bluuebunny/crossref_metadata_2025 huggingface dataset:
Wear mechanisms of sandwich-type video heads
Authors: Harrison M J K , Sullivan J L , Theunissen G S A M
Published: October 2002

Differential wear between the various material components of composite magnetic recording heads is observed upon running against the magnetic medium. A developing level difference between the magnetic material and the medium bearing surface leads to signal degradation, exponential with the difference and the signal frequency. Experimental evidence is presented for a three-body erosion mechanism in the case of sandwich heads employed in commercial helical scan, Hi-8 video tape recorders. Two sintered ceramic substrates, CaTiO3 and composite Zr-doped CaTiO3, in combination with three soft magnetic materials, amorphous CoNbZr and the nanocrystalline iron alloys FeNbSiN and FeTaN, have been studied. They have been studied in conjunction with commercial metal evaporated (ME) and metal particulate (MP) tapes. Level difference has been measured by interferometry and AFM (atomic force microscopy), the latter also observing level differences between the various components of the sandwich: soft magnetic metal, ceramic laminations and the metallic bonding layer. AFM shows a pull-out of particles from the ceramic substrate with similar sized particles observed on the track. Scanning Auger micrographs have shown the transfer of ceramic particles on to the track and of metal on to the substrate. Wear rates and wear mechanisms have been identified for the materials in isolation by studying single-material dummy heads. This has been identified as plastic deformation controlled microabrasion, transforming to grain pull-out in the crystalline materials in some instances. It is speculated that these pull-outs are responsible for the wear of the soft metallic track when this is out of contact with the tape. The evidence for chemical wear is inconclusive. The involvement of transfer material from the tape to the head is speculated upon.
Microtribological properties of hard amorphous carbon protective coatings for thin-film magnetic disks and heads
Authors: Koinkar V N , Bhushan B
Published: October 2002

For long durability of magnetic media and head sliders, protective overcoats of hydrogenated amorphous carbon (a-C:H) are generally used. In this study, microtribological studies of hydrogenated amorphous carbon coatings deposited on a single-crystal silicon using three different deposition techniques—sputtering, ion beam and cathodic arc—were studied using atomic force/friction force microscopy (AFM/FFM). Roughnesses of all coatings at two scan sizes of 1 μm × 1 μm and 10 μm × 10 μm are comparable. Surface topography of sputtered carbon coating shows some particulates on the surface. Cathodic arc carbon coating exhibits the lowest coefficient of friction value followed by ion beam and sputtered carbon coatings. Microscratch and wear resistance and nanohardness of cathodic arc carbon coating are superior to those of ion beam and sputtered carbon coatings. Cathodic arc deposited carbon coatings are potential candidates for magnetic disks and heads.
Stability analysis of a rigid rotor supported on hydrodynamic journal bearings with rough surfaces using the stochastic finite element method
Authors: Turaga R , Sekhar A. S. , Majumdar B. C.
Published: October 2002

The effect of surface roughness on the stability characteristics of hydrodynamic journal bearings has been studied. Roughness has been considered to be a stochastic variable, which is stationary, ergodic with mean zero. Both one-dimensional roughness (longitudinal and transverse) and two-dimensional roughness (isotropic) have been studied using the stochastic finite element method. Journal bearings with different width-diameter ratios have also been considered. It is seen that the transverse roughness tends to increase the stability (non-dimensional mass parameter) whereas in the case of isotropic roughness there is a decrease when compared with the smooth bearing. Longitudinal roughness has a marginal effect of decreasing the stability of hydrodynamic journal bearings with rough surfaces.
Stiffness and damping coefficients of air rings with a chamber feeding system
Authors: Czolczyñski K , Kapitaniak T , Marynowski K
Published: October 2002

When, during the operation of rotors supported in gas bearings, their rotational velocity reaches a sufficiently high value, loss of steady state stability occurs. This instability is caused by the loss of damping properties of the gas film, which leads to self-excited vibrations. These vibrations are the basic obstacle to a widespread application of gas bearings. The phenomenon of self-excited vibrations can be avoided by introducing an elastic supporting structure between the bearing bushes and the casing, characterized by properly selected stiffness and damping coefficients. In practice, such a structure can have the form of an externally pressurized gas ring.

In this paper, on the basis of selected examples, those ranges of the values of stiffness and damping coefficients of the gas ring that make it possible to retain steady state stability at practically any rotational velocity of the rotor are demonstrated. A design of the ring structure, especially of its feeding system, is also shown, which ensures the required values of stiffness and damping coefficients (with regard to the stability). These investigations have been carried out by means of a numerical simulation method with the use of a mathematical model of the gas bearing, which has already been verified many times.
Surface roughness modification in elastohydrodynamic line contacts operating in the elastic piezoviscous regime
Authors: Hooke C. J.
Published: October 2002

In heavily loaded elastohydrodynamic (EHD) lubrication contacts operating in the piezoviscous regime, the original surface roughness is largely flattened as it enters the conjunction and is replaced by an inlet generated clearance variation. This clearance variation is convected through the contact at the entrainment velocity. It has a spatial distribution that differs (except for rolling without slip) from the original surface and a different amplitude. This amplitude may be smaller or greater than that of the original profile.

An analytical solution of this behaviour is presented for contacts operating well inside the elastic piezoviscous regime for the situation where the roughness is relatively small compared with the film thickness. This solution allows the main features of surface roughness modification to be understood and produces results that compare well with the few numerical solutions available.
Performance study of a back-depression mechanical dry gas seal
Authors: Stolarski T. A. , Xue Y
Published: October 2002

An aerostatic mechanical dry gas seal is described in this paper. The seal has shallow depression grooves (compensators) on the back and annular grooves on one of the working faces. With the help of the back depression grooves, a hydrostatic pressure and thereby a separating force with satisfactory stiffness are produced within the sealing gap.

A model which takes surface roughness into account was used to predict the performance of the seal. Relationships between the control parameters (the recess position, rG, the nominal film thickness, h0, the depth, hv, of depression grooves and the surface roughness parameter, a) are investigated against various pressure ratios, pe/ pi. The analysis provides a simple optimum design procedure.

A finite element analysis was carried out to account for the effect of face deformation during operation of the seal. Experiments for various speeds, pressures and roughness parameters were carried out and the results from the experiments were used to validate the analysis performed. Analysis and experiment revealed the importance of the surface roughness and deformation of the faces for the creation and retention of the gap.
The contribution of erosive wear to the performance degradation of sliding spool servovalves
Authors: Vaughan N. D. , Pomeroy P. E. , Tilley D. G.
Published: October 2002

Flow conditions for sliding spool valves around their central position may be critical in terms of the resulting system performance. In-service changes that occur can cause a degradation of the performance of both the valve and the controlled system. The degradation due to erosive wear arising from solid particle contamination in the fluid flow is examined in detail in this paper. It reports the details of a test rig and methodology that has been carefully established to examine the effect of various factors on erosion wear. These factors include the contaminant particle size and concentration, differential pressure across the metering land, spool opening, spool surface hardness and flow direction, as well as fluid characteristics.
Unbalance response and stability analysis of a rotor supported on hydrodynamic journal bearings with rough surfaces
Authors: Turaga R , Sekhar A. S. , Majumdar B. C.
Published: October 2002

In this investigation the unbalance response and stability of a flexible rotor supported on hydrodynamic journal bearings with rough surfaces have been studied. The influence of the surface roughness patterns on the unbalance response and the stability of a rotor have been evaluated.
The inclusion of lubricant shear thinning in the short bearing approximation
Authors: Taylor R. I.
Published: October 2002

For short journal bearings (defined as those where L/D < 0.5, where L is the length and D is the diameter), such as those used in modern automotive engines, the 'short bearing approximation' is an attractive fast tool for bearing designers to use as a first approximation. The essence of the approximation is that the pressure variation across the width of the bearing is much greater than that around the circumference of the bearing. With this approximation, it is possible to neglect certain terms in the Reynolds equation, and an analytical expression for the pressure variation around the bearing can be written down. By integrating the pressure around the bearing, an analytical expression relating the load, W, to the eccentricity ratio, ε, may be obtained. The standard ‘short bearing approximation’ assumes that the lubricant is Newtonian, and so any variation in the lubricant viscosity with the shear rate is neglected.

In this paper, an isothermal analysis is made which uses the short bearing approximation but allows for the possibility of lubricant shear thinning. The variation in the lubricant viscosity with the shear rate is assumed to be as described by the Cross equation, which has previously been shown to give a good fit to measured flow curves. A detailed description of the analysis is given, together with results obtained when the model was applied to a modern automotive con-rod bearing. (Note that the effects of pressure on lubricant viscosity have been neglected.)
Elastohydrodynamic lubrication of rough surfaces
Authors: Lubrecht A. A. , Venner C. H.
Published: October 2002

The detailed understanding of elastohydrodynamic lubrication (EHL) with rough surfaces has become an important problem as the ratio of film thickness to surface roughness is decreasing. Recently it has been recognized that the roughness inside an EHL contact might be different from the roughness outside the contact owing to elastic deformation. As will be explained in this paper, a first step in understanding the deformation of a real rough surface is the detailed knowledge of the amplitude reduction of harmonic features, which forms the topic of this paper. For the line contact problem it is shown that the deformed amplitude of a harmonic feature (waviness) depends on the original amplitude of the feature, its wavelength and the contact operating conditions, including the slide-roll ratio. The amplitude reduction can be completely described by a single dimensionless parameter. For the point contact problem it is shown that the deformed amplitude of isotropic waviness depends on the original amplitude of the feature, its wavelength and the contact operating conditions. Once again, the amplitude reduction can be completely described by a single dimensionless parameter. The presented relations for line and circular contact can be used as a basis for a modified Λ parameter predicting the relation between the real ratio of film thickness to amplitude inside the EHL contact. A numerical example of the calculation of the deformation is given.
Elastohydrodynamic lubrication: A lubricant industry perspective
Authors: Bovington C
Published: October 2002

The twin challenges facing the automotive and lubricants industries as we approach the millennium are: how to reduce the levels of gaseous emissions and how to achieve increased durability. Improved durability is necessary in order to maintain low levels of emissions. The lubricant has an important part to play in both the improvement in durability by way of improved wear and in the reduction of emissions and conservation of non-renewable energy resources by way of the reduction of friction levels in engines.

Examples are shown of how the application of electrohydrodynamic lubrication (EHL) equations permit the calculation of the oil film distribution between cam and follower contacts as a function of cam angle, cam speed and oil viscosity. The results are compared to post-engine test cam wear patterns. The position with of maximum wear can thus be predicted and critical operating conditions identified.

The development of optical methods for studying EHL behaviour and simple, reliable, methods for measuring traction under EHL conditions represents a major advance and allows the development of lubricants that offer high levels of wear protection together with high levels of fuel efficiency. This paper shows the importance of selection of both base oils and additive packages to achieve these ends. The relationships between ambient pressure viscosity, pressure coefficient of viscosity, EHL film thicknesses and EHL traction coefficients are discussed. The use of such data in the prediction of fuel economy performance in industry engine tests is also discussed.
Computer prediction of mechanical seal performance and experimental validation
Authors: Zhu G
Published: October 2002

Correct prediction of the mechanical seal performance is essential to reduce the time and cost of new product development. For many years the knowledge gained from tribology research has laid a sound foundation for seal performance prediction. As a result of long-term commitment by John Crane EMA, a personal computer based software CSTEDYSM has been developed and continuously refined and validated since 1992. The recent development of the computer model through experimental investigation and extensive experimental validation has confirmed the accuracy and reliability of the model. This gives confidence in application of the software to mechanical seal design and performance optimization, special product application and trouble shooting. It is estimated that a new product development period can be cut significantly due to the implementation of this software.
Limiting speeds and operating temperatures of fixed preload large bore angular contact ball bearings for machine tools
Authors: Lacey S. J. , Kemble A
Published: October 2002

Because of the ability of angular contact ball bearings to support both radial and axial loads and operate at high speeds, they are used widely to support machine tool spindles. The limiting speed of angular contact bearings depends on a number of factors including the type of bearing arrangement, preload, lubrication and bearing spacing. Preloaded back-to-back angular contact ball bearings are commonly used and in this paper the limiting speed of such an arrangement is considered together with a simple method for estimating speed factors which is shown to agree with actual experience.

Also, little information is available on the operating temperatures of large angular contact bearings and so the effect of lubrication conditions on the limiting speed of angular contact bearings of 200 mm bore are investigated. In particular the design of the lubrication nozzle is shown to have a significant influence on the bearing operating temperature.
Design and selection of mechanical seals to minimize emissions
Authors: Bowden P. E.
Published: October 2002

The design of mechanical seals for applications requiring the control of fugitive emissions is reviewed. The paper discusses the features inherent in seal design and how these affect overall performance; it also examines the effect of materials of construction. Selection guidelines comparing various mechanical seal arrangements are included, these being based on operational experience in working plants. Significant events in the development of emission regulations and therefore modern sealing solutions are described.
Torsional vibration of a back-to-back gearbox rig Part 2: Time domain modelling and verification
Authors: Leishman B A , Drew S J , Stone B J
Published: October 2002

The torsional vibration of a back-to-back gearbox system has been simulated in the time domain, using time domain receptance theory. Receptance analysis in the time domain is an extension of the frequency domain method and allows the benefits of a systems approach for modelling complicated systems. Meshing spur gears represent a complicated dynamic system. The excitation from the variation in gear mesh stiffness has been considered in the present model. A gear mesh kinematic simulation was developed to simulate the contact pattern and mesh stiffness for a spur gear pair with a contact ratio of less than 2.0. The time domain receptance model was verified using a simulated white noise input to generate frequency response functions up to 1600 Hz. The simulated torsional natural frequencies were compared with the experimentally measured results in Part 1 [1]. After the adjustment of model parameters, the first eight torsional natural frequencies were accurately matched by the predictions of the time domain model. The simulated frequency response functions of the time domain model accurately matched the frequency response functions from the frequency domain receptance model presented in Part 1 [1].
Valve-train dynamics: A simplified tribo-elasto-multi-body analysis
Authors: Kushwaha M , Rahnejat H , Jin Z M
Published: October 2002

This paper presents a model of a cycloidal cam-flat follower pair. The model incorporates the inertial elements, the assembly constraint functions and the sources of compliance in the valve train. The sources of compliance include the valve spring characteristics, including the spring surge effect under dynamic conditions, as well as the contact compliance between the cam and the flat follower. The contact domain is treated as a counterformal concentrated lubricated region subjected to an elasto-hydrodynamic regime of lubrication (EHL). The prevailing contact geometry is one of finite line contact.

The paper presents the results of simultaneous solution of the Lagrangian dynamics for the non-linear constrained system, together with an approximate quasi-static elastohydrodynamic solution of the lubricated contact conjunction at each time step by an extrapolated oil-film thickness formula for combined entraining and squeeze film action. The effect of spring surge on the contact separation and residual vibrations of the system are investigated, as well as the lubricant pressure distribution and film thickness, including during start-up and acceleration.
Vibration analysis of a test rig for a radial compressor
Authors: Lee S U , Robb D , Besant C
Published: October 2002

A radial compressor has been designed at Imperial College for cooling a high-speed generator (HSG) coupled directly to a small gas turbine engine to produce 100kW electric power. The compressor has a significant influence on the overall dynamics of the generator. Therefore, it is designed to be lightweight for rotor-dynamic reasons together with reasonable aerodynamic efficiency. An experimental rig for the compressor performance testing was also designed. In order to operate this rig safely, it is very important to be able to predict and analyse its dynamic behaviour. For this purpose, a systematic procedure was used to develop a finite element (FE) model to predict natural frequencies under operating conditions. In the procedure, the relationship between FE analyses, modal analyses and results of a running test are established. Vibration analyses of the compressor rig using the proposed procedure are carried out. Finally, the results of computations and experiments for the rig are presented and compared.
Kinematics of transmissions consisting of an outboard ball joint and an inboard generalized tripod joint
Authors: K'nevez J-Y , Mariot J-P , Moreau L , Diaby M'P
Published: October 2002

This paper presents the kinematics of transmissions consisting of an outboard ball joint close to the wheel and a tripod joint close to the gearbox. Emphasis is placed on the intrinsic properties of the tripod joint owing to the orthogonality between the tripod legs and the intermediate shaft. In particular, it is shown that the roller-tripod centre distances are available analytically with a mere dependence on the intermediate shaft rotation angle and the joint angle. For the whole transmission, the kinematics reduces to two non-linear equations with the upper two angles as unknowns. Following numerical simulations, an approximate solution is proposed for evaluating the departure from constant velocity behaviour. A generalized joint derived by bending the tripod legs and the tulip ramps is introduced, and the influence of these geometrical modifications on the roller-to-tripod centre distances is shown. Optimization techniques based on evolutionary algorithms have been introduced for minimizing the generation of vibrations caused by roller-to-tripod movements. In many of the examples shown, geometric approaches have been used both for illustration and calculation.
Dynamic response of adhesively bonded single-lap joints with a void subjected to harmonic peeling loads
Authors: Vaziri A , Hamidzadeh H R , Nayeb-Hashemi H
Published: October 2002

The only viable method to join some components is by using adhesives. These components are often subjected to dynamic loading, which may cause initiation and propagation of failure in the joint. In order to ensure the reliability of these structures, their dynamic response and its variation with the presence of defects in the bonded area must be understood.

The dynamic response of a single-lap joint subjected to an out-of-plane harmonic force is evaluated. The bonded joint is modelled as a Euler-Bernoulli beam joined with an adhesive and constrained at one end and subjected to a harmonic force at the free end. The results show that the system response is not sensitive to a range of adhesive loss factor of 0-1. Furthermore, the system response is little affected by the presence of void in the bond area. The system response seems to be more sensitive to the void location than to its size. Peel and shear stresses in the bond area are obtained and found to be confined to the edge of the overlap. For the adhesive and adherent properties and geometries investigated the maximum peel and shear stresses in the bond area are little affected by the presence of a central void, covering up to 60 per cent of the overlap length for all applied loading frequencies. However, when the frequency of the applied load is close to the natural frequencies of the structure, a void may increase or decrease both the maximum peel and shear stresses.
Design optimization of the linkage dimension for a hybrid-type parallel kinematic machine tool
Authors: Chang T-H , Chen S-L , Kang C-A , Inasaki I
Published: October 2002

The parallel kinematic machine tool has many advantages including excellent loading capacity, high structural stiffness and small accumulated error of linkage. It has become one of the most important research fields for machine tools. In the present research, a principle for the optimization of the dimensional design parameters of a parallel kinematic machine tool is proposed. A five-degree-of-freedom (5DOF) parallel kinematic machine tool with a TRR-XY hybrid mechanism is chosen for investigating the design procedures and the optimization results. The inverse kinematics of the hybrid mechanism is first investigated. Then, the inverse solution is used to analyse and create the workspaces of the machine tool. The design parameters of the mechanical components are further optimized for constructing the maximum workspace.
Actuator driving force analysis and modelling of TRR-XY PKM
Authors: Chang T-H , Chen S-L , Chang Y-C , Inasaki I
Published: October 2002

The main aim of this work is to investigate the actuator driving force variations of a parallel kinematic machine (PKM) for different cutting paths. To meet this aim, a TRR-XY five-degrees-of-freedom (5DOF) PKM was selected and built for this research, and a dynamic analysis model of the PKM was developed. Here, ‘T’ stands for translational DOF and ‘R’ stands for rotational DOF of the platform. In this research, the dynamic analysis and modelling for the TRR-XY PKM are derived on the basis of the Denavit-Hartenberg (D-H) notation method. The parametric tool concept and Lagrange equation theory are also included in the derivation. The actuator driving force variations for different cutting paths are obtained using the developed dynamic modelling. Five cutting paths are selected to represent the possible cutting paths inside the workspace. The obtained actuator driving force variations on A, B, C chains are useful for obtaining a good dynamic performance PKM machining application. The main results show that the required actuator driving forces are mainly affected by the inclination angle, ϕ of the tool platform. The angular acceleration of the tool platform has only very little effect. For obtaining a better PKM machining application, a working space with smaller ϕ is recommended.
Practical considerations for the static balancing of mechanisms of parallel architecture
Authors: Ebert-Uphoff I , Johnson K
Published: October 2002

This paper discusses the development of statically balanced spatial parallel platform mechanisms. A mechanism is statically balanced if its potential energy is constant for all possible configurations. This property is very convenient for robotic manipulators with large constant payloads, since it means that the mechanism is statically stable for any configuration, i.e., zero actuator torques are required whenever the manipulator is at rest. Furthermore, only inertial forces and moments have to be sustained while the manipulator is moving. This makes it possible to create passive devices that can assist humans to manipulate a heavy load, and to create robotic manipulators that require smaller actuators and/or consume less energy. Furthermore, by retrofitting existing machine tools, static deflection problems due to gravitational loads may be reduced.

This paper (1) summarizes how static balancing can be implemented in a parallel manipulator with six degrees of freedom, (2) presents the design of a small-scale prototype, and (3) discusses general implementation issues.
The incorporation of damping in lumped-parameter modelling techniques
Authors: Mostofi A
Published: October 2002

In structural dynamics modelling by means of multidegrees-of-freedom systems within the scope of lumped-parameter techniques, masses and stiffnesses are easily quantifiable, while methods of incorporating damping have traditionally been based on tentative approaches. Here a rigorous technique is proposed where the energy loss per cycle is simulated by a convenient mathematical scheme of representing the viscous dampers as proportional to mass and stiffness values. The level of damping at any one or two selected frequencies can then be controlled. Although the concept is not original, the novelty here is due to its proposed applicability to the lumped-parameter idealizations such as finite elements or mechanical simulation packages.
Visioplastic analysis of experimental rolling of steel
Authors: Rodríguez-Rodríguez M G , Valdés-Covarrubias E , Zambrano P C , Guerrero-Mata M P , Colás R
Published: October 2002

A visioplastic analysis was carried out in hot rolled samples of different types of steel to study the way strain distributed during deformation. The studies were conducted on wedge-shaped specimens that were cut along their mid-plane, inscribed with a grid, spot welded at both ends and hot rolled in a two-high experimental mill. The coordinates of the nodal points in the grid were measured prior to rolling and after the samples cooled down to room temperature after deforming. This was done by photographing and digitizing the specimens, the spread that resulted from rolling was measured and used to correct the equivalent values of strain. The local components of strain were evaluated from both sets of coordinates. It was found that the distribution of strain followed different patterns, the shear and equivalent components were higher towards the surface, whereas the normal components show a distribution related to the reduction imparted.
Optimum design of laminated composites subjected to hygrothermal residual stresses
Authors: Khalil M , Bakhiet E , El-Zoghby A
Published: October 2002

Residual stresses in composite laminates depend on the thermoelastic properties of the material and processing temperatures. The distribution of these stresses in the various laminates is a function of the stacking sequence and ply orientation. This paper presents a theoretical investigation of the effects of hygrothermal residual stresses on the optimum design of laminated composites. Angle-ply laminates, cross-ply laminates and quasi-isotropic laminates have been considered and these laminates are subjected to different mechanical, thermal and hygroscopic loading conditions. Optimum laminate configurations have been determined by using non-linear optimization algorithms offered by the program OPTICOM. Residual stresses and strains in different layers of laminates are calculated using classical laminate theory and laminate strength ratios are determined by using the Tsai-Wu failure criterion. Hygrothermal effects on minimum thickness and in-plane strength of the laminates are then demonstrated. Analysis of the results indicates that the prediction and measurement of residual stresses are important in relation to production, design and performance of composite structures.
Effects of exhaust gas recirculation in homogeneous charge compression ignition engines
Authors: Nakano M , Mandokoro Y , Kubo S , Yamazaki S
Published: October 2002

Ignition control is an important issue in homogeneous charge compression ignition (HCCI) engines, which have the advantages of low NOx emission and high thermal efficiency. In this study, the effect of the exhaust gas recirculation (EGR) on the ignition control of HCCI engines is discussed using an engine cycle simulation in which a homogeneous mixture is assumed. Auto-ignition of 65 per cent iso-octane + 25 per cent toluene + 10 per cent n-heptane, which is used as a fuel to evaluate the characteristics of a gasoline-like fuel, is represented by a detailed reaction model.

The dilution by EGR delays the ignition timing when the charged gas temperature is not changed by EGR. The temperature rise of the charged gas promotes auto-ignition. Based on these characteristics, it was suggested that the ignition timing could be controlled by EGR with temperature control, when the amount of fuel supply is constant.

This control method can also be applied to control of the air-fuel ratio (A/F) in the cylinder while maintaining the optimum ignition timing. In spite of the difference in the A/F and the EGR ratios, no significant difference was found in the pressure rise rate at combustion and the NOx emission when the ignition timing was the same.
Characterization of lean combustion instability in premixed charge spark ignition engines
Authors: Wagner R M , Drallmeier J A , Daw C S
Published: October 2002

The focus of this study was to identify and characterize the development of lean combustion instability in spark ignition engines. Statistical techniques from non-linear dynamics were used to process experimental combustion observations to reveal previously unrecognized patterns in cycle-to-cycle combustion variations. The presence of non-linear deterministic structure was confirmed in lean combustion variations from a single cylinder research engine and a four-cylinder production engine. The transition to non-linear deterministic behaviour appeared to occur via a period-doubling bifurcation sequence. Over the bifurcation region, engine dynamics appeared to pass through distinct dynamic stages including stochastic, periodic and possibly chaotic behaviour. The level of dynamic complexity and corresponding cycle-to-cycle communication were found to be a strong function of the residual gas fraction. Experimental observations were also compared with patterns predicted by a recently proposed low-order engine model. Further analysis of the time-series results indicated that the engine frequently exhibited complicated repeating combustion patterns 15 to 20 cycles in length under certain lean operating conditions. Similar dynamics were seen for the two very different engine designs. The work suggests that the underlying cyclic dynamics may not be dependent upon the details of such processes as mixing and combustion but are characteristic of all lean premixed spark ignition engines.
A study of ignition delay of diesel fuel sprays
Authors: Kobori S , Kamimoto T , Aradi A. A.
Published: October 2002

Diesel fuel ignition delay times were characterized in a rapid compression machine (RCM) using cylinder ambient gas temperature and pressure measurements as diagnostics. The objective of the study was to investigate the dependency of ignition delay time on: (a) cylinder ambient gas temperature, (b) cylinder ambient gas pressure, (c) injection pressure, (d) injector nozzle orifice diameter, (e) base fuel cetane number and (f) 2-ethylhexyl nitrate (2-EHN) cetane improver additive. The results presented here show that diesel ignition delay times can be shortened by increasing cylinder gas ambient temperatures and pressures, injection pressures and base fuel cetane number, either through blend components or by addition of cetane improver. Decreasing the injector nozzle orifice diameter also decreases the ignition delay time. It was also found that ignition chemistry is rate controlled by the molar concentration of the cylinder gas oxygen.
Spray/wall interaction models for multidimensional engine simulation
Authors: Han Z , Xu Z , Trigui N
Published: October 2002

Models were developed to describe the spray wall impingement processes that take place in internal combustion engines. In this report focus is placed on the model formulation and experiment assessment of the spray/wall interaction submodels. It is identified that the Leidenfrost phenomenon is very unlikely to occur in a spark ignition (SI) engine including stratified-charge operation in a direct injection spark ignition (DISI) engine. A more comprehensive splashing/deposition threshold function is proposed to include the effects of surface roughness and pre-existing liquid film. Based on the wave phenomena observed on the surface of the liquid crown formed during drop impingement, a new splash breakup model is developed using linear instability analysis. The predicted drop size agrees well with available single-drop impingement experimental data. A new formulation for the post-impingement droplet velocity is also given which uses statistical sampling and jet impingement theory. The proposed models were assessed by comparing computations with two sets of experimental sprays impinging on a flat plate with the use of a pintle nozzle injector for port fuel injection (PFI) engines. The computed spray shape, normal and tangential penetration and droplet size show good agreement with experimental data.
Large eddy simulations of in-cylinder turbulence for internal combustion engines: A review
Authors: Celik I , Yavuz I , Smirnov A
Published: October 2002

While engineering applications of the large eddy simulation (LES) technique are becoming a common reality in many branches of engineering and science, its application to engine flows has lagged behind due to the relatively more complex nature of both the flow and the geometry relevant to in-cylinder flows. In this paper a review of the limited number of LES applications to engine flows is given, and most significant results from these studies are presented. Also, the LES formulation appropriate for engine applications is briefly described, along with the main characteristics of in-cylinder flows. As expected, engine applications of LES are not of the so-called ‘high-fidelity’ type, but rather they employ formally second-order accurate numerical schemes in conjunction with finite volume formulation. The subgrid scale (SGS) models used are also kept as simple as possible, mostly using a variant of the Smagorinsky model. Nevertheless, this review reveals that even with relatively coarse grids, LES captures much more interesting features of in-cylinder flows, such as the large coherent vortical flow structures developed during the intake stroke. In the opinion of the present authors, a low-resolution LES provides a better solution than RANS (Reynolds averaged Navier-Stokes) with moderate grid resolution because the important features of flow dynamics cannot be reproduced in RANS due to the high level of non-physical diffusion. Of course, some overheads in computational costs must be paid for this benefit obtained from LES.
Investigation on exhaust emissions of a common rail high-speed direct injection diesel engine running with dimethyl ether
Authors: Maroteaux F , Descombes G , Sauton F , Jullien J
Published: October 2002

This research investigates engine performance and the potential to reduce exhaust emissions by using dimethyl ether (DME) as an alternative fuel to diesel for compression ignition engines. The main objective of this study it to evaluate on a test-bed the performance and emissions reduction potential of a four-cylinder passenger car HSDI common rail turbocharged diesel engine running with DME in the absence of specific modifications to the engine itself but some modifications to the fuel injection system.

The results obtained from this engine running with DME using diesel fuel as reference are encouraging. In the next phase of this study the injection rate will be adapted to DME operation and to the geometric and thermodynamic conditions of the combustion process. A study of combustion reaction is also necessary in order to optimize the turbocharging system for exclusive DME operation.
Modelling characteristics of gasoline wall films in the intake port of port fuel injection engines
Authors: Zhu G-S , Reitz R D , Xin J , Takabayashi T
Published: October 2002

Models were developed to describe the vaporization of well-mixed wall films of multi-component engine fuels based on continuous thermodynamics and applied to describing multi-component fuel spray-wall interactions. All the models were implemented into the KIVA3V Release 2.0 code. Validation calculations were conducted for pulsed injection cases and compared with experimental wall film thickness data under different air-fuel ratios and inflow conditions in an inclined pipe, which simulates an intake port of port fuel injection engines. Calculations with single-component iso-octane fuel were also conducted for comparison. The influence of wall temperature, inflow-air velocity and injection angle on the gasoline wall film characteristics was studied. The results indicate that the multi-component fuel film is composed of increasingly heavy species as the vaporization proceeds. The fuel-film structure which results from spray-pipe-wall interaction is greatly different from that resulting from spray-plane-wall interaction. An increase in the wall temperature significantly decreases both the film thickness and the film area. The injection angle significantly changes the wall film structure. Although the inflow velocity enhances the fuel vaporization rate, it has a relatively small effect on the fuel film movement along the pipe wall.
Measurement of particulate matter from diesel engine exhaust using a tapered element oscillating microbalance
Authors: Gilbert M S , Clark N N
Published: October 2002

Acquisition of real-time particulate matter (PM) data is proposed by the use of a Rupprecht and Patashnick Company, Inc. Series 110 diesel particulate monitor tapered element oscillating microbalance (TEOM) mass measuring device. The objectives of using a TEOM diesel particulate analyser were to validate its collection capability and evaluate its real-time transient characteristics. Conventional PM measured using dilute diesel exhaust filtration was used as the base line for evaluating the TEOM collection capability. Real-time mass rate data were separated into positive and negative values, then integrated over the duration of the test. The integrated positive mass was divided by the integrated negative mass to create a ratio that is indicative of real PM collected versus moisture released from the filter. Tests were performed on heavy-duty diesel engines on a stationary dynamometer using the US Heavy Duty Federal Test Procedure speed and load cycle. TEOM sample tube temperatures at 35°C yielded the best TEOM-conventional PM filtration mass ratio. However, as sample path temperatures decreased, a decrease in the positive-negative mass ratio occurred. A compromise between conventional filter agreement and real-time data was made in selecting the temperature set point of 40°C as the most desirable sampling temperature. The sample flowrate was varied from one to four litres per minute. A comparison of the TEOM with a conventional filter decreased as the TEOM flow increased. The 1 l/min set point provided the best TEOM-conventional filtration ratio. The positive-negative mass ratio increased as flow decreased. The flow-rate of 3 l/min was chosen to be a compromise between the TEOM-conventional filtration mass ratio and real-time results. The best TEOM-conventional filtration ratio measured was 0.97. The best set of test results was a three-test averaged TEOM-conventional filtration ratio of 0.92 with a coefficient of variance of 0.15 per cent.
Development of a liquid natural gas pump and its application to direct injection liquid natural gas engines
Authors: Goto Y
Published: October 2002

Direct injection gas engines operated with liquid natural gas (LNG) look promising because the energy density-volume ratio of LNG is three times higher than that of compressed natural gas (CNG) and pressurization of LNG to injection pressures is much easier and expends less energy. Based on these considerations, a prototype of an LNG high-pressure pump, which can achieve a pressure as high as 20 MPa, was developed and tested using nitrogen instead of LNG. It was confirmed that the energy consumption of the LNG pump to pressurize an amount of natural gas is one-eighth the energy consumption of the corresponding CNG pump.

A direct injection natural gas engine having a 108 mm bore and a compression ratio of 12 was developed for the evaluation of its performance and emissions. The result of the engine experiment made it clear that the indicated thermal efficiency of the gas engine is approximately 44 per cent over a medium and high load range, which is equivalent to that of the corresponding diesel engine. Since the energy required for pressurizing LNG to 15 MPa is 2–3 per cent of the indicated power of the engine, the LNG engine proposed is considered to have the same level of brake thermal efficiency as the corresponding diesel engine. If a truck vehicle is powered by the direct injection LNG engine and carries an LNG tank with a capacity 1.5 times larger than that of gas oil, the cruising distance of the vehicle could be the same as that of a diesel truck.
Study of nozzle characteristics on the performance of a small-bore high-speed direct injection diesel engine
Authors: Lyu M-S , Shin B-S
Published: October 2002

As Co2 emissions from vehicles are gaining global attention, the low fuel consuming powertrain is in much greater demand than before. Some alternatives are suggested but the high-speed direct injection (HSDI) diesel engine would be the most realistic solution. Vehicle simulation shows that a car with low fuel consumption can be realized by applying a 1–1.2 L high-speed direct injection diesel engine in vehicles weighing about 750 kg. Although the direct injection diesel engine has been researched for a long time, enhancement of mixing between air and fuel in a limited space makes it a challenging area to develop a small swept volume HSDI diesel engine. The authors are investigating small HSDI diesel engine combustion technologies in an effort to realize a low fuel consumption vehicle. The main objective in this study is to obtain a better understanding of the combustion-related parameters from such a small size HSDI diesel engine in order to improve engine performance.
Engine thermomanagement with electrical components for fuel consumption reduction
Authors: Cortona E , Onder C. H. , Guzzella L
Published: October 2002

This paper proposes a solution for advanced temperature control of the relevant temperature of a combustion engine. It analyses the possibility of reducing vehicle fuel consumption by improving engine thermomanagement.

In conventional applications, combustion engine cooling systems are designed to guarantee sufficient heat removal at full load. The cooling pump is belt-driven by the combustion engine crankshaft, resulting in a direct coupling of engine and cooling pump speeds. It is dimensioned such that it can guarantee adequate performance over the full engine speed range. This causes an excessive flow of cooling fluid at part-load conditions and at engine cold-start. This negatively affects the engine efficiency and, as a consequence, the overall fuel consumption. Moreover, state-of-the-art cooling systems allow the control of the coolant temperature only by expansion thermostats (solid-to-liquid phase wax actuators). The resulting coolant temperature does not permit engine efficiency to be optimized.

In this paper, active control of the coolant flow as well as of the coolant temperature has been realized using an electrical cooling pump and an electrically driven valve which controls the flow distribution between the radiator and its bypass. For this purpose, a control-oriented model of the whole cooling system has been derived. Model-based feedforward and feedback controls of coolant temperature and flow have been designed and tested. With the additional actuators and the model-based control scheme, a good performance in terms of fast heat-up and small temperature overshoot has been achieved.

The improvements in fuel consumption obtained with the proposed configuration have been verified on a dynamic testbench. Both engine cold-start under stationary engine operation and the European driving cycle MVEG-A with engine cold-start were tested. The fuel consumption reductions achieved during these tests vary between 2.8 and 4.5 per cent, depending on the engine operating conditions. Compared to vehicle mass reduction or internal engine improvements, engine thermomanagement is a simple, flexible and cost efficient solution for improving system performance, i.e. fuel consumption.