bluuebunny/crossref_metadata_2025_split huggingface dataset:
A new isothermal theory for Stirling machine analysis and a volume optimization using the concept of ‘ancillary’ and ‘tidal’ domains
Authors: Finkelstein T 
Published: October 2002

Theoretical studies of Stirling cycle machines have always utilized a topological system view that goes back to Schmidt's isothermal analysis, where the process is analysed by reference to the expansion space volume variations. Due to this idiosyncrasy in the formulation, it has been difficult to deduce meaningful design criteria from the results. In this paper an alternative visualization is presented, using the newly introduced concepts of a ‘tidal phase angle’ and overlapping ‘tidal’ and ‘ancillary’ domains. With vectorial parameters and a centralized reference basis, a non-dimensional parameter Rcaronfr;tcr, the ‘tidal compression ratio’, equal to the ratio of the average masses in the tidal and ancillary domains, is derived. This number uniquely characterizes the operation of equivalent machines and is therefore akin to the compression ratio in internal combustion engines. On the basis of this, a second new parametric grouping emerged to enhance the usefulness of the resultant integrated equations for use with dimensional analysis. It was defined as the ‘specific performance’ Rcaronfr;sp and is proportional to the output per unit mass, the gas constant and the operating temperature range. It is applicable to engines, heat pumps and refrigerators. Prior attempts at optimizing the proportions of a Stirling engine have not yielded usable results and consequently nearly all Stirling cycle machines built up to the present time have expansion and compression spaces of equal size. The new analysis shows that this is not the most appropriate configuration and it readily yields an optimization of the component volumes. One single analytical conditional equation for the optimum relative sizes of the constituent spaces was obtained from the new formulation for performance that quantifies the condition for an optimized proportioning of any Stirling cycle machine. It has three distinct usable solutions, one of which is an analytical confirmation of a postulate that has previously been published by the author without proof, equating VE/ VC and also Vh/ Vk to the temperature ratio TE/ TC. A numerical verification of this rule based on the proportions of the United Stirling V-160 engine compares it with 12 equivalent re-proportioned derivative engines, all with equal charge masses and operating at precisely the same conditions. This shows a substantial increase in the ideal performance through the use of the derived criteria. The main conclusion is that this theory may lead to a re-examination of the overall layout of Stirling cycle machines and the emergence of a new class of machines with superior performance.
Temperature stresses in thick circular cylindrical shells used in nuclear reactors with exponential heat generation within the shell wall thickness
Authors: Guerreri G , Cossa L M 
Published: October 2002

In the preceding paper, formulae and graphs were given which enabled estimates to be made of heat flow, temperature and stresses through the thickness of the circular cylindrical shell, when heat was not generated inside the thickness and when it was generated according to a uniform path. Situations of heat generation in shell thickness are commonly encountered in the shields of nuclear reactors. All the expressions given for stress in the preceding paper may be reduced to the following form: σ{ Eα qa2/[(1 - ν) k]}η, where η is a factor associated with the stress which depends upon heat generation profiles, internal and external temperatures T a and T b of the shell and its thermal conductivity k, for each radius r. Another common heat generation which occurs in these shells has an exponential path. For these cases, the circumferential thermal stress σϑ may be given in the following form: σϑ = { Eα q(β−1)2/[(1 - ν) k]}ηϑ, where β is the exponential absorption factor which is related to the quantitative measure of the generated heat and ηϑ is the non-dimensional circumferential stress. In the present paper graphs are furnished to estimate the parameter ηϑ in order to foresee the values of stresses in the circumferential directions at the internal and external radii of the shell for the case of exponential heat generation through the wall thickness. They apply only when: (a) all generated heat flows inside the vessel or (b) all heat flows outside the vessel or ( c) T a = T b. Application of the principle of superposition shows how to evaluate the stresses where the generated heat paths are not uniform, triangular or exponential.
Design of low-reaction steam turbine blades
Authors: Walker P. J. , Hesketh J. A. 
Published: October 2002

Optimizing the aerodynamic design of turbine blades is a compromise between a large number of issues. These can be grouped into three areas: (a) aerodynamic compromises; e.g. increasing the pitch—chord ratio improves profile loss but worsens secondary loss, (b) mechanical constraints; e.g. the pitch-chord ratio affects the strength of a profile, which for a given unsteady stress level determines the width and hence strongly influences the secondary loss, (c) costs; e.g. increasing the number of stages improves performance but also increases the cost of the turbine. It can also affect rotor stability and even the size of the turbine hall. Some of the issues are difficult to quantify and may vary from day to day. For example, the marginal manufacturing cost of a given design will depend on the load on particular machine tools. Therefore the approach of a manufacturer evolves from experience. However, many other issues can be addressed systematically to achieve near optimum designs. This paper explores the aerodynamic design of low-reaction steam turbine blades and describes the technical arguments that lead to design decisions. Where the decision depends on cost and mechanical constraints these are also explored. A typical low-reaction stage is shown schematically in Fig. 1. The paper will concentrate on the design of short and intermediate height blades typically used in HP and IP cylinders and in the early stages of LP cylinders. In practice, long blades typically used in the later stages of LP cylinders are fairly similar for both ‘reaction’ and ‘impulse’ design manufacturers.
Gear transmission error outside the normal path of contact due to corner and top contact
Authors: Munro R. G. , Morrish L , Palmer D 
Published: October 2002

This paper is devoted to a phenomenon known as corner contact, or contact outside the normal path of contact, which can occur in spur and helical gear transmission systems under certain conditions. In this case, a change in position of the driven gear with respect to its theoretical position takes place, thus inducing a transmission error referred to here as the transmission error outside the normal path of contact (TEo.p.c). The paper deals with spur gears only, but the results are directly applicable to helical gears. It systematizes previous knowledge on this subject, suggests some further developments of the theory and introduces the novel phenomenon of top contact. The theoretical results are compared with experimental measurements using a single flank tester and a back-to-back dynamic test rig for spur and helical gears, and they are in good agreement. Convenient approximate equations for calculation of TEo.p.c suggested here are important for analysis of experimental data collected in the form of Harris maps. This will make possible the calculation of tooth stiffness values needed for use in theoretical models for spur and helical gear transmission systems.
The automotive connector: The influence of powering and lubricating a fretting contact interface
Authors: Swingler J 
Published: October 2002

The increasing amount of telematic and other electronic systems in the modern motor vehicle demands higher performance and reliability in ever decreasing space. Over many years, connector technology has advanced but is still regarded as the weak link in the reliability chain. Fretting corrosion is thought to be the main failure mechanism causing intermittent high contact resistance. A low-frequency fretting apparatus is used in this study to induce fretting corrosion on contact samples. Low frequency is used to simulate the effect caused by different thermal expansion of connector components. Powering the contact interface under these fretting conditions delays the onset of high contact resistance. Joule heating is expected to accelerate surface oxidation, but electrical breakdown of films dominated at the levels studied (2 A, 12 V open circuit). Lubricating the interface also improves performance which is shown to be due to at least three contact enhancement mechanisms: wear reduction, oxidation retardation and improved debris dispersal.
The UK road user charging technology trials: A review
Authors: Stoneman B 
Published: October 2002

The department of the Environment, Transport and the Regions (DETR) has embarked on a programme of research into road user charging. The first phase of the programme took place at the research track facility of the Transport Research Laboratory (TRL) between November 1996 and June 1997. Technology trials were undertaken with two electronic fee collection (EFC) systems supplied by Bosch Telecom Gmbh and GEC-Marconi Communications. The trials investigated the ‘front end’ of tolling systems, namely the tolling transaction, violator detection and vehicle classification components. This paper describes the trials design and the preparation of an infrastructure at the test track suitable for trials of both motorway and urban road charging systems. A dedicated trials support system was configured and comprised a trials computer system a video monitoring system, a vehicle location system and an environmental monitoring station. Trials scripts were developed for a range of trials scenarios and used as the basis for testing the EFC systems with a range of vehicle manoeuvres, including manoeuvres not possible on a live motorway. The trial programme provided the opportunity to investigate the technologies and the potential of EFC systems for application on the UK motorway network. In parallel with the test track trials programme, a separate and wide-ranging programme researched specific tolling-related issues which were reported to the DETR to provide additional information on the tolling technologies and to support policy development. The next phase of the UK charging programme is also discussed following the Government's White Paper on the future of transport.
In-cylinder studies of the effects of CO2 in exhaust gas recirculation on diesel combustion and emissions
Authors: Zhao H , Hu J , Ladommatos N 
Published: October 2002

This paper reports the results of the effects of CO2 in exhaust gas recirculation (EGR) on diesel combustion and emissions. The experiments were carried out on a specially designed single-cylinder diesel engine. In-cylinder measurements were obtained from the optically accessible swirl chamber using high-speed shadowgraphy, the two-colour method and laser extinction. Furthermore, in-cylinder pressure measurements from the combustion chambers were used to derive the heat release rates during combustion. Two experiments were carried out on the effects of CO2 on diesel combustion and pollutant formation. In the first series of experiments, CO2 was used to replace some of the oxygen in the intake mixture, which simulated the dilution effect of conventional EGR. This so-called replacement EGR method was characterized by the typical NOx and smoke trade-off, where NOx reduction was accomplished at the expense of exhaust smoke. In the second series of tests, CO2 was added to the intake charge so that the oxygen concentration in the combustion chamber was not affected. In this additional EGR method, CO2 was found to suppress both NOx and smoke emissions. The mechanisms of these two different EGR modes on diesel combustion and emissions were examined using the above in-cylinder measurement techniques and exhaust emission analysis.
Effect of synchronized secondary air injection on exhaust hydrocarbon emission in a spark ignition engine
Authors: Sim H. S. , Min K. , Chung S. H. 
Published: October 2002

A synchronized secondary air injection (SAI) method has been proposed to reduce hydro- carbon (HC) emission by injecting secondary air intermittently into the exhaust port. The method has been tested in a single-cylinder spark ignition engine operating at cold-steady/cold-start conditions. HC concentration and exhaust gas temperature were monitored with a fast-response flame ionization detector and with thermocouples respectively. Effects of exhaust air-fuel ratio (A/F), engine A/F, spark timing and air injection timing have been investigated and the results are compared with a continuous SAI method and the baseline condition. Results show that HC reduction rate and exhaust gas temperature are sensitive to the timing of synchronized SAI. Two optimum SAI timings are observed which are at 100° crank angle (CA) after top dead centre (ATDC) and 230° CA ATDC depending on spark timing. At the cold-steady condition, the synchronized SAI is found to be more effective in HC reduction and also has much higher exhaust gas temperature than either the continuous SAI or the baseline condition. At the cold-start condition when a catalyst is not used, the accumulated HC emission during the first 120 s decreases by about 55 per cent with the synchronized SAI compared with that of the baseline condition, while the result with the continuous SAI is comparable with the baseline condition.
Analysis of flame kernel development with Schlieren and laser deflection in a constant volume combustion chamber
Authors: Song J , Sunwoo M 
Published: October 2002

The purpose of this study is to investigate the relation between ignition systems (or energy) and flame kernel development. In this research, three different kinds of ignition systems and several different kinds of spark plug electrodes are designed and manufactured. The flame propagation velocity in a constant volume combustion chamber is measured by both a laser deflection method using an He-Ne laser and a Schlieren method using a high speed digital camera. In order to control the ignition energy, the dwell time is varied by a spark time controller. The results indicate that, when the ignition energy is increased by extending the dwell time, flame kernel growth accelerates. As the electrode gap width is increased, the breakdown energy is also increased, which stimulates the initial kernel development. The materials, diameter and shape of the electrode affect the discharged energy, the energy transfer efficiency and heat losses and, thus, these also affect the flame kernel development. The average difference in measurement of the flame velocity by the laser deflection method and Schlieren method is only 1.73 per cent. The laser deflection method is found to be preferable because it is more effective and employs simpler means for the analysis of flame kernel development.
Differential stress modelling of turbulent flows in model reciprocating engines
Authors: Lea C. J. , Watkins A. P. 
Published: October 2002

A study is made here of the application of a differential stress model (DSM) of turbulence to flows in two model reciprocating engines. For the first time this study includes compressive effects. An assessment between DSM and k-ɛ results is made comparing with laser Doppler anemometry experimental data of the mean flow and turbulence intensity levels during intake and compression strokes. A well-established two-dimensional finite-volume computer code is employed. Two discretization schemes are used, namely the HYBRID scheme and the QUICK scheme. The latter is found to be essential if differentiation is to be made between the turbulence models. During the intake stroke the DSM results are, in general, similar to the k-ɛ results in comparison to the experimental data, except for the turbulence levels, which the DSM seriously underpredicts. This is in contrast to a parallel set of calculations of steady in-flow, which showed significant gains from using the DSM, particularly at the turbulence field level. The increased number of grid lines employed in those calculations contribute to this apparent difference between steady and unsteady flows, but cycle- to-cycle variations are more likely to be the primary cause, resulting in too high levels of turbulence intensity being measured. However, during the compression stroke the DSM returns vastly superior results to the k-ɛ model at both the mean flow and turbulence intensity levels. This is because the DSM generates an anisotropic shear stress field during the early stages of compression that suppresses the main vortical structure, in line with the experimental data.
Automotive active suspensions Part 1: Basic principles
Authors: Williams R A 
Published: October 2002

Automotive suspension design is a compromise brought about by the conflicting demands of ride and handling. The past few years have seen the introduction of increasingly sophisticated, electronically controlled, components into automotive suspensions which redefine the boundaries of the compromise. The paper has been written in two parts. This first part reviews the compromises which are required in the design of a conventional passive suspension. It then goes on to show how those compromises can be changed by the inclusion of active components. The second part discusses the hardware employed which ranges from simple switched dampers, through semi-active dampers, and low bandwidth/soft active suspensions, to high bandwidth/stiff active suspensions. The benefits to be derived from each of the technologies will be assessed, together with their strengths and weaknesses.
Measurements of in-cylinder mixture strength and fuel accumulation in the inlet port of a gasoline - injected engine during very rapid throttle openings
Authors: Ladommatos N , Rose D 
Published: October 2002

The mixture strength in a cylinder of a port-injected gasoline engine was monitored continuously during very rapid throttle openings. The data on mixture strength were combined with other engine data collected in order to obtain for each successive engine cycle: the air—fuel ratio within the cylinder and the change in the fuel mass accumulating on the inlet port of the cylinder being monitored. The four-cylinder spark-ignition engine used had a displacement of 1.6 litre, four valves per cylinder and multipoint sequential fuel injection controlled by an electronic management system programmed for three - way catalyst operation. All tests were conducted with the engine coolant at the temperature of 90°C and at a constant engine speed of 2000 r/min. The engine transient involved very rapid throttle openings which were completed within about 15 ms. Small and large throttle openings were investigated along with the effect of altering the type and condition of the fuel injectors. The engine response to the fast throttle opening comprised a sharp rise in the air—fuel ratio (maximum gravimetric air—fuel ratio of around 25:1) which lasted for only a single cycle, followed by a drop in the air-fuel ratio (minimum air—fuel ratio of about 10:1) and, subsequently, a gradual rise towards a stoichiometric air—fuel ratio within about 10 engine cycles.
Optimization of the tractive performance of four-wheel-drive tractors: Theoretical analysis and experimental substantiation
Authors: Wong J. Y. , McLaughlin N. B. , Knezevic Z , Burtt S 
Published: October 2002

The results of a theoretical analysis reveal that, for a four-wheel-drive tractor to achieve the optimum tractive performance under a given operating condition, the thrust (or driving torque) distribution between the front and rear axles should be such that the slips of the front and rear tyres are equal. For four-wheel-drive tractors with rigidly coupled front and rear drive axles, this can be achieved if the theoretical speed (the product of the angular speed and the free-rolling radius of the tyre) of the front and that of the rear wheels are equal or the theoretical speed ratio is equal to 1. Field test data confirm the theoretical findings that, when the theoretical speed ratio is equal to 1, the efficiency of slip and tractive efficiency reach their respective peaks, the fuel consumption per unit drawbar power reaches a minimum, and the overall tractive performance is at an optimum.
A study of the adaptive control of spark timing using cylinder pressure in a spark ignition engine
Authors: Cho H , Lee J , Yoo J 
Published: October 2002

Spark timing is one of the major parameters influencing engine performance and emissions. In most of today's automotive spark ignition (SI) engines an electronic control unit controls spark timing based on preset values that are functions of load and speed. In this system, the preset spark timing can be different from the optimum value owing to deviations from mass production, ageing effects and a number of other factors. In the present study, a control logic is investigated for the real-time adaptation of spark timing to the optimal value. The simulation program, including an engineering model for cycle-by-cycle combustion variation, is developed for investigating the spark timing control logic. It has been found that the location of the peak pressure in the cylinder is one of the appropriate parameters used to estimate the optimum spark timing. It is also shown that experimental results reflect the simulation outputs and reasonableness of the spark timing control logic for location of the peak pressure.
A simple analytical model for estimating air leakage through rotary valves
Authors: Rogers J , Bradley M S A , Pittman A N , Farnish R J , Reed A R 
Published: October 2002

This paper presents an analytical model from which to estimate the air leakage through rotary valves feeding positive-pressure pneumatic conveying systems. Estimating air leakage through rotary valves is an important part of the design of certain pneumatic conveying systems. Accounting for leakage assists in estimating blower and bin vent requirements and reduces maintenance costs and downtime. An overestimate of the leakage can contribute to inefficiencies, excessive pipeline wear and particle attrition, while an underestimate can lead to blocked pipelines and severely reduced solid flowrates through the valve. The formulation of the analytical model presented in this paper is based on the principle of air flow through multiple orifice plates in series. The leakage rate across a pressure differential is determined by treating each constriction between rotor blade and casing as an orifice plate. The validity of the model is confirmed by comparing its results to previously recorded empirical data. Note that, while this paper addresses rotary valves feeding positive-pressure pneumatic conveying systems, the same principles can be used for the design of vacuum pneumatic conveying systems. For vacuum systems the air density and differential pressure must be accounted for in order to estimate the air leakage rate in the opposite direction through the valve. Accounting for this type of leakage is especially important for vacuum systems with (a) multiple feed points, in order to ensure that adequate upstream transport velocities are reached, and (b) inert gas as the transport medium, where air leakage into the system can dilute the conveying gas.