bluuebunny/crossref_metadata_2025 huggingface dataset:
A New Computational Model for Expiratory Flow From Nonhomogeneous Human Lungs
Authors: Lambert R. K.
Published: June 2009

A model has been developed for expiration from human lungs in which the mechanical properties of the airways and parenchyma can be varied between regions. The model is based on an existing homogeneous model. The fluid mechanical problem of the merging of dissimilar flows from adjacent regions is underspecified by the conservation laws of mass and energy. An existing, empirically derived result, provides the required extra equation. Model simulation of a nonhomogeneously distributed mild constriction of the peripheral airways gives results for maximal flows and alveolar pressure differences which are in good agreement with recent experimental findings.
Steady Flow Through a Double Converging-Diverging Tube Model for Mild Coronary Stenoses
Authors: van Dreumel S. C. , Kuiken G. D. C.
Published: June 2009

Velocity profiles and the pressure drop across two mild (62 percent) coronary stenoses in series have been investigated numerically and experimentally in a perspex-tube model. The mean flow rate was varied to correspond to a Reynolds number range of 50–400. The pressure drop across two identical (62 percent) stenoses show that for low Reynolds numbers the total effect of two stenoses equals that of two single stenoses. A reduction of 10 percent is found for the higher Reynolds numbers investigated. Numerical and experimental results obtained for the velocity profiles agree very well. The effect of varying the converging angle of a single mild (62 percent) coronary stenosis on the fluid flow has been determined numerically using a finite element method. Pressure-flow relation, especially with respect to relative short stenoses, is discussed.
Effect of Tilting Disk, Heart Valve Orientation on Flow Through a Curved Aortic Model
Authors: Walker J. D. , Tiederman W. G. , Phillips W. M.
Published: June 2009

The influence of tilting disk valve orientation on pulsatile flow through a curved tube model of the human aorta was studied. Simultaneous, two-component laser Doppler velocimeter measurements were made in a tube having a 22 mm diameter and 41 mm radius of curvature which simulated the average dimensions of the adult aorta. The blood analog fluid had a viscosity of 3.0 cp and matched the refractive index of the glass model aorta. Results at mid-arch showed low turbulence levels in early systole and no influence of valve orientation. During mid-systole, fluid from the ventricle reached mid-arch exhibiting strong influence of valve orientation and increased turbulence levels. With the major orifice of the valve adjacent to the inner curved wall, the peak turbulent shear stress was 307 dynes/cm2 at mid-arch during mid-systole. When the major orifice was rotated 180 degrees, the peak value was reduced to 91 dynes/cm2 at the same location and time. At the exit of the curved section, the flow was independent of the valve orientation and the turbulent shear stress levels were an order of magnitude lower than the peak value at the inlet. This study demonstrated that orienting the major orifice of a tilting disk valve adjacent to the outer curved wall minimized turbulent shear stress levels.
Biomechanical Evaluation of the Axial Compressive Responses of the Human Cadaveric and Manikin Necks
Authors: Yoganandan N. , Sances A. , Pintar F.
Published: June 2009

Cervical spine injuries such as wedge, burst, and tear drop fractures are often associated with compressive axial loads delivered to the human head-neck complex. Understanding the injury mechanisms, the kinematics of the anatomic structure, and the tissue tolerances can improve clinical prognosis and facilitate a better design for anthropomorphic devices. The axial compressive response of human cadaveric preparations was compared with the 50th percentile anthropomorphic Hybrid III manikin under various loading rates. Ten fresh human cadavers were used in the study. Intact cadaver torsos, head-cervical spines, and ligamentous cervical columns were tested. The head-neck structure and the neck (without head) of the Hybrid III manikin were also tested. Responses of the human cadaveric preparations and manikin structures were nonlinear at all rates of loading. However, axial stiffness, a measure of the ability of the structure to withstand external force, was higher under all rates of loading for manikin preparations when compared with the human cadaveric tissues.
Yield Behavior of Bovine Cancellous Bone
Authors: Turner C. H.
Published: June 2009

The compressive yield strain was measured for 61 specimens of bovine cancellous bone from three distal femora. There was no significant relationship (p = 0.08, R2 = 0.051) between yield strain and the degree of trabecular orientation. There was a significant positive correlation (p<0.00001, R2 = 0.319) between yield strain and structural (apparent) density and significant negative correlation (p<0.0025, R2 = 0.145) between yield strain and bone density. Yield strain correlated best with bone solid volume fraction Vv (εy = 0.592 + 1.446vv, R2 = 0.337). The quantity, yield strain, is highly dependent on specific definitions of the yield point and the point of zero strain. For this study the yield point was defined by a 0.0003 offset criterion, and the point of zero strain was defined as the point where the tangent at 15 percent of yield crosses zero. The results using these definitions were compared with results using yield strain values determined by other definitions of the yield point and zero strain. The correlations between yield strain and trabecular orientation, structural density and bone density changed very little for differing definitions of yield. The results suggest that yield strain in cancellous bone is isotropic or independent of textural anisotropy, so the yield behavior may be characterized by a maximum strain yield criterion. The results also suggest that the primary mode of yield in cancellous bone is buckling of the trabeculae.
A New Design of Vehicle Seat Intended to Alleviate Lower Back Pain
Authors: Johnson D. A. , Samin J. C. , Neve M.
Published: June 2009

The novelty in the proposed seat design consists in allowing a free vertical motion of the back rest, so as to decrease the strain on the spinal column. Road and vibrating table tests show that the strain is indeed considerably reduced. A simple mathematical model of the seated human body provides a qualitative explanation of this improvement.
The Matching of Thermal Fields Surrounding Countercurrent Microvessels and the Closure Approximation in the Weinbaum-Jiji Equation
Authors: Weinbaum S. , Jiji L. M.
Published: June 2009

A second order perturbation theory is developed to show the difference between the average artery-vein temperature Tm and the local average tissue temperature θ. This theory demonstrates that the closure approximation in the Weinbaum-Jiji bioheat equation does not require that θ = Tm and that although the difference between these two temperatures is second order the magnitude of the countercurrent convection terms in the Weibaum-Jiji equation can be of order unity. The theory also shows that to second order this new bioheat equation is the same as the simplified set of one-dimensional model equations used in Baish et al. [5].
A Technique for Measuring the Thermal Conductivity and Evaluating the “Apparent Conductivity” Concept in Biomaterials
Authors: Arkin H. , Holmes K. R. , Chen M. M.
Published: June 2009

A simple technique for measuring thermal conductivity of biomaterials is described. The method is based on depositing a pulse of heat into the material of choice, and fitting the subsequent local temperature decay to that predicted by a theoretical model. This transient method is most suitable in situations where frequent measurements of the thermal conductivity are desired. The method was evaluated by calculating the thermal conductivity of several inert materials. The measured conductivities compared well with published values. The developed technique was also used to examine the applicability of the “apparent conductivity” index to combine both conductive and blood-convective thermal effects in living, blood perfused tissues. Using both simulated and experimental results, it was shown that the changes in the apparent conductivity are highly correlated with changes in blood flow. However, quantitative application of this index must be restricted to conditions that are similar to those which existed at the time the apparent conductivity was measured.
Design and Development of a Micro-Thermocouple Sensor for Determining Temperature and Relative Humidity Patterns Within an Airstream
Authors: Eisner A. D. , Martonen T. B.
Published: June 2009

This paper describes the production and calibration of a miniature psychrometer treated with a specially developed porous coating. The investigation was conducted to determine localized patterns of rapidly changing temperature and relative humidity in dynamic flowing gas environments (e.g., with particular attention to future applications to the human respiratory system). The technique involved the use of dry miniature thermocouples and wetted miniature thermocouples coated with boron nitride to act as a wicking material. A precision humidity generator was developed for calibrating the psychrometer. It was found that, in most cases, the measured and expected (i.e., theoretically predicted) relative humidity agreed to within 0.5 to 1.0 percent relative humidity. Procedures that would decrease this discrepancy even further were pinpointed, and advantages of using the miniature psychrometer were assessed.
The Mechanism of Mucus Clearance in Cough
Authors: Basser P. J. , McMahon T. A. , Griffith P.
Published: June 2009

An instability resembling an avalanche is proposed as the mechanism by which mucus is expelled from the respiratory tract during cough. The cough event was simulated in a model airway. In these experiments, air was forced through a channel whose walls were lined with a non-Newtonian material rheologically similar to tracheal mucus. Frames from high-speed cine photographs showed an unstable event which began as an undulation of the free surface and progressed to a catastrophic clearance of the channel. Measurements of the longitudinal pressure gradient support the hypothesis that the clearance event is initiated when the total stress applied to the mucus analog exceeds its finite yield stress. A continuum model predicts that yielding occurs within the bottom layers of the mucus analog. Calculations based upon estimates of tracheal geometry and air flow show that the clearance event studied here would be expected to occur during a cough but not during normal breathing. Experiments also show that a lubricant introduced between the channel walls and the mucus blanket can reduce the air flow rate required to precipitate the clearance.
An In Vitro Comparative Study of St. Jude Medical and Edwards-Duromedics Bileaflet Valves Using Laser Anemometry
Authors: Fatemi R. , Chandran K. B.
Published: June 2009

An in vitro comparative study of St. Jude (SJ) and Edwards-Duromedics (DM) Bileaflet valves was performed under steady and physiological pulsatile flow conditions in an axisymmetric chamber using Laser Doppler Anemometry (LDA). LDA measurements were conducted in two different orientations; in the first orientation, the LDA traverse was perpendicular and, in the second orientation, parallel to the tilt axis of the leaflets. The axial velocities were measured in both orientations at two different locations distal to the valves. The velocity profiles at peak systole show the presence of stronger vortex in the sinus region for flow past SJ valve in the first orientation compared to the DM valve. Velocity profile distal to the SJ valve in second orientation was relatively flat where as for the DM valve, a jet-like flow was present. The differences found in the velocity profiles between the two valves can be attributed to the differences in geometry with thicker leaflets, smaller angle of leaflets opening and the presence of the leaflet curvature for the DM valve. The results obtained in this study do not show any fluid dynamic advantages due to the curved leaflet geometry of the DM valve.
Relationship Between Hypertension, Hypertrophy, and Opening Angle of Zero-Stress State of Arteries Following Aortic Constriction
Authors: Liu S. Q. , Fung Y. C.
Published: June 2009

Examination of changes occurring in the zero-stress state of an organ provides a way to study cellular growth in the organ due to change of physical stresses. The zero-stress state of the aorta is not a tube. It is a sector with an opening angle that varies with the location on the aorta and changes with cellular remodeling. Blood vessel remodeling can be induced by imposing a constriction on the abdominal aorta by a metal clip (aortic banding), which causes an increase of blood pressure, hypertrophy of the aortic wall, and large change of opening angle. The correlation of the opening angle with the blood vessel wall thickness and blood pressure changes in rat’s aorta due to aortic banding is presented in this report. The opening angle changes daily following the aortic banding. Blood pressure rises in vessels of the upper body, but that in the lower body decreases at first and then rises to an asymptotic value. Blood vessel wall thickness increases in rough proportion to blood pressure. Vessel diameter changes also. But the most dramatic is the course of change of the zero-stress state. Typically, the time to reach 50 percent of asymptotic hypertrophy of blood vessel wall thickness is about 3–5 days. The corresponding time for blood pressure is about 7 days. The opening angle of the zero-stress state, however, increases rapidly at first, reaches a peak in about 2 to 4 days, then decreases gradually to a reduced asymptote. The exact values of the time constants depend on the location along the aortic tree. In general, the course of change of residual strain is very different from those of the blood pressure and the blood vessel wall thickness.
A Model for the Relationship Between the Arterial Pressure and the Heart Period
Authors: Iacovelli F. , Napolitano M. , Federici A. , Sorrentino G.
Published: June 2009

This paper provides a simple model for predicting the relationship between steadystate heart rate and arterial blood pressure. Two current state-of-the-art models of the cardiovascular system as a pump operating in its circuit are reformulated and combined in order to highlight the role of the duration of the heart cycle. The proposed model establishes that the cardiac cycle lengthens linearly with the inverse of the average blood pressure. Experimental data are reported for sixteen preoperated conscious dogs resting quietly on their sides. Vagal and sympathetic blocks have been produced in four dogs in order to obtain a wide range of sympathetic and parasympathetic tones, namely, to cover the entire range of physiological values of the heart rate. For these dogs a comparison between the experimental values and the theoretical predictions shows a good agreement, the results of the linear regression model being statistically significant at the p = 0.001 level for three dogs and at the p = 0.01 level for the fourth dog.
Description and Analysis of a One-Dimensional Gas-Dynamic Model With Independent Time Discretization
Authors: Galindo Jose , Serrano Jose R. , Arnau Francisco J. , Piqueras Pedro
Published: June 2009

Modeling has become an essential technique in design and optimization processes of internal combustion engines. As a consequence, the development of accurate modeling tools is, in this moment, an important research topic. In this paper, a gas-dynamics modeling tool is presented. The model is able to reproduce the global behavior of complete engines. Besides, it is able to calculate different components of the engine individually like the turbocharger, the intercooler, the catalyst, the cylinders or the diesel particulate filter. Finally, the paper emphasizes an innovative feature: the independent time discretization of ducts. It is well known that 1-D models solve the flow through the duct by means of finite difference methods in which a stability requirement limits the time step depending on the mesh size. Thus, the use of small ducts in some parts of the engine reduces the speed of the calculation. The model presented solves this limitation due to the independent calculation for each element. The different elements of the engine are calculate following their own stability criterion and a global manager of the model interconnects them. This new structure provides time saving of up to 50% depending on the engine configuration.
Low Temperature Combustion Using Nitrogen Enrichment to Mitigate NOx From Large Bore Gas-Fueled Engines
Authors: Biruduganti Munidhar S. , Gupta Sreenath B. , Sekar Raj
Published: June 2009

Low Temperature Combustion (LTC) is identified as one of the pathways to meet the mandatory ultra low NOx emissions levels set by regulatory agencies. This phenomenon can be realized by utilizing various advanced combustion control strategies. The present work discusses nitrogen enrichment using an Air Separation Membrane (ASM) as a better alternative to the mature Exhaust Gas Re-circulation (EGR) technique currently in use. A 70% NOx reduction was realized with a moderate 2% nitrogen enrichment while maintaining power density and simultaneously improving Fuel Conversion Efficiency (FCE). The maximum acceptable Nitrogen Enriched Air (NEA) in a single cylinder spark ignited natural gas engine was investigated in this paper. Any enrichment beyond this level degraded engine performance both in terms of power density and FCE, and unburned hydrocarbon (UHC) emissions. The effect of ignition timing was also studied with and without N2 enrichment. Finally, lean burn versus stoichiometric operation utilizing NEA was compared. Analysis showed that lean burn operation along with NEA is one of the effective pathways for realizing better FCE and lower NOx emissions.
Controlling n-Heptane HCCI Combustion With Partial Reforming: Experimental Results and Modeling Analysis
Authors: Hosseini Vahid , Neill W. Stuart , Checkel M. David
Published: June 2009

One potential method for controlling the combustion phasing of a Homogeneous Charge Compression Ignition (HCCI) engine is to vary the fuel chemistry using two fuels with different auto-ignition characteristics. Although a dual-fuel engine concept is technically feasible with current engine management and fuel delivery system technologies, this is not generally seen as a practical solution due to the necessity of supplying and storing two fuels. Onboard partial reforming of a hydrocarbon fuel is seen to be a more attractive way to realize a dual-fuel concept while relying on only one fuel supply infrastructure. Reformer Gas (RG) is a mixture of light gases dominated by hydrogen and carbon monoxide that can be produced from any hydrocarbon fuel using an onboard fuel processor. RG has a high resistance to auto-ignition and wide flammability limits. The ratio of H2 to CO produced depends on the reforming method and conditions, as well as the hydrocarbon fuel. In this study, a CFR engine was operated in HCCI mode at elevated intake air temperatures and pressures. n-heptane was used as the hydrocarbon blending component because of its high cetane number and well-known fuel chemistry. RG was used as the low cetane blending component to retard the combustion phasing. Other influential parameters such as air/fuel ratio, EGR, and intake temperature were maintained constant. The experimental results show that increasing the RG fraction retards the combustion phasing to a more optimized value causing indicated power and fuel conversion efficiency to increase. RG reduced the first stage of heat release, extended the negative temperature coefficient delay period, and retarded the main stage of combustion. Two extreme cases of RG composition with H2/CO ratios of 3/1 and 1/1 were investigated. The results show that both RG compositions retard the combustion phasing, but that the higher hydrogen fraction RG is more effective. A single-zone model with detailed chemical kinetics was used to interpret the experimental results. The effect of RG on combustion phasing retardation was confirmed. It was found that the low temperature heat release was inhibited by a reduction of intermediate radical mole fractions during low temperature reactions and the early stages of the negative temperature coefficient delay period.
Locomotive Exhaust Temperatures During High Altitude Tunnel Operation in Donner Pass
Authors: McDonald Joseph , Nelson Brian , Olson Brian , Iden Michael E. , Fritz Steven G. , Honc Randell L.
Published: June 2009

Locomotives in heavy-haul service at high altitude and within unventilated tunnels operate under some of the most extreme conditions encountered in the U.S. with regard to high ambient temperatures and high locomotive exhaust temperatures. Consideration of such conditions is crucial to the design of future catalytic emission control systems for locomotives. Field testing was conducted on two locomotives certified to U.S. Federal Tier 2 locomotive emissions standards operating as part of a four-locomotive consist pulling a heavy-freight train west-bound through the Donner Pass Region in late August 2007. The highest post-turbine exhaust temperatures observed over the entire test route occurred within Union Pacific Tunnel 41 — an approximately two-mile-long, unventilated tunnel located near Norden, California. Engine protection measures within the electronic locomotive and engine management systems of both locomotives limited the peak exhaust temperatures encountered during the tests to less than 560°C.
Analysis and Customization of Rocker Arm Joint Sliding Velocity
Authors: Geist Bruce K. , Eovaldi David
Published: June 2009

This paper examines how the sliding motion between a rocker arm and valve stem tip can be adjusted by reshaping the rocker pad surface. The valve tip is assumed flat, and the rocker arm and valve stem are assumed to lie in a common plane. It is shown that the rubbing velocity between a rocker arm and valve stem tip, as well as the curvature of the rocker arm pad, may be determined from two features of the contact: 1) the contact point path between rocker arm and valve stem tip and 2) the angle that the valve stem tip makes with the line connecting the rocker pivot to the zero-lift point of contact. An algorithm is presented for determining a rocker arm surface from a prescribed contact point path and valve angle. The derived technique enables customization of rocker arm pad curvature and rocker arm joint sliding velocity.
Locomotive Idle and Start-Up Exhaust Emissions Testing
Authors: Hedrick John C. , Fritz Steven G.
Published: June 2009

The objective of this project was to quantify locomotive idle and start-up emissions, to answer the question: “At what point is it preferable from an emissions standpoint to idle a locomotive engine rather than shut down the engine and restart it when needed?” Idle and restart emissions tests were performed on two Tier 0 emission locomotives; a 1,120 kW EMD MP15-DC Switcher (UPY1378) and a 3,280 kW line-haul GE Dash9-44CW (BNSF4373). The results of the testing showed that continuous idling emissions of NOx and PM were greater than the start up emissions from the two test locomotives. The only exception was the 15-minute restart on the line haul locomotive BNSF4373, but this was envisioned to be due to a non-typical operational cycle of the GE AESS. The results of the extended idle tests showed that the older locomotive (UPY1378) operates at a relatively consistent idle emissions output through the four hours of extended idle. However, idle emissions from BNSF4373 varied over the idle period as the engine speed changes in response to on-board computer controls to accomplish engine warm-up and a series of other locomotive functions.
Application of a Phenomenological Soot Model for Diesel Engine Combustion
Authors: Cheng Xiaobei , Jv Hongling , Wu Yifeng
Published: June 2009

The application of the improved CFD code for the simulation of combustion and emission formation in a high-speed diesel engine has been presented and discussed. The soot concentration transport equation is found and solved together with all other flow equations. A slip correction factor is introduced into this equation. In turbulent combustion, the soot particles are contained within the turbulent eddies, and burnt up swiftly with the dissipation of these eddies in the soot oxidation zone. However, the chemical reactions always process except the dissipation of turbulent eddies and the intermixing of soot particles and turbulent eddies. The soot oxidation rate should be controlled simultaneity by the chemical reactions rate and the dissipation rate of turbulent eddies. A hybrid particle turbulent transport controlled rate and soot oxidation rate model is present in this paper and Soot formation and oxidation processes have been modeled according to this model. A reasonable agreement of the measured and computed data of in-cylinder pressure, soot, and NO emissions for different engine operation conditions has been made. The precision of simulated soot concentration is improved compare with the commonly Hiroyasu—Nagel—Strickland (HNS) soot model.
Authenticating Turbocharger Performance Utilizing ASME PTC-10 Correction Methods
Authors: Shultz Jacque , Chapman Kirby
Published: June 2009

Continued regulatory pressure necessitates the use of precisely designed turbochargers to create the design trapped equivalence ratio within large-bore stationary engines used in the natural gas transmission industry. The upgraded turbochargers scavenge the exhaust gases from the cylinder, and create the air manifold pressure and backpressure on the engine necessary to achieve a specific trapped mass. This combination serves to achieve the emissions reduction required by regulatory agencies. Many engine owner/operators request that an upgraded turbocharger be tested prior to installing the turbocharger on the engine. The purpose of the test is to prevent field hardware iterations that are oftentimes necessary for the turbocharger to meet the air specification on the particular engine. Reworking a turbocharger due to not meeting the airflow and pressure requirement for emissions purposes can be quite costly and in many cases easily discovered through test-cell performance testing. Confirming the as-built turbocharger design specification prior to transporting the turbocharger to the field can decrease downtime and installation costs. There are, however, technical challenges that must be overcome to compare test-cell data to field conditions. This paper discusses the corrections that must be made to the test-cell data in order to determine how the turbocharger will perform on the engine. As the litmus test of the new testing system, performance data is corrected to site conditions verifying the air specification as designed by the end user. The correction method utilized herein is the ASME Power Test Code 10 (PTC-10) version 1997. Performance test data and the compressor map are corrected with the PTC-10 method to field conditions verifying turbocharger site performance before installation. After installation, data collected from the turbocharger operating on engine is compared with test corrected data, authenticating the turbocharger testing system and correction methods.
Analysis of the Relationship Between Mean Indicated Torque and Its Waveform for Modern Common Rail Diesel and Gasoline Engines
Authors: Ponti Fabrizio , Rinaldi Matteo
Published: June 2009

The paper presents the progresses made for the development of a methodology useful for torque estimation, necessary in modern management strategies in order to obtain an indication of the torque produced by the engine. The model developed allows estimating mean indicated torque, cylinder by cylinder, based on instantaneous engine speed fluctuations. The speed signal is picked up directly from the sensor facing the toothed wheel mounted on the engine for control purposes. The engine speed fluctuation amplitudes depend in fact on the combustion and the amount of torque that is being delivered by each cylinder. It is easy to understand therefore how these two quantities, engine speed fluctuation amplitudes and torque production, are strictly connected. The presented methodology is based on two main steps. The first step relies on the identification of the dynamic system model that allows to get torque harmonic from the corresponding engine speed components. The identification could be done by two methods, the first one requiring the knowledge of the value of the reciprocating masses with high precision, and the other one making use of different tests at the same speed but with different loads, in order to estimate separately both the reciprocating masses and the system model. The second step, which constitutes the main focus of this paper, relies on the identification of the relationship between the mean indicated torque and its harmonics. The study of this relationship has been carried out in particular in this paper for a multijet diesel engine and for a gasoline engine. Many tests were performed on different driveline configuration, both in a test-cell, and on-board. Once indicated torque and its harmonic components have been evaluated from in-cylinder pressure signals, identification of the relationship has been possible. Influence of the type of combustion performed has been discussed, as also the effects related to cylinder filling and injection timings.
Measurement of Biodiesel Blend and Conventional Diesel Spray Structure Using X-Ray Radiography
Authors: Kastengren A. L. , Powell C. F. , Im K.-S. , Wang Y.-J. , Wang J.
Published: June 2009

The near-nozzle structure of several non-evaporating biodiesel blend sprays has been studied using x-ray radiography. Radiography allows quantitative measurements of the fuel distribution in sprays to be made with high temporal and spatial resolution. Measurements have been made at different values of injection pressure, ambient density, and with two different nozzle geometries to understand the influences of these parameters on the spray structure of the biodiesel blend. These measurements have been compared to corresponding measurements of Viscor, a diesel calibration fluid, to demonstrate the fuel effects on the spray structure. Generally, the biodiesel blend spray has a similar structure to the spray of Viscor. For the nonhydroground nozzle used in this study, the biodiesel blend spray has a slightly slower penetration into the ambient gas than the Viscor spray. The cone angle of the biodiesel blend spray is generally smaller than that of the Viscor spray, indicating that the biodiesel blend spray is denser than the Viscor spray. For the hydroground nozzle, both fuels produce sprays with initially wide cone angles that transition to narrow sprays during the steady-state portion of the injection event. These variations in cone angle with time are timed later for the biodiesel blend spray than for the Viscor spray, indicating that the dynamics of the injector needle as it opens are somewhat different for the two fuels.
Modeling Soot Formation Using Reduced PAH Chemistry in n-Heptane Lifted Flames With Application to Low Temperature Combustion
Authors: Vishwanathan Gokul , Reitz Rolf D.
Published: June 2009

A numerical study of in-cylinder soot formation and oxidation processes in n-heptane lifted flames using various soot inception species has been conducted. In a recent study by the authors, it was found that the soot formation and growth regions in lifted flames were not adequately represented by using acetylene alone as the soot inception species. Comparisons with a conceptual model and available experimental data suggested that the location of soot formation regions could be better represented if polycyclic aromatic hydrocarbon (PAH) species were considered as alternatives to acetylene for soot formation processes. Since the local temperatures are much lower under low temperature combustion (LTC) conditions, it is believed that significant soot mass contribution can be attributed to PAH rather than to acetylene. To quantify and validate the above observations, a reduced n-heptane chemistry mechanism has been extended to include PAH species up to four fused aromatic rings (pyrene). The resulting chemistry mechanism was integrated into the multidimensional CFD code KIVA-CHEMKIN for modeling soot formation in lifted flames in a constant volume chamber. The investigation revealed that a simpler model that only considers up to phenanthrene (three fused rings) as the soot inception species has good possibilities for better soot location predictions. The present work highlights and illustrates the various research challenges toward accurate qualitative and quantitative predictions of soot for new low emission combustion strategies for I.C. engines.
3D CFD Simulations of Hydrogen Fuelled Spark Ignition Engine
Authors: Adgulkar Dinesh D. , Deshpande N. V. , Thombre S. B. , Chopde I. K.
Published: June 2009

By supporting hydrogen as an alternative fuel to the conventional fuel i.e. gasoline, new era of renewable and carbon neutral energy resources can be introduced. Hence, development of hydrogen fuelled internal combustion engine for improved power density and less emission of NOx has become today’s need and researchers are continuously extending their efforts in the improvement of hydrogen fuelled internal combustion engine. In this work, three dimensional CFD simulations were performed using CFD code (AVL FIRE) for premixed combustion of hydrogen. The simplified 3D geometry of engine with single valve i.e. inlet valve was considered for the simulation. Various combustion models for spark ignition for hydrogen i.e. Eddy Breakup model, Turbulent Flame Speed Closure Combustion Model, Coherent Flame model, Probability Density Function model were tested and validated with available simulation results. Results obtained in simulation indicate that the properties of hydrogen i.e. high flame speed, wide flammability limit, and high ignition temperature are among the main influencing factors for hydrogen combustion being different than that of gasoline. Different parameters i.e. spark advance angle (TDC to 40° before TDC in the step of 5°), rotational speed (1200 to 3000 rpm in the step of 300 rpm), equivalence ratio (0.5 to 1.2 in the step of 0.1), and compression ratio (8, 9 and 10) were used to simulate the combustion of hydrogen in spark ignition engine and to investigate their effects on the engine performance, which is in terms of pressure distribution, temperature distribution, species mass fraction, reaction progress variable and rate of heat release for complete cycle. The results of power output for hydrogen were also compared with that of gasoline. It has been observed that power output for hydrogen is almost 12–15% less than that of gasoline.
Comparison of Stratified and Homogeneous Combustion in a Direct-Injected Two-Stroke Engine for Snowmobile Applications
Authors: Johnson Justin , Den Braven Karen R.
Published: June 2009

Gasoline direct injection (GDI) two-stroke engine technology has been developed for use in snowmobile applications. Applying GDI to a two-stroke engine significantly reduces emissions of unburned hydrocarbons and improves fuel economy by reducing or eliminating the short circuiting of fuel that occurs in conventional carbureted two-stroke engines. The GDI design allows for two different modes of combustion, stratified and homogeneous. Stratified combustion is typically used during idle and light to moderate loads at low engine speeds while homogeneous combustion is used at moderate to high loads and medium to high engine speeds. This work presents the process and results of determining which mode of combustion provides better fuel economy during cruise point operation, and where the transition from stratified to homogeneous combustion should occur in snowmobile operation. Results show that homogeneous calibration is the superior mode of combustion for the cruise points of a snowmobile.
Extending the Lean Limit of Natural Gas Engines
Authors: Evans R. L.
Published: June 2009

Two different methods to improve the thermal efficiency and reduce the emissions from lean-burn natural gas fuelled engines have been developed, and are described in this paper. One method used a “squish-jet” combustion chamber designed specifically to enhance turbulence generation, while the second method provided a partially stratified-charge mixture near the spark plug in order to enhance the ignition of lean mixtures of natural gas and air. The squish-jet combustion chamber was found to reduce Bsfc by up to 4.8% in a Ricardo Hydra engine, while the NOx – efficiency tradeoff was greatly improved in a Cummins L-10 engine. The partially stratified-charge combustion system extended the lean limit of operation in the Ricardo Hydra by some 10%, resulting in a 64% reduction in NOx emissions at the lean limit of operation. Both techniques were also shown to be effective in increasing the stability of combustion, thereby reducing cyclic variations in cylinder pressure.
Definition of a LES Numerical Methodology for the Simulation of Engine Flows on Fixed Grid
Authors: Brusiani Federico , Pelloni Piero , Cazzoli Giulio
Published: June 2009

To improve the overall engine performance, it is necessary to clearly understand the main unsteady phenomena that occur inside an IC engine. Since experimental technique can provide only lump parameters, the CFD numerical approach has been identified as a valid alternative tool to perform detailed investigations on the fluid dynamics behaviours. The numerical analysis of engine flows is commonly performed by using RANS approach. Adopting a RANS methodology only the mean flow variable distributions could be obtained because the time average of the generic flow variable fluctuation is zero by definition. To perform an effective analysis about the unsteady characteristic of a generic flow and, in particular, of an engine flow it is necessary to improve the numerical solution level adopting the LES (Large Eddy Simulation) approach. LES solves directly the large scales of motion (responsible for the main energy transport inside the flow) while only the small scales are modelled using a Sub-Grid Scale model. Moreover, the LES approach could also be used as test bench case to properly define and understand how it is possible to improve the solution accuracy of RANS simulation. This paper regards the LES analysis of a steady non-reactive wall-bounded flow over a test bench engine geometry. In particular, two LES models, i.e., the Wall Adaptive Local Eddy-Viscosity (WALE) [25] model and the one-equation Dynamic Model by Kim and Menon [23, 24, 29] have been tested. The numerical set-up has been defined performing a preliminary parametric CFD simulations on a basic flow over a backward facing step case. In particular, a bounded second order central differencing scheme was adopted and a discussion of the kinetic energy conservation attitude of such a scheme is performed. LES results have been compared to available experimental LDA measurements of mean and rms fluctuations of both axial and tangential velocity components and with numerical predictions obtained by an optimized RANS simulation of the same case. This paper shows the advantages and the limits of the LES simulation approach applied to IC engine flows.
The Effects of Power Cylinder Design Parameters on Lube Oil Consumption of a Heavy Duty Diesel Engine
Authors: Akalin Ozgen , Cobanoglu Selcuk , Toygar Ahu , Gul Ozcan , Kurnaz Goktan , Ergen O. Rustu
Published: June 2009

In order to achieve fast and accurate oil consumption measurements, a real-time sulfur tracing method was developed employing a quadrupole mass spectrometer to analyze the sulfur dioxide concentration in the exhaust stream. A sampling system was designed to measure the oil consumption of separate cylinder groups sequentially under identical running conditions. The developed method enables the comparison of oil consumption of separate cylinder groups without disturbing the engine’s operation. Using this experimental method, steady-state oil consumption of a turbo-charged heavy-duty diesel engine was measured under various engine operating conditions. The effect of cylinder bore surface texture parameters on total lube oil consumption of the test engine was investigated simultaneously using a cylinder block having dissimilar honing patterns on each cylinder group. The results showed that the lube oil consumption of the engine is significantly affected by the cylinder bore surface roughness. The cylinder sets with high surface roughness demonstrated significantly higher lube oil consumption when the cylinder sets with high and low surface roughness was compared simultaneously.
Inline Pump Internal Flow Characterization for Optimized Diesel Injection
Authors: Chiatti G. , Chiavola O. , Palmieri F.
Published: June 2009

The injection process optimization plays a key role in diesel engine development activities, both for pollutant formation control and performance improvement. The present paper focuses on relatively small diesel units, equipped with fully mechanical injection systems; in detail, the considered system layout is based on the use of spring injectors; the amount of delivered fuel is controlled by the positioning of the pump plunger groove. The paper highlights the role of the inline pump and the influence of fuel characteristics on the system operation. By means of a three-dimensional numerical flow study, the behavior of pump fuel passages and delivery valve is simulated. Then, on the basis of the system features, a complete lumped/one-dimensional numerical model is realized, in which the discharge coefficients evaluated through the three-dimensional simulation are employed. Fuel injection rate and local pressure time histories are investigated, paying specific attention to the occurrence of the relevant phenomena in the system components. Obtained results are compared with experimental data.
Combined Experimental and Numerical Analysis of the Influence of Air-to-Fuel Ratio on Cyclic Variation of High Performance Engines
Authors: Forte Claudio , Bianchi Gian Marco , Corti Enrico , Fantoni Stefano
Published: June 2009

The Cycle by Cycle Variation (CCV) of a SI engine is analyzed by combining experimental tests and numerical investigations. The quantification of CCV is based on the evaluation of the Coefficient of Variance (COV) of IMEP. The analysis of the experimental pressure data shows an increase in CCV towards leaner mixture conditions. The evaluation of the Heat Release Rate from the in-cylinder pressure traces reveals the strong influence of the early stages of combustion on the variability of the flame evolution. In order to evaluate the influence on CCV of local air equivalence ratio cycle-to-cycle variability and mixture homogeneity in the chamber, a numerical CFD methodology for the simulation of the combustion process has been proposed. The results reproduce with reasonable accuracy the increase in CCV with leaner combustions and put the basis for a deeper insight into the complex phenomena involved in the combustion process by the use of parametric analysis.
Lumped Parameter Approach for DPF Management in Stationary Diesel Engines
Authors: Chiatti G. , Chiavola O. , Falcucci G.
Published: June 2009

During the last years, emission standards for diesel engines have got more and more severe not only for light- and heavy-duty road application, but also in the nonroad, locomotive and stationary fields. In this paper, the results of a Lumped Parameter (LP) model for Diesel Particulate Filter (DPF) management in stationary diesel engines are presented. The developed LP model allows to predict the pressure drop and soot layer growth in time along the trap channel. In the model, the equations are tuned by means of a complete CFD analysis of the gas flux through a wall-flow DPF. The difference in flow field due to the radial distance from the filter axis and its effects on the soot growth inside the channel are taken into account as the loading phase proceeds. The temperature evolution during the regeneration process of the device is predicted, too, thus permitting a complete management of the filter in control applications.
Analysis of the Air-Fuel Mixture Control in Natural Gas Fuelled Turbocharged Engines
Authors: Payri Francisco , Galindo Jose , Luja´n Jose Manuel , Climent He´ctor
Published: June 2009

The use of natural gas in medium and heavy duty engines for public transportation is a promising way for reducing exhaust emissions. Computer simulations, coupled with engine tests, have arisen as a valuable methodology to study the gas exchange processes inside intake and exhaust manifolds. A wave action model is set up in order to simulate a natural gas fuelled turbocharged engine. Once the modeling results show good agreement when comparing with measured data at different running conditions in terms of fluid dynamic properties, the model is used to study the air-fuel mixture process in the intake manifold and optimize the injection system behavior. Comparisons of modeled air-fuel composition in the cylinders are performed with both single and multi-point injection strategies. These cylinder to cylinder air-fuel mixture dispersion problems are analyzed at both steady and transient engine running conditions. Steady operation is performed correctly when using single-point injection since the gas mixer upstream the throttle valve enhances the mixing process. However, significant gas dispersion among cylinders appears during an engine load transient. With multi-point injection the critical parameter is the injection timing, since it is usually larger than the intake stroke period and, if it is not conveniently arranged, significant natural gas dispersion among cylinders may appear at both steady and transient running conditions.
Parametrical Study of Pump-to-Injector Line Pressure Over Various Input Parameters of Liquid Fuel Compression Engine
Authors: Chen Gong
Published: June 2009

The fuel injection and peak fuel injection pressures of a liquid fuel compression-ignition engine, such as a diesel engine or a diesel engine burning an alternative liquid fuel, are affected by fuel physical properties, and various engine design and operation input parameters. The fuel physical properties under this investigation include fuel density, fuel bulk modulus of elasticity, and fuel viscosity. The design and operation input parameters studied include the engine speed and the injector nozzle configuration parameters, such as the number of holes per injector nozzle, the dimensions of the hole, and the nozzle fuel flow discharge coefficient. The work of this paper analytically investigates the effects of those input parameters on pump-to-injector line fuel pressure and peak pressure. An understanding and simplified modeling of the fuel peak pressure affected by those property and input parameters are developed. The variations of the fuel pressure parameters over varying the fuel properties and the input parameters are analyzed and predicted. Results from this study indicate that, as the fuel bulk modulus of elasticity varies, the initial fuel pressure build-up period would be affected more significantly, with a less-significant variation in the fuel-line peak pressure. Among those fuel physical properties, the fuel density has a relatively significant effect on the fuel peak pressure. The effects of the various design and operation input parameters on the fuel peak pressure and related injection parameters are also studied and presented.