Measured Pressure Data Research Articles

Modelling Spatial Radiative Heat Flux Distribution in a Direct Injection Diesel Engine

In this paper, the spatial distribution of radiative heat flux from a luminous flame to various positions on the cylinder head of a direct injection diesel engine is modelled and the results compared with some published experimental investigations. The model is primarily based on measured pressure data, which are converted into fuel-burned rate data through a single-zone heat-release rate analysis. Coupled with appropriate soot formation and oxidation models, the fuel-burned rate data are converted into the soot contents in the cylinder. By separating the combustion chamber into a burned zone and an unburned zone, the radiation temperature, the absorption coefficient and the spatial distribution of radiative heat flux to the cylinder walls are calculated.

Origin of Subpressure and Hydrocarbon Exploration in Shiwu Fault Depression, Songliao Basin, China: ABSTRACT

In the Shiwu fault depression, evolutionary history of formation pressure can be deduced on the basis of structural evolutionary history. Uplifting and denudation caused high pressure to evolve into low pressure. The main factors controlling the evolutions are (1) generation of fractures and release of high pressure, (2) temperature reduction and water-cooling pressure reduction, (3) desaturation and gas dissociation, and (4) diffusion and dissipation of gas. According to the pressure evolutionary history, the study area has had two pool-forming stages. During uplifting and denudation, fracture generation, and the transformation from high pressure to low pressure, the protogenic high-pressure oil and gas pools were transformed into low-pressure relic pools, and secondary pools with normal pressure formed above them. A predictor equation of the low pressure has been proposed on the basis of the balanced depth in the undercompaction zone, as well as the eroded thickness of the overlying strata. According to this equation, measured pressure data, well logs, and seismic interval velocity data, pressure prediction has been made in the study area by drawing on experience gained at key points. In the light of pressure evolutionary history and pool-forming history, it is regarded that the exploration potential of the low-pressure zonemore » is not as good as that of the hydrostatic-pressure zone. This has been verified by petroleum exploration activities.« less

Application of a wave transform to pressure transient testing in porous media

Solutions to the diffusion equation for nonuniform media are difficult to obtain in a form that can be easily evaluated. Often the solutions are written as the inverse Laplace transform of an inverse Fourier transform. In this paper, I show that the wave transform of Bragg and Dettman (1968) coupled with the Cagniard-de Hoop method for solving the wave propagation problem results in simplified solutions to the problem of pressure transient testing in linear composite reservoirs. The potential usefulness of an inverse wave transform, which would transform measured pressure data (smooth) into a wave signal propagating at the ‘velocity’ of the square root of the diffusivity, is demonstrated by a synthetic example. In the example, diffusivity of the source region is estimated from the ‘time’ of the direct wave arrival, while diffusivity of a second, higher diffusivity region is estimated from the ‘velocity’ of the head wave. In the wave domain the time-like variable has units of (time)1/2 which makes the units of ‘velocity’ equal to L T-(1/2). I also demonstrate, using synthetic data, that it is difficult, but perhaps possible, to invert the wave transform numerically.

Heat Release Analysis of Oxygen-Enriched Diesel Combustion

A heat release correlation for oxygen-enriched diesel combustion is being developed through heat release analysis of cylinder pressure data from a single-cylinder diesel engine operating under various levels of oxygen enrichment. Results show that standard combustion correlations available in the literature do not accurately describe oxygen-enriched diesel combustion. A novel functional form is therefore proposed, which is shown to reproduce measured heat release profiles closely, under different operating conditions and levels of oxygen enrichment. The mathematical complexity of the associated curve-fitting problem is maintained at the same level of difficulty as for standard correlations. When the novel correlation is incorporated into a computer simulation of diesel engine operation with oxygen enrichment, the latter predicts pressure traces in excellent agreement with measured pressure data. This demonstrates the potential of the proposed combustion simulation to guide the application of oxygen-enriched technology successfully to a variety of multicylinder diesel systems.

Phasing cylinder pressure to crank angle in a direct injection diesel engine, by simulation of compression curve and elaboration of measured pressure data

When measurements of indicator diagrams are made in an internal combustion engine, the serious problem arises of accurate phasing of pressure data to crank position. This work presents a novel thermodynamic method for such a phasing. A measuring assembly consisting of a piezoelectric transducer, a charge amplifier and a fast data acquisition board installed on a compatible PC computer, is used to obtain the indicator diagrams (i.e. pairs of pressure-time), dispensing thus with the use of a signal from the flywheel TDC marker. An advanced simulation thermodynamic model for the corresponding compression curve (i.e. before fuel injection) is proposed, which includes a detailed zero dimensional energy cascade turbulence submodel for predicting the heat transfer rate between cylinder gas and walls, a blowby rate submodel containing flow calculations in the piston ring pack assembly passages under rings motion conditions, and properties-relations pertaining to real gas (air) behaviour. The measured pressure data are corrected for drift and their exact period (from cycle to cycle) is determined. The theoretical compression curve is shifted (in time) to “coincide” to the compression part (before fuel injection) of the first measured cycle, so that its TDC is determined. The coincidence of the two compression curves is continuously (iteratively) improved by using a double iteration procedure, i.e. by firstly shifting the curves in time and secondly by varying the model’s parameters and calibration constants. After this step, the phasing of pressure data to crank angle of the following cycles can be easily determined, since the corresponding time periods are already accurately calculated. The method is applied with success, under various speed and load conditions, for a fully instrumented single cylinder, LISTER LV1, direct injection, naturally aspirated, Diesel engine installation at the authors’ laboratory.

An Approach to Unsteady Flow Rate Measurement Utilizing Dynamic Characteristics between Pressure and Flow Rate along a Pipeline. A Method Using Pressures at Two Separated Points.

The paper describes an approach to estimating unsteady flow rate through a pipe in real time. In this method, the unsteady flow rate is estimated by using hydraulic pipeline dynamics, and measured pressures at two points (upstream and downstream section) distant by a finite length along the pipeline. By scheming the high-speed operations of convolutions between the weighting functions and measured pressure data, data processing in a microcomputer system is achieved in real time using exclusive precalculated maps. The weighting functions are obtained by the application of the inverse fast Fourier transform from the transfer functions which are derived from the transfer matrix. Under unsteady laminar oil flow, good agreement between the estimated and measured flow rate waveforms illustrates the validity of the method proposed here.

Simulated Mini-Frac Analysis

Abstract A new mini-frac methodology is presented for the automated simulation of mini-frac analysis. The solution is based on solving the governing momentum, mass conservation and constitutive relationships for Perkins-Kern/Nordgren (PKN), Geertsma-Deklerk (ODK) and penny-shaped type fracture geometries. The analytical technique is unique because the fracture propagation characteristics of length, width, pressure and efficiency are numerically calculated from conservation of momentum and mass principles for power-law type fluids. Major enhancements to current mini-frac analysis include:momentum and mass conservation,spurt loss,fluid flow-back after pumping,time-dependent fluid loss coefficients,interference closure, anddetermination of formation permeability. The analysis has the additional advantage of using the measured pressure decline data as a history matching parameter to determine the appropriate fracture model and sensitivity of input data. A number of mini-frac designs, parametric studies and field case examples are presented to illustrate the applicability of the numerical technique. Introduction Mini-frac analysis provides a method of estimating fracture dimensions, efficiency and leak-off coefficients prior to designing a full-scale fracture treatment. Mini-frac analyses as originally formulated by Nolte(1, 2) quantify the fracturing process as estimated from the measured pressure decline data. Most mini-frac analyses are based on Nolte's equations and do not account for the effects of fluid rheology or momentum conservation. The measured pressure data is simply used in place of solving the momentum equation. Neglecting momentum can result in unrealistic estimations of fracture characteristics and fluid leak-off coefficients for the design fracture and geometry models. Currently, only the width-opening pressure relationship and pressure decline data are used to estimate mini-frac characteristics. Lee(3) has recently improved upon this by including Biot's energy balance equation for GDK-type fractures. To the authors' knowledge, the energy method has not been applied to PKN or penny-shaped type fracture geometries. The energy balance method does eliminate some of the anomalies in mini-frac analysis. However, this method does not fully account for viscous-driven fractures. A new mini-frac methodology is reported as formulated from conservation of mass and momentum for power-law type fluids. The methodology utilizes the same fracture propagation equations-of-state as used in the design simulator. The solution technique can be implemented with any hydraulic fracturing simulator and will provide results compatible with the design fracture treatment. This analysis does not assume the fracture width is proportional to the measured pressure. Instead, the governing mass and momentum equations are coupled with the measured closure time to predict fracture propagation characteristics. From the numerically simulated fracture geometries, pressures, efficiencies and leak-off coefficients, the analyst can determine which fracture model more closely represents the measured pressure response and formation permeability. The main advantage of this mini-frac technique is that mass and momentum are both satisfied. Additionally, the important effects of flow-back, interference closure, time.::dependent leakoff and fluid rheology are simulated. The numerical results are used in conjunction with the measured pressure decline data to history match such input characteristics as fracture height, pay zone height, Young's modulus and spurt loss.

Force and pressure study of thick cambered/twisted 58 deg delta wings

This paper summarizes the results of a force, moment, and pressure experiment involving six thick, cambered and twisted, delta wings with 58 deg leading-edge sweep. The goal of this study was to determine a configuration that was self-trimming at a design lift coefficient of 0.25 and Mach number of 0.80. Analysis of the forces and moments data did not indicate a configuration that satisfied the design constraints; however, the configuration that came closest and had the best overall performance was selected for detailed pressure study. Wing pressure data and limited surface oil-flow photographs for this configuration showed attached flow at the design point. The associated inviscid forces and moments solutions from the Vortex Lattice Method-Suction Analogy, PAN AIR, FLO-28, and FLO-57 were compared with experimental data and showed varying levels of success. The computed pressures obtained from the PAN AIR, FLO-28, and FLO-57 for an angle of attack of 6.08 deg underpredicted the measured upper-surface pressure peak. At higher angles of attack, the lower-surface theoretical and measured pressure data compared well, whereas the upper-surface pressure predictions only approximated the trends but not the pressure level. Of the three codes, the PAN AIR is shown to be the best overall predictor.

Acoustic power measurement for single and annular stream duct-nozzle systems utilizing a modal decomposition scheme

A refined acoustic impulse technique was used to evaluate the adequacy of single point in-duct pressure measurements for determining the acoustic power for incident, reflected, and transmitted fields for single and annular stream duct-nozzle systems at various flow conditions. The spatial distributions of incident and reflected pressure fields were measured at several radial and azimuthal locations inside the duct. A modal decomposition scheme was used to derive the acoustic power of each duct mode from the complex pressure measurements. The total sums of these individual modal acoustic powers were compared with the area-weighted acoustic power distributions that were evaluated from measured pressure data. It was found that a single-point measurement near the duct wall is adequate for estimating the transmitted power for both single and annular stream duct-nozzle systems.

Polymer Melt Rheological Property Measurement in a Novel Composite-Geometry Flow Rheometer

A novel rheometer is described, in which extensional viscosity and elastic shear compliance are determined simultaneously from pressure measurements taken on steady state polymer melt flows through an open-ended die with successive, similarly shaped, converging and diverging zones. Equations incorporating practically realistic simplifying approximations are developed for the calculation of extensional viscosity and shear compliance from the measured pressure data. The construction of a prototype rheometer is described, and results from its operation are presented. Agreement between these results and published melt elasticity data for a low-density polyethylene material gives evidence to confirm the basic rheometric principle and flow analysis. The implications of pressure measurement errors are discussed. Assembly of the new composite-geometry rheometer in series with a conventional capillary viscometer would give in-line shear viscosity characterization simultaneously and facilitate on-line processing of pressure data from the converging and diverging flows by microcomputer to provide complete characterizations for practical use in polymer process machinery design. The work represents a significant advance on the basic empirical power law modelling process used for many years by practising engineers to represent shear viscosity phenomena as a basis for design. No other methodology is currently available to suit the engineer.

Aylesbury and ACE: Some interesting findings

This paper summarizes the major findings of an in-depth study [1] of wind pressures on the Aylesbury experimental house. The scope of the study includes part of the Aylesbury Collaborative Experiment (ACE), a detailed examination of the full scale pressure data, and various comparisons between model scale data; namely, between new 1:100 and 1:500 scale tests at UWO, between current and previous data obtained by the authors [2,3], and between the UWO 1:100 scale data and pressure data obtained from 1:100 scale model tests from three other wind tunnel laboratories. The results of the study indicate that much of the mean pressure data obtained at full scale are subject to reference static pressure errors, but the corresponding fluctuating pressures are reliable and agree well with model scale in most instances. The comparison of pressure data obtained from the different laboratories indicates that significant differences in the measured pressure data occur even though identical models are used.

Computer simulation for combustion and exhaust emissions in spark ignition engine

In order to predict the exhaust emission concentration without any measured pressure data or empirical burned mass fraction, a new method of combustion simulation was developed. It consists of two major parts: A flame propagation model, and an emission formation model. The flame propagation model, which is based on the burning velocity of the gaseous mixture, gives the pressure and temperature history in the cylinder and in the burned mass fraction for various parameters. In this model, the flame was assumed to propagate across the combustion cylinder as a spherical front centered around a spark plug; a heterogenous temperature field and uniform pressure in the cylinder were assumed. The cylinder consists, of unburned gas and numerous elements of burned gas which burned during successive small increments, of the crank angle. Using various values obtained with the flame propagation model, emission concentration were calculated in individual elements of burned gas, assuming partial equilibrium. Eleven chemical species were taken into consideration. Nine species, other than N and NO, were assumed to be equal to the equilibrium concentration throughout the time of interest. The formation of NO was assumed to be a nonequilibrium process controlled by chemical kinetics and to take place only in the post flame. Computer simulation developed here gives results consistent with the experimental data and it may be utilized for the practical design of a spark ignition engine.