition, rumble, etc., will confuse the knocking reaction. Experience at the Sun laboratory has led to the feeling that surface ignition and/or rumble can be a limiting factor at this level, depending on how deposits are accumulated. However, the three 12:1 C.R. cars used were all knock-limited under the suburban driving build-up procedure employed. Using a fuel-oil combination typical of commercial products anticipated for the next few years, there were no evidences of surface ignition or rumble either during the nominal 5000-mile build-up period or during the rating period.</div> <div class="htmlview paragraph">While the limited amount of work to date does not justify drawing firm conclusions, results have indicated that: <ol class="list nostyle"> <li class="list-item"> <span class="li-label">(a)</span> <div class="htmlview paragraph">Fuels up to about 105 Research O.N. (or about 110 O.N. road rating) can be rated satisfactorily in 12:1 C.R. cars using either Modified Uniontown or Modified Borderline procedures.</div></li> <li class="list-item"> <span class="li-label">(b)</span> <div class="htmlview paragraph">Reproducibility of road rating results on fuels in the 100 to 105 Research O.N. range is comparatively good; about as good as on fuels below 100 O.N.</div></li> <li class="list-item"> <span class="li-label">(c)</span> <div class="htmlview paragraph">Relationships can be established between road and laboratory ratings which either compare with or extend previous correlations in the 90 to 100 O.N. bracket.</div></li> <li class="list-item"> <span class="li-label">(d)</span> <div class="htmlview paragraph">The clarity of the knock, time consumed per rating, and individual operator's ability to rate are all about equal to those in the area below 100 O.N.</div></li></ol></div> <div class="htmlview paragraph">So much for the over-all relationships observed. The remainder of the paper will discuss in some detail the approach used and some of the more interesting fuel-engine relationships found.</div>

<div class="section abstract"><div class="htmlview paragraph">The paper presents a numerical activity directed at the analysis and optimization of internal combustion engine water cooling jackets, with particular emphasis on the fatigue-strength assessment and improvement.</div><div class="htmlview paragraph">In the paper, full 3D-CFD and FEM analyses of conjugate heat transfer and load cycle under actual engine operation of a single bank of a current production V6 turbocharged diesel engine are reported.</div><div class="htmlview paragraph">A highly detailed model of the engine, made up of both the coolant galleries and the surrounding metal components, i.e., the engine head, the engine block, the gasket, the valve guides and valve seats, is used on both sides of the simulation process to accurately capture the influence of the cooling system layout under thermal and load conditions as close as possible to actual engine operations.</div><div class="htmlview paragraph">Concerning the CFD side, a 50-50 binary mixture of ethylene-glycol and water is used in order to correctly reproduce the coolant behavior, while boundary conditions are derived from a combination of experimental measurements and a CFD-1D model of the whole engine.</div><div class="htmlview paragraph">In order to find a proper CFD setup for the optimization of the thermal behavior of the engine, a preliminary comparison between experimental temperature distribution within the engine head and CFD forecasts is carried out. Eight thermocouples are used to measure the engine head local temperature at some critical locations.</div><div class="htmlview paragraph">Among the many competing numerical sub-models involved in the CFD simulations, particular attention is devoted to the modeling of phase transition and vapor nuclei formation within the coolant galleries.</div><div class="htmlview paragraph">Concerning the FEM side, thermo-mechanical analyses are carried out aiming at addressing the design optimization of the engine in terms of fatigue strength. In view of the wide range of thermal and load conditions, both high-cycle and low-cycle fatigue must be properly characterized by means of ad-hoc criteria. An energy-based criterion specifically suited for low-cycle fatigue regions is therefore superimposed to well-established S-N o ε-N criteria for the high cycle fatigue regions.</div><div class="htmlview paragraph">The proposed methodology shows very promising results in terms of point-wise detection of possible engine failures and proves to be an effective tool for the accurate thermo-mechanical characterization of internal combustion engines under actual life-cycle operations.</div></div>

<div class="htmlview paragraph">Brake noise dynamometers are fundamental engineering tools for the systematic and efficient investigations of noise. However, the data obtained from a dynamometer must correlate with the noise achievable on a corresponding vehicle to be of true value in an investigation.</div> <div class="htmlview paragraph">The factors that can influence correlation between both vehicle and dynamometer tests are examined. In particular, correlation based on the following: <ul class="list disc"> <li class="list-item"> <div class="htmlview paragraph">techniques for noise data acquisition, evaluation and testing</div> </li> <li class="list-item"><div class="htmlview paragraph">variations of the brake system under load and time such as aging and wear effects</div> </li> <li class="list-item"><div class="htmlview paragraph">differences in the test procedure brake application parameters</div> </li> <li class="list-item"><div class="htmlview paragraph">variability of individual brake system components in terms of technical release and part-to-part variation.</div> </li> </ul> </div> <div class="htmlview paragraph">Problems and approaches for correlating dynamometer and vehicle brake test results are described. Test results for the correlation dynamometer - vehicle are also shown.</div>

<div class="section abstract"><div class="htmlview paragraph">There is a demonstrated need for effective design verification testing to support certification strategies for nascent electric motors and electric propulsion systems. Design efforts pursue efficiency pushing electrified propulsion rotors to be lighter and incorporate greater power density; however, there is no clear path established for supporting structural integrity and durability test requirements as required by global certification agencies.</div><div class="htmlview paragraph">Application of new materials, unique rotor design characteristics, and modified certification requirements drive unusual requirements for rotor modeling substantiated by component test data that addresses complex stress distribution characteristics.</div><div class="htmlview paragraph">Our paper addresses testing electrified propulsion rotors using spin test protocols adapted to support integrity and durability test goals. We further incorporate key concerns for planning and executing component spin tests of rotating structures necessary to support global engine certification efforts. Results from component tests are effective for mitigating risks associated with the preservation of certification test schedules and potential end product safety issues.</div><div class="htmlview paragraph">This paper presents data measurement techniques that are incorporated with specific spin tests to enhance the value of acquired data. Adapted test protocols include Overspeed and Low cycle fatigue (LCF) tests, which are more relevant types of spin tests for certification purposes.</div><div class="htmlview paragraph">Innovative measurement techniques for capturing the rotor growth behavior for both mappings the speed-dependent growth trends and the circumferential profile of deforming rotor under centrifugal load generate useful data to evaluate materials and structural behavior affecting performance up to failure.</div></div>

<div class="htmlview paragraph">The next major aircraft program currently entering the study phase is to be a multi-mission fighter which would compliment the ATF and replace the F-16. The initial operational capability (IOC) of this aircraft will enable it to benefit from the propulsion technology advances of the Integrated High Performance Engine Technology (IHPTET) initiative. Past studies have shown that in order to achieve the optimum performance from these new advanced cores the engine cycle (specifically the fan pressure ratio) must be tailored to the aircraft mission and performance requirements.</div> <div class="htmlview paragraph">The missions and requirements to define this advanced fighter are currently in the embryonic stage. Even though the requirements are undefined, the engine company can evaluate a matrix of engine cycles in a notional airframe over a range of mission and performance levels. This effort can provide insight into the range of advanced engine cycles that might be required to optimize the future weapon system. This assessment can also provide a database to aid future aircraft designers, engine designers, and survivability analysts in their studies to recommend more specific requirements for this advanced multi-mission fighter.</div> <div class="htmlview paragraph">The focus of this paper is twofold. First, to present an approach which is used to generate a database of engine cycle/size as functions of mission definition and performance requirements. And second, to demonstrate how the aircraft mission and performance requirements impact the engine cycle and size. Specifically, a series of IHPTET class, Phase II, preliminary study engine cycles at four different fan pressure ratio (FPR) will be assessed in a notional advanced fighter performing four missions and at varied levels of performance requirements.</div>

<div class="htmlview paragraph">The problem of cracks in cylinder heads due to low cycle fatigue (thermal fatigue) is well known for engines with high specific power output. However it is still difficult to predict the lifetime of a new cylinder head due to the number of influencing parameters and the complexity of material behavior. Better understanding of cylinder head fatigue can improve the development process of a new engine concerning CAE as well as mechanical testing efficiency.</div> <div class="htmlview paragraph">Therefore a CAE tool which can calculate strains and stresses as a function of time for a defined operating cycle of the engine was developed. In parallel a measuring technique was developed which allows to measure strains on the surface of the combustion chamber side of the cylinder head during fired engine operation.</div> <div class="htmlview paragraph">For different Aluminum-Silicon casting alloys the material behavior was described in the Finite Element Program ABAQUS by a nonlinear kinematic / isotropic hardening model. The numerical parameters were determined by measurement results. The cyclic thermal load (55°C - 210°C.) was applied to the assembled cylinder head FE-model.</div> <div class="htmlview paragraph">A strain gage application was developed which allows dynamic strain and surface temperature measurements during fired engine operation. The results are used for comparison to and calibration of the calculations. More-over they can serve to optimize thermo-shock-test cycles. The measured time behavior of the material strains makes it possible to optimize the hot and cold cycle duration of thermo-shock tests regarding complete test duration and lifetime validity.</div> <div class="htmlview paragraph">In this paper, the potential for improving of the numerical model is discussed and the successful use of conventional strain gages during fired engine operation is described. A comparison of calculated and measured strain in a temperature cycle validates the results.</div>

<div class="section abstract"><div class="htmlview paragraph">This paper discusses the optimization of an automotive hydraulic steering pump pulley design for improved in-vehicle pump NVH performance. Levels of steering pump whine noise heard inside a vehicle were deemed objectionable. Vehicle and component transfer path analyses indicated that the dominant noise path for the whine noise was airborne in nature. Subsequent experimental modal analysis indicated that the steering pump pulley was a major contributor to the amount of radiated noise produced by the pump/pulley system. CAE analysis was used to further analyze the dynamic behavior of the pulley and develop an optimized design with decreased noise radiation efficiency. The results predicted with the CAE analysis were verified in-vehicle, resulting in a vehicle with acceptable steering pump whine noise performance.</div></div>

<div class="section abstract"><div class="htmlview paragraph">Modern project management including brake testing includes the exchange of reliable results from different sources and different locations. The ISO TC22/SWG2-Brake Lining Committee established a task force led by Ford Motor Co. to determine and analyze root causes for variability during dynamometer brake performance testing. The overall goal was to provide guidelines on how to reduce variability and how to improve correlation between dynamometer and vehicle test results. This collaborative accuracy study used the ISO 26867 Friction behavior assessment for automotive brake systems. Future efforts of the ISO task force will address NVH and vehicle-level tests.</div><div class="htmlview paragraph">This paper corresponds to the first two phases of the project regarding performance brake dynamometer testing and presents results, findings and conclusions regarding repeatability (within-lab) and reproducibility (between-labs) from different laboratories and different brake dynamometers. The new EKB 3008 data exchange format was used by participating facilities to share test results using spreadsheet applications, help automate the evaluations, and simplify the different comparisons performed for this project. This on one of the first practical applications for the EKB 3008 format with several software platforms involved.</div><div class="htmlview paragraph">In order to minimize variations caused by test parts, components (brake discs, brake pads, calipers and vehicle knuckles) were carefully selected, prepared, and measured prior to testing. Special attention was given to: test procedure implementation, critical braking and testing conditions, dynamometer setup and controls, data collection, data processing and test evaluation routines. Statistical analysis (Minitab® and ISO Statistical Methods) were used to separate variability caused by test parts and caused by the test setup. Based on the findings, the paper presents guidelines for improving repeatability (within-lab) and reproducibility (between-labs) during regular testing activities.</div><div class="htmlview paragraph">Compared to vehicle testing, variability root-cause investigation using brake dynamometers is more efficient (less sources of variation and less use of testing and engineering resources) and under more controlled conditions. Findings from this variability study will support future improvement efforts for several laboratory and vehicle performance and NVH test procedure and techniques.</div></div>

<div class="htmlview paragraph">The effect of external EGR on knock was evaluated using a CFR engine. Combustion pressure was sampled on a time basis. A band pass filter in the time domain was applied to the pressure cycles. Five knock indices were calculated for each combustion cycle.</div> <div class="htmlview paragraph">The problem to quantify knock intensity was focused. At this extent measurements were carried out on standard isooctane-n-heptane blends in the test conditions used for the determination of the Motor Method Octane Number (MON). Knock intensity was varied acting on compression ratio.</div> <div class="htmlview paragraph">For each index, the conditions of absence of knock were determined using motored cycles. The indices were compared and one of them, showing the lowest C.O.V., was selected for further measurements.</div> <div class="htmlview paragraph">The effect of EGR on test fuels having different composition was evaluated varying the compression ratio, at fixed ignition timing. In this way, the same level of detonation, obtained in the absence of EGR, was realized with different amount of external EGR. Percent variation of compression ratio was used to compare the ability of fuels, having different octane number, to tolerate compression ratio increase in presence of EGR.</div> <div class="htmlview paragraph">In particular the tests were carried out on a matrix of twelve fuels with three levels of EGR. The result show that with all tested fuels the percent increase of compression ratio is strongly dependent on EGR.</div>

<div class="htmlview paragraph">This paper describes work being conducted by OC Robotics and Airbus to develop snake-arm robots to conduct assembly tasks within wing boxes - an area currently inaccessible for automation.</div> <div class="htmlview paragraph">The composite, single skin construction of aircraft structures presents new assembly challenges. Currently during box close-out it is necessary for aircraft fitters to climb into the wing box through small access panels and use manual or power tools to perform a variety of tasks. In future wing designs it may be that certain parts of the wing do not provide adequate access for manual assembly methods. It is also known that these manual interventions introduce health and safety concerns with their associated costs.</div> <div class="htmlview paragraph">Snake-arm robots provide a means to replace manual procedures by delivering the required tools to all areas of the wing box.</div> <div class="htmlview paragraph">Such a development has broader implications for aircraft design and assembly. There is potential for considerable cost savings for the aerospace industry through reduced weight, improved aerodynamics, standardisation of assembly processes, increased rate and reduced health and safety costs.</div> <div class="htmlview paragraph">This paper presents early results of the demonstration snake-arm robot and outlines expectations for future development. It also identifies critical design parameters for the snake-arm and considers the tools and processes delivered by the snake-arm.</div>

<div class="section abstract"><div class="htmlview paragraph">The Indian automotive industry has migrated from BS IV (Bharat stage IV) to BS VI (Bharat Stage VI) emission norms from 1<sup>st</sup> April 2020. This two-step migration of the emission regulations from BS IV to BS VI demands significant engineering efforts to design and integrate highly complex exhaust after-treatment system (EATS). In the present work, the methodology used to evaluate the EATS of a high power-density 1.5-liter diesel engine is discussed in detail. The EATS assembly of the engine consists of a diesel oxidation catalyst (DOC), a diesel particulate filter with selective catalytic reduction coating (sDPF), urea dosing module and urea mixer. Typically, all these components that are needed for emission control are integrated into a single canning of shell thickness ~1.5mm. Moreover, the complete EATS is directly mounted onto the engine with suitable mounting brackets on the cylinder block and cylinder head. The mounting brackets of the after-treatment system should be stiff enough to withstand the high cycle fatigue vibration loads coming from the engine. On the other hand, the brackets should allow the system to expand freely under high temperatures to avoid any low cycle fatigue issues created due to thermal loads at 800 deg.C. Hence, a robust methodology is followed to ensure the robustness of the entire system. The methodology included the prediction of metal temperature using a conjugate heat transfer analysis, high-temperature modal analysis, stress-strain analysis and high-cycle vibration fatigue analysis. In order to evaluate the system from the thermal compliance point of view, a high-temperature stress-strain analysis is carried out in a thermal shock test cycle. The simulation results have shown that the brackets positioned at the near-zero thermal expansion zone could have a much lesser plastic strain due to reduced thermal stress. Taking advantage of this, the stiffness of the brackets could be increased to improve the modal frequency values and robustness against high-cycle vibration fatigue. The paper gives a detailed insight on optimizing the bracket design of the EATS to ensure that a robust design solution is finalized.</div></div>

<div class="htmlview paragraph">Effective control of lube oil contaminants is rapidly becoming of critical concern to diesel engine manufacturers. The key force creating this concern is engine design changes resulting from more restrictive diesel emissions regulations. As a result of these changes, more contaminants from combustion as well as those from component wear are being retained in the crankcase, severely challenging oil additive and engine durability.</div> <div class="htmlview paragraph">In this study, two identical 2.0 liter direct-injection turbocharged diesel engines were repetitively loaded through a 120 minute maximum-torque, maximum-power, maximum-speed cycle, and wear was accelerated by a forced injection of Air Cleaner Fine Test Dust (AC Spark Plug Division, GMC) into the lubrication circuit.</div> <div class="htmlview paragraph">The baseline design engine used the standard factory-equipped lube filter while the other was equipped with a block-mounted bypass oil cleaning centrifuge in addition to the standard full-flow filter. Online data-acquisition equipment monitored wear-related performance characteristics. After-test measurements compared total wear and surface profiles on seven engine components over the 150 hour test.</div> <div class="htmlview paragraph">Test results showed dramatic reductions in piston ring blow-by and component wear through application of the centrifuge oil cleaner. At test end, blow-by on the uncontrolled baseline engine was 140% higher than on the test engine equipped with the centrifuge. In addition, piston ring weight loss was 90% less than that experienced with the baseline engine filter system. In this report, the engine accelerated wear test results are complemented with a summary of North American field experience from major heavy-duty line-haul truck fleet users of the oil cleaning centrifuge.</div>

<div class="htmlview paragraph">The development of a successful fuel additive requires considerable effort, a large share of which must be expended on the effect of the additive on engine durability. Durability may be affected as soon as the fuel enters the fuel tank and the possibility of such good or bad effects continues until the exhaust gases have cleared the rear bumper. Some of the durability aspects which can be either improved or made more severe are listed, these include fuel system corrosion, carburetor and manifold deposits, combustion chamber and spark plug deposits, engine wear and general cleanliness and bearing, exhaust system and rear bumper corrosion.</div> <div class="htmlview paragraph">It is shown that of seven experimental additives tested in a fleet of passenger cars of one make operated under severe duty conditions, four additives decreased exhaust valve life while three increased exhaust valve life by from twenty-five to fifty per cent. In another make of passenger car operated under the same severe conditions, none of the additives affected valve life. It is also shown that as little as one gallon of additive in 50,000 gallons of fuel may reduce exhaust valve life to half of normal. Increased amounts of the same additive may actually increase exhaust valve life by more than half.</div> <div class="htmlview paragraph">Consideration of all of these factors make it necessary to conduct thousands of hours of dynamometer tests and millions of miles of road tests in a wide variety of engines before a fuel additive can be marketed with assurance that its over-all effects will benefit the ultimate user. The philosophy of durability testing, choice of test equipment and actual test schedules used by Ethyl Corporation in their durability tests are discussed.</div>

<div class="htmlview paragraph">In recent years, small diesel engines for industrial use are required to achieve still higher power output per engine size (high power density) and to have the performance to comply with stringent exhaust emissions standards as well. To meet these social demands and market requirements, there are various engineering tasks yet to accomplish. In this paper, two important technical issues have been focused, those are, combustion system improvement to enable lower exhaust emissions and higher power output than conventional models and new cooling system as a solution for increased heat load issue accompanying the progress of high power density.</div> <div class="htmlview paragraph">Firstly, for combustion system improvement, the swirl adjustment technique has been developed that will optimize the swirl ratio for each engine application with different load and speed condition. Intake airflow has been analyzed using Computational Fluid Dynamics (CFD) approach to enable adjustment of swirl ratio that plays an important role in creating air fuel mixture. The swirl was successfully controlled by providing the originally designed configuration on the wall, from cylinder block side, which introduces the intake air from valve throat area into cylinder. As a result, it is now possible to set optimum swirl ratio for each engine application while securing high volumetric efficiency.</div> <div class="htmlview paragraph">Next, a new cooling system has been introduced to cool down the neighborhood of top deck between cylinders where temperature becomes highest in cylinder block. The new coolant channels with built-in multiple water passages was incorporated by casting between cylinders. As a result, the temperatures between cylinders and in piston ring groove could be lowered remarkably.</div> <div class="htmlview paragraph">After overcoming these engineering challenges, the advanced high power density has successfully been materialized in small direct injection (DI) diesel engine for industrial use.</div>

<div class="htmlview paragraph">Low-cycle fatigue is a term used to describe the thermal and/or mechanical loading conditions which cause premature failure of materials at less than 20,000 cycles. These cyclic stress conditions are prevalent during engine start-up or shut down and in severe flight maneuvers. From the design standpoint, it is important to assess and predict the behavior of compressor and turbine component materials under these severe conditions.</div> <div class="htmlview paragraph">This paper presents the low cycle fatigue data on six candidate materials which were considered for an advanced engine. The materials were investigated simultaneously by pull-pull and by modified rotating beam fatigue testing techniques. Results indicate that the candidate materials can sustain appreciable cycling at stress levels beyond design limit before fracture occurs by the low cycle fatigue mechanism. Of the materials investigated, Udimet 630 exhibited the optimum low cycle fatigue resistance.</div>