Showing papers by "Cranfield University published in 1981"

A general model of spark ignition for gaseous and liquid fuel-air mixtures

Abstract: In a previous publication a model for the spark ignition of heterogeneous fuel-air mixtures is described which assumes that chemical reaction rates are infinitely fast, and that the sole criterion for successful ignition is an adequate concentration of fuel vapor in the ignition zone. In the present study this model is extended to include (1) the effects of finite chemical reaction rates, which are known to be significant for well-atomized fuels at low pressures and low equivalence ratios, and (2) the presence of fuel vapor in the mixture flowing into the ignition zone. Thus, it now has general application to both quiescent and flowing mixtures of air with either gaseous, liquid or evaporated fuel, or any combination of these fuels. The general validity of the new model is demonstrated by a close level of agreement between theoretical predictions of minimum ignition energy and the corresponding experimental values obtained over wide ranges of pressure, velocity, equivalence ratio, mean fuel drop size and fuel volatility. As no experimental data appeared to exist on minimum ignition energies in heterogeneous mixtures of liquid fuel drops and air in the presence of fuel vapor, some new experiments were undertaken to procure such data for both quiescent and flowing mixtures. The results obtained from this program agree closely with the corresponding predicted values, thereby providing additional support for the new model.

Flame propagation in heterogeneous mixtures of fuel droplets, fuel vapor and air

Abstract: A model of flame deflagration is proposed for application to quiescent combustible mixtures in which the fuel is present in the form of a multidroplet mist, or vapor, or both. In order to test the validity of the model, measurements of flame speed are carried out for three different fuels over a range of values of drop size, vapor concentration, equivalence ratio and pressure. Inaccuracies due to buoyancy effects and the settling of fuel, drops are minimized by conducting the flame speed measurements in a vertical tube while it falls freely under the influence of gravity. The accuracy of the data is further improved by incorporating, various acoustic devices into the tube to produce a ‘flat’ flame, instead of the normal semi-ellipsoidal shape. The experimental results of burning velocity show satisfactory agreement with predicted values, thus confirming the basic premise of the model.

Airblast atomization of alternative liquid petroleum fuels under high pressure conditions

Abstract: A study has been conducted of the effects that fuel and air properties have upon the mean droplet size characteristics of a pre-filming airblast atomizer of the type commonly employed in the gas turbine engine The fuels tested included kerosine, gas oil and two blends of gas oil in residual fuel oil The tests were carried out over a wide range of air pressures (about 1 to 13 atmospheres), fuel viscosities (about 0001 to 0037 Ns/sq m) and the spray mean drop sizes were measured using a laser light-scattering technique The experimental data accumulated in the study is presented in the paper and it is concluded that the spray Sauter Mean Diameter performance of the atomizer studied can be predicted to a reasonable degree of accuracy, over the range of conditions studied, by a relatively simple correlating equation

Beyond the Peter Principle—Managing Successful Transitions

Abstract: Laurence J. Peter, in his best selling book, The Peter Principle, argued that individuals are promoted to their level of incompetence. He saw this progression as being typified by successive promotion from success at lower levels until the individual gets to a point where he is described as inefficient. The Peter Principle has been accepted because it described clearly and vividly the experience of individuals and of organisations, but we believe that whilst it is descriptively correct, it is only partially true in its conclusions.

Use of a profilometer for surface mapping

Abstract: The employmnet of stylus profilometry, augmented by computer-based data-handling, is playing an increasing role in surface texture assessment. Such systems provide detailed descriptions of surfaces as well as three-dimensional maps of their inverse—ie with the valleys appearing as peaks and vice versa. This paper describes a new measurement and data processing system and demonstrates the usefulness of the technique by presenting typical results as isometric and contour surface maps

Comparison of J testing techniques and correlation J-COD using structural steel specimens

Abstract: J integral and COD measurements were made simultaneously on three-point bend specimens of 50D structural steel (specification BS4360). Tests were performed at temperatures over the range -100°C up to room temperature, and at each temperature a series of specimens with a/W ranging from 0.2 to 0.8 were tested.

On the L2 nature of solutions of nth order symmetric differential equations and McLeod's conjecture

Abstract: We investigate the integrable square properties of solutions of linear symmetric differential equations of arbitrarily large order 2m, whose coefficients involve a real multiple ɑr of certain positive real powers β of the independent variable x. Information on the L2 nature is obtained by variation of parameters from Meijer function solutions of an associated homogeneous equation of hypergeometric type. When the coefficients of the differential expressions are positive, it is possible, by a suitable choice of ɑr, β and m, to obtain between m and 2m —1 linearly independent solutions in L2(0, ∞). This proves a conjecture of J. B. McLeod that the deficiency index can take values between m and 2m —1 for such operators.

Surface Textures of Annealed AISI 304 Stainless Steel Etched by Aqueous Ferric Chloride—Hydrochloric Acid Solutions

Abstract: SUMMARYIn commercial photoetching, the etchant most commonly used for the production of perforated and recessed piece-parts and components in AISI 304 stainless steel is the FeCl3-HCl-H2O system. It has been shown that the surface texture of the etched steel is strongly dependent on etchant composition and temperature. Optimum etching conditions have been found for achieving both smooth and rough finishes. The important role of the reaction products is also discussed.

Skin Friction and Heat Transfer at an Infinite Swept Attachment Line

Abstract: Simple, yet reasonably accurate, expressions have been developed for the prediction of skin friction and heat transfer coefficient at an infinite swept attachment line using the concepts of ‘reference temperature’ and ‘Reynolds analogy’. The formulae have then been used to investigate the effect of varying sweep angle with constant undisturbed free stream conditions in the limits of very low and very high Mach number.

Intracytoplasmic membranes in oxygen-limited chemostat cultures of Methylosinus trichosporium OB3b: Biocatalytic implications of physiologically balanced growth

Abstract: The continuous culture growth conditions for induction of intracytoplasmic membranes in Methylosinus trichosporium OB3b are described. During oxygen-limited, nitrate-excess chemostat culture, organisms have an extensive intracytoplasmic membrane system and particulate, cell-free methane mono-oxygenase (MMO). Under methane limitation fewer intracytoplasmic membranes are seen, while under all other conditions tested, membranes are absent and cell-free MMO is entirely soluble. These findings may be important in relation to the development of oxidative biotransformation processes using this bacterium.

Dynamic Response of a Double Articulated Offshore Loading Structure to Noncollinear Waves and Current

Abstract: The dynamic response of a double articulated structure to non-collinear Airey waves and a steady current is studied for various waves and varying current directions. The governing equations of motion are derived by Lagrange's method where wave and current forces are computed by a modified form of Morison's equation which takes account of relative motion of water particles with respect to the oscillating structure. The resulting equations are highly non-linear and are solved numerically by using a block integration method. The computed results predict complex whirling oscillations of the structure to non-collinear waves and current. Paper ASME 1977 Summer Applied Mechanics/Bioengineering/Fluids Engineering Conference, Yale University, New Haven Connecticut, U.S.A., June 1977. Starting in 1946 as the College of Aeronautics, the Cranfield Institute of Technology was granted university status in 1969. In 1993 it changed its name to Cranfield University.

Radiation and smoke from the gas turbine combustor using heavy fuels

Abstract: Broadening of aviation fuel specifications has been simulated using blends of gas oil and residual fuel oil. Radiation, smoke and temperature measurements in an experimental combustor at various air pressures, inlet temperatures and air/fuel ratios showed a diminishing rate of increase of radiation with soot concentration, and reduced sensitivity of smoke to fuel hydrogen content at higher combustor pressures. 6 refs.

The Hybrid Diffuser

Abstract: A vortex controlled diffuser has recently been reported [1], which attained high levels of pressure recovery within a short length. This diffuser has, however, achieved only a limited application because of its bleed-off requirements. The present work indicates a means by which this disadvantage can be overcome by using a hybrid arrangement of conventional and vortex controlled diffusers. The outcome was an efficient diffuser, half the length of the equivalent conical diffuser, and which would operate satisfactorily without either bleed-off or vanes projecting into the flow.

The Vibration Isolating Properties of Uncentralized Squeeze-Film Damper Bearings Supporting a Flexible Rotor

Abstract: The ability of an uncentralized squeeze-film damper bearing to inhibit the effects of vibration in a flexible rotor-bearing system, has been assessed in terms of non-dimensional system parameters. This analytical approach has shown that a correctly designed squeeze-film damper bearing is a very effective means of reducing both the amplitude of motion of the rotor and the force transmitted to the bearing support structure. However, the analysis has also indicated that a poorly designed squeeze-film damper bearing can produce amplitudes and forces greater than those which would arise if the bearing support remained rigid. An experimental programme has supported the validity of the above analytical technique by showing that the measured motion orbits of the journal and disk centers as the rotor passes through the critical speed, are very similar to those predicted theoretically. Also, the response curves for specific groups of system parameters show very similar trends in practice, to those which result from the analytical approach. Some indication of the ability of a squeeze-film damper bearing to reduce the effect of much greater unbalance than normal is also reported.

Multi-tool job sequencing for tool-change reduction

Abstract: Statistical analysis of machine utilization has shown that about 45% of machine time is spent in tool changes between jobs. Reducing job change-over costs can therefore make a big difference in machine utilization. Job change-over costs depend greatly on the job sequence chosen for a. given job collection, and this paper shows that systematic job sequencing can reduce machine setting time by as much as 80%. Apart from the direct benefit accruing from systematic job sequencing, there can be indirect benefits through a continuing programme of tool and tooling standardization. The method is available in both a manual version and a computerized version, and a demonstration is given.

Marketing of Continuing Management Development

Abstract: Describes how one university school applied the principles and practices of marketing to short course activities between 1975 and 1979. Reveals that the application afforded good commercial success.

Assessment of Propeller Influence on Lateral-Directional Stability of Multiengine Aircraft

Abstract: Using a twin-engine turboprop aircraft, flight measurements were made to supplement the very limited data on the effects of propellers on the individual lateral static and dynamic stability derivatives. It is found that the propeller slipstream significantly affects the wing contribution to the derivative lv. A significant reduction in recovery time from the spiral mode instability in low-speed, high-power conditions is consequently found. Propeller disk contribution to the overall damping in yaw derivative nr is also found to be significant. Propeller contributions to yv and nv, due to the known "fin" effect, are found to be small for the test aircraft. Existing expressions to calculate propeller influence on lv, nv, and yv are shown to be adequate, while an expression to calculate the propeller contribution to nr, which appears not to have been analyzed before, is presented.

Plastic flow of mild steel (En8) at different strain-rates under abruptly-changing deformation paths

Abstract: Strain-gauged thin-walled tubular specimens of annealed medium carbon steel (En8) were tested at room temperature in combined twisting and extension using a closed-loop, servo-controlled, electro-hydraulic biaxial testing machine. Bilinear deformation paths of twisting at a constant rate followed by extension at three different rates were investigated. Precise measurements of the resulting torque and load, together with the controlled deformation parameters, were recorded as functions of time. This study extends earlier work ( Meguid , Malvern and Campbell , 1979, J. Engng Mater. Technol. 101 , 248) in which a notable feature of this particular type of bilinear testing was reported: namely, that it was possible to obtain almost the entire positive quadrant of the initial yield locus from a single run without unloading or reloading (neutral loading). Here, particular attention has been given to the effect of the axial strain-rate on the shape of these “initial” yield loci. Attention has also been given to the effect of the sudden change of direction in the deformation path upon the deviatoric stress and the plastic strain-rate vectors. The results indicate that there exist appreciable differences between the Mises equivalent stress and equivalent plastic strain curves (up to strains of order 2%) for the three axial strain-rates investigated. These differences are attributed to the rate-sensitivity of the material. The results also show a much slower alignment of the deviatoric stress vector direction to the direction of the plastic strain-rate vector than had been expected. Comparisons with two theoretical analyses of a bilinear deformation path of quasistatic twisting followed by extension at a constant strain-rate are made, one using Perzyna's (1966) viscoplastic constitutive law for rate-sensitive (but non-strainhardening) material and the other using a rate-independent theory. Refinements in the test procedures now reveal that significant differences exist between calculated and measured axial and shear stresses. In contrast, both theories gave reasonably good agreement with the time history of the equivalent stress and the stress trajectory, in agreement with the earlier work.

Programmable Adaptive Control of EDM

Abstract: Three important respects in which the automation of the EDM process can beneficially advance its industrial utilisation are: programmability — for strategic optimisation of real jobs, and job planning. adaptive control — for trouble-free, real-time machine operation and management, leading to: operating independence — making increased time available for the operator to attend to the essential practical tasks which, particularly in toolmaking, require human skill, judgement and ingenuity. The Cranfield PAC-EDM system is discussed in relation to these attributes. Its use on a real industrial EDM job of some complexity and difficulty will be illustrated. The economics of utilisation will also be considered.

The Effect of Mode Interaction in Orthotropic Fibre Reinforced Composite Plain Channel Section Columns

Abstract: A theoretical investigation into the interactive buckling behaviour of thin- walled orthotropic plain channel section columns is presented. A semi-energy method of analysis is used and the effects of local buckling in all elements of the section are taken into consideration. Changes in the locally buckled form after buckling are taken into account in an approximate manner and the effects of local and overall imperfections are also considered. In the paper particular attention is paid to the analysis of columns with coincident local and Euler buckling loads, since these columns exhibit unstable post-buckling equilibrium behaviour and due to this are highly sensitive to geometrical imperfections.