Computational Studies on Charge Stratification and Fuel-Air Mixing in a New Two-Stroke Engine

2005 ◽  
Author(s):  
Shamit Bakshi ◽  
T. N. C. Anand ◽  
R. V. Ravikrishna
Keyword(s):  
Initial Conditions ◽  
Computational Study ◽  
Three Dimensional ◽  
The State ◽  
Operating Conditions ◽  
Injection System ◽  
Critical Parameters ◽  
Mixing Process ◽  
Air Mixing ◽  
Stroke Engine

In this paper, detailed computational study is presented which helps to understand and improve the fuel-air mixing in a new direct-mixture-injection two-stroke engine. This new air-assisted injection system-based two-stroke engine is being developed at the Indian Institute of Science, Bangalore over the past few years. It shows the potential to meet emission norms such as EURO-II and EURO-III and also deliver satisfactory performance. This work proposes a comprehensive strategy to study the air-fuel mixing process in this engine and shows that this strategy can be potentially used to improve the engine performance. A three-dimensional compressible flow code with standard k–ε turbulence model with wall functions is developed and used for this modeling. To account for the moving boundary or piston in the engine cylinder domain, a non-stationary and deforming grid is used in this region with stationary cells in the ports and connecting ducts. A flux conservation scheme is used in the domain interface to allow the in-cylinder moving mesh to slide past the fixed port meshes. The initial conditions for flow parameters are taken from the output of a three-dimensional scavenging simulation. The state of the inlet charge is obtained from a separate modeling of the air-assisted injection system of this engine. The simulation results show that a large, near-stoichiometric region is present at most operating conditions in the cylinder head plane. The state of the in-cylinder charge at the onset of ignition is studied leading to a good understanding of the mixing process. In addition, sensitivity of two critical parameters on the mixing and stratification is investigated. The suggested parameters substantially enhance the flammable proportion at the onset of combustion. The predicted P–θ from a combustion simulation supports this recommendation.

Classical harmonic oscillator approach of a helical-wiggler free-electron laserwith axial guide field

2000 ◽  
Vol 78 (12) ◽  
pp. 1069-1085 ◽  
Author(s):  
M N Rhimi ◽  
R El-Bahi ◽  
A W Cheikhrouhou
Keyword(s):  
Fixed Point ◽  
Free Electron ◽  
Initial Conditions ◽  
Three Dimensional ◽  
Basic Feature ◽  
Operating Conditions ◽  
The Other ◽  
Guide Field ◽  
Constants Of Motion ◽  
Definition Of

Electron beam dynamics in a helical-wiggler free-electron laser (FEL) with a uniform axial guide magnetic field are studied using a three-dimensional Hamiltonian approach. The basic feature of the analysis is the definition of a rotational variable, [Formula: see text], that plays the primordial role in lowering to the half the dimension of the quadratic Hamiltonian as a system of two uncoupled oscillators with definite frequencies and amplitudes. It is through applying this variable in the vicinity of a fixed point that the Heisenberg picture of the dynamics of the particles comes to light, leading thus to the association of the steady-state ideal helical trajectories with arbitrary trajectories. The approach recognized the usual two constants of motion, one being the total energy while the other is the canonical axial angular momentum, Pz'. If the value of the latter is such that a fixed point exists, the Hamiltonian is expanded about the fixed point up to second order. The so-obtained oscillator characteristic frequencies allowed one to study the different modes of propagation and to identify, and then avoid the problematic operating conditions of the FEL concerned. On the other hand, the amplitudes of the oscillations, which do depend on the frequencies, are fortunately found to be constants of motion and then controlled by the boundary conditions (initial conditions). PACS Nos.: 52.40-w, 52.60+h, 42.55.Tb, 52.75Ms

Analysis on the Mixing Process in a Heavy-Duty Diesel Engine under Different Conditions of Spray Position

2013 ◽  
Vol 732-733 ◽  
pp. 387-391
Author(s):  
Ye Yuan ◽  
Guo Xiu Li ◽  
Yu Song Yu ◽  
Yang Jie Xu
Keyword(s):  
Combustion Chamber ◽  
Three Dimensional ◽  
Mixing Process ◽  
Heavy Duty ◽  
Power Performance ◽  
Position Change ◽  
Heavy Duty Diesel Engine ◽  
Air Mixing ◽  
Circumferential Distribution ◽  
Heavy Duty Diesel

In order to investigate the influence of spray position on fuel air mixing quality, three-dimensional numerical simulation of the working process of a heavy-duty diesel was conducted. To quantitatively study the mechanism of the effect of spray position on fuel air mixing process, the deviation of spray centroid was introduced to describe the spray position change in combustion chamber. The results show that the gas intake swirl can affect the spatial distribution of spray in combustion chamber under three directions in cylindrical coordinate, in which the circumferential distribution is affected most. It then can be concluded that the spray can be limited to the vicinity of the combustion chamber axis. Better spray position, which is more helpful for the process of fuel air mixing and combustion, can be achieved by using optimal swirl, so that the power performance will be improved.

On Pattern Selection in Three-Dimensional Bénard-Marangoni Flows

2012 ◽  
Vol 11 (3) ◽  
pp. 893-924 ◽  
Author(s):  
Arne Morten Kvarving ◽  
Tormod Bjøntegaard ◽  
Einar M. Rønquist
Keyword(s):  
Numerical Experiments ◽  
Initial Conditions ◽  
Computational Study ◽  
Fluid Layer ◽  
Three Dimensional ◽  
Fixed Number ◽  
Random Initial Condition ◽  
Initial Condition ◽  
Convection Pattern ◽  
Number Of Cells

AbstractIn this paper we study Bénard-Marangoni convection in confined containers where a thin fluid layer is heated from below. We consider containers with circular, square and hexagonal cross-sections. For Marangoni numbers close to the critical Marangoni number, the flow patterns are dominated by the appearance of the well-known hexagonal convection cells. The main purpose of this computational study is to explore the possible patterns the system may end up in for a given set of parameters. In a series of numerical experiments, the coupled fluid-thermal system is started with a zero initial condition for the velocity and a random initial condition for the temperature. For a given set of parameters we demonstrate that the system can end up in more than one state. For example, the final state of the system may be dominated by a steady convection pattern with a fixed number of cells, however, the same system may occasionally end up in a steady pattern involving a slightly different number of cells, or it may end up in a state where most of the cells are stationary, while one or more cells end up in an oscillatory state. For larger aspect ratio containers, we are also able to reproduce dislocations in the convection pattern, which have also been observed experimentally. It has been conjectured that such imperfections (e.g., a localized star-like pattern) are due to small irregularities in the experimental setup (e.g., the geometry of the container). However, we show, through controlled numerical experiments, that such phenomena may appear under otherwise ideal conditions. By repeating the numerical experiments for the same non-dimensional numbers, using a different random initial condition for the temperature in each case, we are able to get an indication of how rare such events are. Next, we study the effect of symmetrizing the initial conditions. Finally, we study the effect of selected geometry deformations on the resulting convection patterns.

Effect of Subgrid Modeling on the In-Cylinder Unsteady Mixing Process in a Direct Injection Engine

2003 ◽  
Vol 125 (2) ◽  
pp. 435-443 ◽  
Author(s):  
K. Sone ◽  
S. Menon
Keyword(s):  
Direct Injection ◽  
Three Dimensional ◽  
Mixing Process ◽  
Ic Engine ◽  
Eddy Simulation ◽  
Spatial Features ◽  
Air Mixing ◽  
Local Grid ◽  
Mixed Field ◽  
Direct Injection Spark Ignition

Fuel-air mixing in a direct injection spark ignition (DISI) engine occurs in a highly unsteady, turbulent and three-dimensional flow. As a result, any cycle-to-cycle unsteady variation in the mixing process can directly impact the performance of the DISI engine. To study the unsteady process in these engines, we have developed and implemented a large-eddy simulation (LES) approach with an innovative subgrid scalar mixing model based on the linear-eddy mixing (LEM) model into a commercial IC engine code (KIVA-3V). Time-averaged results of the simulations using the new LES version (KIVALES) are compared to the steady-state predictions of the original KIVA-3V. Significantly different in-cylinder turbulent fuel-air mixing is predicted by these two methods. Analysis shows that KIVALES resolves spatial features larger than the grid and that the subgrid kinetic energy adjusts to the LES resolution. As a result, KIVALES captures a highly unsteady, anisotropic fuel-air mixing process whereas a more diffused mixed field is predicted by the original KIVA-3V. This ability of KIVALES is attributed to the subgrid closure which scales the subgrid dissipation with the local grid size and thus, decreases the overall dissipation in the flow.

Coupled Aerothermodynamics Optimization for the Cooling System of a Turbine Vane

2013 ◽  
Vol 136 (5) ◽  
Author(s):  
Zhongran Chi ◽  
Jing Ren ◽  
Hongde Jiang
Keyword(s):  
Genetic Algorithm ◽  
Temperature Distribution ◽  
System Design ◽  
Cooling System ◽  
Three Dimensional ◽  
Critical Issue ◽  
Operating Conditions ◽  
Critical Parameters ◽  
Pin Fin ◽  
Optimization Search

The cooling system design for air-cooled turbines is a critical issue in modern gas turbine engineering. Advances in the computational fluid dynamics (CFD) technology and optimization methodology are providing new prospects for turbine cooling system design, in the sense that the optimum cooling system of the vanes and blades could be designed automatically by the optimization search coupled with the full three-dimensional conjugate heat transfer (CHT) analysis. An optimization platform for air-cooled turbines, which consists of the genetic algorithm (GA), a mesh generation tool (Coolmesh), and a CHT solver is presented in this paper. The optimization study was aimed at finding the optimum cooling structure for a 2nd stage vane with, simultaneously, an acceptable metal temperature distribution and limited amount of coolant. The vane was installed with an impingement and pin-fin cooling structure. The optimization search involved the design of the critical parameters of the cooling system, including the size of the impingement tube, diameter and distribution of impingement holes, and the size and distribution of the pin-fin near trailing edge. The design optimization was carried out under two engine operating conditions in order to explore the effects of different boundary conditions. A constant pressure drop was assumed within the cooling system during each optimization. To make the problem computationally faster, the simulations were approached for the interior only (solid and coolant). A weighted function of the temperature distribution and coolant mass flow was used as the objective of the single objective genetic algorithm (SOGA). The result showed that the optimal cooling system configuration with considerable cooling performance could be designed through the SOGA optimization without human interference.

Stability of Laminated Composites

1992 ◽  
Vol 45 (2) ◽  
pp. 81-101 ◽  
Author(s):  
A. N. Guz’ ◽  
Vik N. Chekhov
Keyword(s):  
Composite Materials ◽  
Three Dimensional ◽  
Laminated Composite ◽  
Operating Conditions ◽  
Critical Parameters ◽  
Characteristic Classes ◽  
Deformable Solid ◽  
Stability Problems ◽  
Laminated Composite Materials ◽  
Laminated Materials

The characteristic special feature of deformation behavior of modern laminated composite materials and structural elements fabricated from these materials, at current levels of loading and operating conditions is the occurrence of the purely three-dimensional stress-deformed state. In this process some specific mechanical phenomena and effects may occur, which is impossible to describe within the framework of applied or approximate approaches existing currently in deformable solid body mechanics. The structure of massive laminated materials may be included in this class of phenomena when the critical parameters of the problem depend only on the ratio between mechanical and geometrical characteristics of single layers and are independent of the dimensions and the form of the total laminated body as a whole. Since this phenomenon may be the beginning of the process of fracture of these materials, and the loss of the load-carrying capacity of structure elements fabricated from them, we consider below, in three-dimensional formulation, the problem of the surface and internal instability in laminated composite materials under compressive surface loads. The classification of the existing types of stability problems is presented for laminated materials and approaches for their solution presented in the literature. On the basis of three-dimensional linearized stability theory, within the framework of the piecewise-homogeneous media model, the general formulation of the most characteristic classes of stability problems of laminated materials is given in Lagrangian coordinates at small and finite, homogeneous and inhomogeneous precritical deformation. Analytic and variational methods of investigation of formulated problems are given with application to various models of laminated bodies models, in accordance with accepted stability criteria. The accuracy of these models is evaluated, based on the example of the solution of certain model problems; the range of application is given for existing applied and approximate approaches to the analysis of formulated problems. Results of solution of specific problems are given; specific mechanical effects, characteristic for the phenomenon considered, are found. Recommendations are formulated for engineering design and computational methods. New promising areas of research are pointed out for the problem of laminated composite materials stability.

The Effect of Subgrid Modeling on the In-Cylinder Unsteady Mixing Process in a Direct Injection Engine

2001 ◽  
Author(s):  
Kazuo Sone ◽  
Suresh Menon
Keyword(s):  
Large Scale ◽  
Direct Injection ◽  
Three Dimensional ◽  
Navier Stokes ◽  
Mixing Process ◽  
Simulation Code ◽  
Ic Engine ◽  
Engine Simulation ◽  
Air Mixing ◽  
Linear Eddy Model

Abstract The process of fuel-air mixing in the Direct Injection Spark Ignition (DISI) engine is highly unsteady and three-dimensional with wide cycle-to-cycle variations involving vaporization of droplets and its interaction with large-scale turbulent flow field. Although the majority of the past numerical studies of mixing in an Internal Combustion (IC) engines have employed Reynolds-Averaged Navier-Stokes (RANS) equations with empirical turbulence model, here we have implemented a Large-Eddy Simulations (LES) with the Linear-Eddy Model (LEM) for subgrid scalar mixing into a commercial IC engine simulation code (KIVA-3V). This study shows that when time-accurate effects are included significantly different results are obtained. These differences between the original KTVA-3V and the new KIVALES in predicting the in-cylinder turbulent fuel-air mixing are discussed. LES shows highly unsteady, anisotropic in-cylinder fuel-air mixing process compared to the original KIVA-3V. The implications for combustion is also discussed.

scholarly journals Flow and Heat Transfer in a Ribbed U-Duct Under Typical Engine Conditions

1998 ◽  
Author(s):  
T. I-P. Shih ◽  
Y.-L. Lin ◽  
M. A. Stephens ◽  
M. K. Chyu ◽  
K. C. Civinskas
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Gas Turbines ◽  
Computational Study ◽  
Three Dimensional ◽  
Eddy Diffusivity ◽  
Reynolds Stress Model ◽  
Operating Conditions ◽  
Coolant Flow ◽  
Flow And Heat Transfer

Computations were performed to study the three-dimensional flow and heat transfer in a ribbed U-shaped duct of square cross section under operating conditions that are typical of industrial gas turbines. Basically, all walls were maintained at a temperature of 800 K, and the coolant air at the duct inlet had a temperature of 550 K and a pressure of 10 atm. Both rotating and non-rotating cases were investigated. When rotating, the angular speed was 3,600 rpm. The Reynolds number based on the duct hydraulic diameter was set at 350,000, which represents an upper limit in coolant flow. The results obtained in this study were compared with those from previous numerical studies with a lower Reynolds number, namely 25,000, which represents a lower limit in coolant flow. This computational study is based on the ensemble-averaged conservation equations of mass, momentum (compressible Navier-Stokes), and energy. Turbulence is modelled by two low-Reynolds number k-ω models: an SST version with isotropic eddy diffusivity and a nonlinear version with anisotropic eddy diffusivity from an explicit algebraic Reynolds stress model. Solutions were generated by using a cell-centered finite-volume method, that is based on flux-difference splitting and a diagonalized alternating-direction implicit scheme with local time-stepping and V-cycle multigrid.

OPERATIONAL STATE OF BRIDGES OF UKRAINE

2019 ◽  
pp. 57-68
Author(s):  
Larysa Bodnar ◽  
Petro Koval ◽  
Sergii Stepanov ◽  
Liudmyla Panibratets
Keyword(s):  
Management System ◽  
The State ◽  
Operating Conditions ◽  
Bridge Management ◽  
Bridge Management System ◽  
Program Complex ◽  
Operating Condition ◽  
Software Complex ◽  
Automatic Mode ◽  
The Status

A significant part of Ukrainian bridges on public roads is operated for more than 30 years (94 %). At the same time, the traffic volume and the weight of vehicles has increased significantly. Insufficient level of bridges maintenance funding leads to the deterioration of their technical state. The ways to ensure reliable and safe operation of bridges are considered. The procedure for determining the predicted operational status of the elements and the bridge in general, which has a scientific novelty, is proposed. In the software complex, Analytical Expert Bridges Management System (AESUM), is a function that allows tracking the changes in the operational status of bridges both in Ukraine and in each region separately. The given algorithm of the procedure for determining the predicted state of the bridge using a degradation model is described using the Nassie-Schneidermann diagram. The model of the degradation of the bridge performance which is adopted in Ukraine as a normative one, and the algorithm for its adaptation to the AESUM program complex with the function to ensure the probabilistic predicted operating condition of the bridges in the automatic mode is presented. This makes it possible, even in case of unsatisfactory performance of surveys, to have the predicted lifetime of bridges at the required time. For each bridge element it is possible to determine the residual time of operation that will allow predict the state of the elements of the structure for a certain period of time in the future. Significant interest for specialists calls for the approaches to the development of orientated perspective plans for bridge inspection and monitoring of changes in the operational status of bridges for 2009-2018 in Ukraine. For the analysis of the state of the bridge economy, the information is available on the distribution of bridges by operating state related to the administrative significance of roads, by road categories and by materials of the structures. Determining the operating state of the bridge is an important condition for making the qualified decisions as regards its maintenance. The Analytical Expert Bridges Management System (AESUM) which is implemented in Ukraine, stores the data on the monitoring the status of bridges and performs the necessary procedures to maintain them in a reliable and safe operating condition. An important result of the work is the ability to determine the distribution of bridges on the public roads of Ukraine, according to operating conditions established in the program complex of AESUM, which is presented in accordance with the data of the current year. In conditions of limited funding and in case of unsatisfactory performance of surveys, it is possible to make the reasonable management decisions regarding the repair and the reconstruction of bridges. Keywords: bridge management system, operating condition, predicted operating condition, model of degradation, bridge survey plan, highway bridge.

Three-Dimensional Computational Study of Natural Convection in a Non-Uniformly Heated Vertical Open-Ended Channel

2014 ◽  
Author(s):  
Oxana A. Tkachenko ◽  
Svetlana A. Tkachenko ◽  
Victoria Timchenko ◽  
John A. Reizes ◽  
Guan Heng Yeoh ◽  
...  
Keyword(s):  
Natural Convection ◽  
Computational Study ◽  
Three Dimensional
Sign in / Sign up

Export Citation Format

Share Document