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Technical Paper

Heavy-Duty Diesel Combustion Optimization Using Multi-Objective Genetic Algorithm and Multi-Dimensional Modeling

2009-04-20
2009-01-0716
A multi-objective genetic algorithm methodology was applied to a heavy-duty diesel engine at three different operating conditions of interest. Separate optimizations were performed over various fuel injection nozzle parameters, piston bowl geometries and swirl ratios (SR). Different beginning of injection (BOI) timings were considered in all optimizations. The objective of the optimizations was to find the best possible fuel economy, NOx, and soot emissions tradeoffs. The input parameter ranges were determined using design of experiment methodology. A non-dominated sorting genetic algorithm II (NSGA II) was used for the optimization. For the optimization of piston bowl geometry, an automated grid generator was used for efficient mesh generation with variable geometry parameters. The KIVA3V release 2 code with improved ERC sub-models was used. The characteristic time combustion (CTC) model was employed to improve computational efficiency.
Technical Paper

Experimental Assessment of Reynolds-Averaged Dissipation Modeling in Engine Flows

2007-09-16
2007-24-0046
The influence of the constant C3, which multiplies the mean flow divergence term in the model equation for the turbulent kinetic energy dissipation, is examined in a motored diesel engine for three different swirl ratios and three different spatial locations. Predicted temporal histories of turbulence energy and its dissipation are compared with experimentally-derived estimates. A “best-fit” value of C3 = 1.75, with an approximate uncertainty of ±0.3 is found to minimize the error between the model predictions and the experiments. Using this best-fit value, model length scale behavior corresponds well with that of measured velocity-correlation integral scales during compression. During expansion, the model scale grows too rapidly. Restriction of the model assessment to the expansion stroke suggests that C3 = 0.9 is more appropriate during this period.
Technical Paper

Particle Image Velocimetry Measurements in the Piston Bowl of a DI Diesel Engine

1994-03-01
940283
Particle Image Velocimetry (PIV) was used to make gas velocity and turbulence measurements in a motored diesel engine. The experiments were conducted using a single-cylinder version of the Caterpillar 3406 production engine. One of the exhaust valves and the fuel injector port were used to provide optical access to the combustion chamber so that modifications to the engine geometry were minimal, and the results are representative of the actual engine. Measurements of gas velocity were made in a plane in the piston bowl using TiO2 seed particles. The light sheet necessary for PIV was formed by passing the beam from a Nd:YAG laser through the injector port and reflecting the beam off a conical mirror at the center of the piston. PIV data was difficult to obtain due to significant out-of-plane velocities. However, data was acquired at 25° and 15° before top dead center of compression at 750 rev/min.
Technical Paper

Engine Development Using Multi-dimensional CFD and Computer Optimization

2010-04-12
2010-01-0360
The present work proposes a methodology for diesel engine development using multi-dimensional CFD and computer optimization. A multi-objective genetic algorithm coupled with the KIVA3V Release 2 code was used to optimize a high speed direct injection (HSDI) diesel engine for passenger car applications. The simulations were conducted using high-throughput computing with the CONDOR system. An automated grid generator was used for efficient mesh generation with 11 variable piston bowl geometry parameters. The first step in the procedure was to search for an optimal nozzle and piston bowl design. In this case, spray targeting, swirl ratio, and piston bowl shape were optimized separately for two full-load cases using simpler efficient combustion models (the characteristic time scale model and the shell ignition model). The optimal designs from the two optimizations were then validated using a combustion model with detailed chemistry (KIVA-CHEMKIN model and ERC n-heptane mechanism).
Technical Paper

On the Dependence of Spray Angle and Other Spray Parameters on Nozzle Design and Operating Conditions

1979-02-01
790494
In the Atomization regime, liquid jets breakup either within the nozzle or immediately upon entering the chamber gas and drops much smaller than the jet diameter are formed. The mechanism of Atomization, which is presently unknown, was investigated by the simultaneous use of two photographic techniques. The initial transient was observed with a 106 frames/s camera and the steady state by a technique similar to spark photography. The experiment range was: liquid pressure 500 to 2500 psia; five mixtures of water and glycerol to vary the liquid viscosity; air, nitrogen, helium, and xenon at up to 600 psia as chamber gases to separate gas pressure from gas density effects; and 14 nozzle designs. Not changed were the temperature (room value), the nozzle diameter (340 μ), and the surface tension (70 dyne/cm).
Technical Paper

The Influence of Swirl Ratio on Turbulent Flow Structure in a Motored HSDI Diesel Engine - A Combined Experimental and Numerical Study

2004-03-08
2004-01-1678
Simultaneous two-component measurements of gas velocity and multi-dimensional numerical simulation are employed to characterize the evolution of the in-cylinder turbulent flow structure in a re-entrant bowl-in-piston engine under motored operation. The evolution of the mean flow field, turbulence energy, turbulent length scales, and the various terms contributing to the production of the turbulence energy are correlated and compared, with the objectives of clarifying the physical mechanisms and flow structures that dominate the turbulence production and of identifying the source of discrepancies between the measured and simulated turbulence fields. Additionally, the applicability of the linear turbulent stress modeling hypothesis employed in the k-ε model is assessed using the experimental mean flow gradients, turbulence energy, and length scales.
Technical Paper

Effects of Piston Crevice Flows and Lubricant Oil Vaporization on Diesel Engine Deposits

2006-04-03
2006-01-1149
The effect of piston ring pack crevice flow and lubricant oil vaporization on heavy-duty diesel engine deposits is investigated numerically using a multidimensional CFD code, KIVA3V, coupled with Chemkin II, and computational grids that resolve part of the crevice region appropriately. Improvements have been made to the code to be able to deal with the complex geometry of the ring pack, and sub-models for the crevice flow dynamics, lubricating oil vaporization and combustion, soot formation and deposition were also added to the code. Eight parametric cases were simulated under reacting conditions using detailed chemical kinetics to determine the effects of variations of lube-oil film thickness, distribution of the oil film thickness, number of injection pulses, and the main injection timing on engine soot deposition. The results show that crevice-borne hydrocarbon species play an important role in deposit formation on crevice surfaces.
Technical Paper

Computations of a Two-Stroke Engine Cylinder and Port Scavenging Flows

1991-02-01
910672
A modification of the computational fluid dynamics code KIVA-II is presented that allows computations to be made in complex engine geometries. An example application is given in which three versions of KIVA-II are run simultaneously. Each version considers a separate block of the computational domain, and the blocks exchange boundary condition information with each other at their common interfaces. The use of separate blocks permits the connectedness of the overall computational domain to change with time. The scavenging flow in the cylinder, transfer pipes (ports), and exhaust pipe of a ported two-stroke engine with a moving piston was modeled in this way. Results are presented for three engine designs that differ only in the angle of their boost ports. The calculated flow fields and the resulting fuel distributions are shown to be markedly different with the different geometries.
Technical Paper

Application of Schlieren Optical Techniques for the Measurement of Gas Temperature and Turbulent Diffusivity in a Diesel Engine

1993-03-01
930869
A new technique which is based on optoacoustic phenomena has been developed for measuring in-cylinder gas temperature and turbulent diffusivity. In the experiments, a high energy Nd:YAG pulsed laser beam was focused to cause local ionization of air at a point in the combustion chamber. This initiates a shock wave and creates a hot spot. The local temperature and turbulent diffusivity are determined by monitoring the shock propagation and the hot spot growth, respectively, with a schlieren photography system. In order to assess the validity and accuracy of the measurements, the technique was also applied to a turbulent jet. The temperature measurements were found to be accurate to within 3%. Results from the turbulent jet measurements also showed that the growth rate of the hot spot diameter can be used to estimate the turbulent diffusivity. In-cylinder gas temperature measurements were made in a motored single cylinder Caterpillar diesel engine, modified for optical access.
Technical Paper

Two-Color Combustion Visualization of Single and Split Injections in a Single-Cylinder Heavy-Duty D.I. Diesel Engine Using an Endoscope-Based Imaging System

1999-03-01
1999-01-1112
An experimental study of luminous combustion in a modern diesel engine was performed to investigate the effect of injection parameters on NOX and soot formation via flame temperature and soot KL factor measurements. The two-color technique was applied to 2-D soot luminosity images and area-averaged soot radiation signals to obtain spatially and temporally resolved flame temperature and soot KL factor. The imaging system used for this study was based on a wide-angle endoscope that was mounted in the cylinder head and allowed different views of the combustion chamber. The experiments were carried out on a single-cylinder 2.4 liter D.I. diesel engine equipped with an electronically controlled common-rail injection system. Operating conditions were 1600 rpm and 75% load. The two-color results confirm that retarding the injection timing causes lower flame temperatures and NOX emissions but increased soot formation, independent of injection strategy.
Technical Paper

Multidimensional Modeling of the Effects of Radiation and Soot Deposition in Heavy-duty Diesel Engines

2003-03-03
2003-01-0560
A radiation model based on the Discrete Ordinates Method (DOM) was incorporated into the KIVA3v multidimensional code to study the effects of soot and radiation on diesel engine performance at high load. A thermophoretic soot deposition model was implemented to predict soot concentrations in the near-wall region, which was found to affect radiative heat flux levels. Realistic, non-uniform combustion chamber wall surface temperature distributions were predicted using a finite-element-based heat conduction model for the engine metal components that was coupled with KIVA3v in an iterative scheme. The more accurate combustion chamber wall temperatures enhanced the accuracy of both the radiation and soot deposition models as well as the convective heat transfer model. For a basline case, (1500 rev/min, 100% load) it was found that radiation can account for as much as 30% of the total wall heat loss and that soot deposition in each cycle is less than 3% of the total in-cylinder soot.
Technical Paper

An Experimental Assessment of Turbulence Production, Reynolds Stress and Length Scale (Dissipation) Modeling in a Swirl-Supported DI Diesel Engine

2003-03-03
2003-01-1072
Simultaneous measurements of the radial and the tangential components of velocity are obtained in a high-speed, direct-injection diesel engine typical of automotive applications. Results are presented for engine operation with fuel injection, but without combustion, for three different swirl ratios and four injection pressures. With the mean and fluctuating velocities, the r-θ plane shear stress and the mean flow gradients are obtained. Longitudinal and transverse length scales are also estimated via Taylor's hypothesis. The flow is shown to be sufficiently homogeneous and stationary to obtain meaningful length scale estimates. Concurrently, the flow and injection processes are simulated with KIVA-3V employing a RNG k-ε turbulence model. The measured turbulent kinetic energy k, r-θ plane mean strain rates ( 〈Srθ〉, 〈Srr〉, and 〈Sθθ〉 ), deviatoric turbulent stresses , and the r-θ plane turbulence production terms are compared directly to the simulated results.
Technical Paper

Modeling the Effects of Geometry Generated Turbulence on HCCI Engine Combustion

2003-03-03
2003-01-1088
The present study uses a numerical model to investigate the effects of flow turbulence on premixed iso-octane HCCI engine combustion. Different levels of in-cylinder turbulence are generated by using different piston geometries, namely a disc-shape versus a square-shape bowl. The numerical model is based on the KIVA code which is modified to use CHEMKIN as the chemistry solver. A detailed reaction mechanism is used to simulate the fuel chemistry. It is found that turbulence has significant effects on HCCI combustion. In the current engine setup, the main effect of turbulence is to affect the wall heat transfer, and hence to change the mixture temperature which, in turn, influences the ignition timing and combustion duration. The model also predicts that the combustion duration in the square bowl case is longer than that in the disc piston case which agrees with the measurements.
Technical Paper

Principal Component Analysis and Study of Port-Induced Swirl Structures in a Light-Duty Optical Diesel Engine

2015-04-14
2015-01-1696
In this work computational and experimental approaches are combined to characterize in-cylinder flow structures and local flow field properties during operation of the Sandia 1.9L light-duty optical Diesel engine. A full computational model of the single-cylinder research engine was used that considers the complete intake and exhaust runners and plenums, as well as the adjustable throttling devices used in the experiments to obtain different swirl ratios. The in-cylinder flow predictions were validated against an extensive set of planar PIV measurements at different vertical locations in the combustion chamber for different swirl ratio configurations. Principal Component Analysis was used to characterize precession, tilting and eccentricity, and regional averages of the in-cylinder turbulence properties in the squish region and the piston bowl.
Technical Paper

Intake Flow Simulation and Comparison with PTV Measurements

1999-03-01
1999-01-0176
Intake flow simulations were carried out for a prototype DISI engine using the standard k-ε model and the RNG k-ε model. The results were compared with PTV (transient water analog) measurements. The study was focused on low load operations with engine speed at 400 rev/min. Two cases were studied, a single intake case in which one intake port was blocked and a dual intake port case. In the computations, the results show that the standard k-ε model tends to produce higher turbulence levels when turbulence is generated and decays faster when turbulence dissipates. Different turbulence models predict almost the same flow structures. However, the effects of the turbulence model on the predicted tumble and swirl ratios are significant. The TKE distributions at BDC predicted by the two models are also different. The standard k-ε model seems to be more diffusive. Good agreements with PTV data were obtained in the single valve case with the RNG k-ε model.
Technical Paper

Pressure-Swirl Atomization in the Near Field

1999-03-01
1999-01-0496
To model sprays from pressure-swirl atomizers, the connection between the injector and the downstream spray must be considered. A new model for pressure-swirl atomizers is presented which assumes little knowledge of the internal details of the injector, but instead uses available observations of external spray characteristics. First, a correlation for the exit velocity at the injector exit is used to define the liquid film thickness. Next, the film must be modeled as it becomes a thin, liquid sheet and breaks up, forming ligaments and droplets. A linearized instability analysis of the breakup of a viscous, liquid sheet is used as part of the spray boundary condition. The spray angle is estimated from spray photographs and patternator data. A mass averaged spray angle is calculated from the patternator data and used in some of the calculations.
Technical Paper

Effects of Initial Conditions in Multidimensional Combustion Simulations of HSDI Diesel Engines

1999-03-01
1999-01-1180
The effects of numerical methodology in defining the initial conditions and simulating the compression stroke in D.I. diesel engine CFD computations are studied. Lumped and pointwise approaches were adopted in assigning the initial conditions at IVC. The lumped approach was coupled with a two-dimensional calculation of the compression stroke. The pointwise methodology was based on the results of an unsteady calculation of the intake stroke performed by using the STAR-CD code in the realistic engine and port geometry. Full engine and 60 deg. sector meshes were used in the compression stroke calculations in order to check the accuracy of the commonly applied axi-symmetric fluid dynamics assumption. Analysis of the evolution of the main fluid dynamics parameters revealed that local conditions at the time of injection strongly depend on the numerical procedure adopted.
Technical Paper

Studying the Roles of Kinetics and Turbulence in the Simulation of Diesel Combustion by Means of an Extended Characteristic-Time-Model

1999-03-01
1999-01-1177
A study was performed that takes into account both turbulence and chemical kinetic effects in the numerical simulation of diesel engine combustion in order to better understand the importance of their respective roles at changing operating conditions. An approach was developed which combines the simplicity and low computational and storage requests of the laminar-and-turbulent characteristic-time model with a detailed combustion chemistry model based on well-known simplified mechanisms. Assuming appropriate simplifications such as steady state or equilibrium for most of the radicals and intermediate species, the kinetics of hydrocarbons can be described by means of three overall steps. This approach was integrated in the KIVA-II code. The concept was validated and applied to a single-cylinder, heavy-duty engine. The simulation covers a wide range of operating conditions.
Technical Paper

Scaling Aspects of the Characteristic Time Combustion Model in the Simulation of Diesel Engines

1999-03-01
1999-01-1175
Combustion simulations utilizing the characteristic time combustion model have been performed for four DI diesel engines ranging in size from heavy-duty to large-bore designs. It has been found that the pre-factor to the turbulent characteristic time acts as a scaling parameter between the engines. This phenomenon is explained in terms of the non-equilibrium behavior of the turbulent time and length scales, as is encountered in the rapidly distorting, spray-induced flows of DI diesel engines. In fact, the equilibrium assumption between turbulence production and dissipation, which forms the basis for the employed k-ε-type turbulence models, does not hold in these situations. For such flows, the real turbulent dissipation time scale is locally proportional to the turbulent characteristic time scale which is determined by a typical eddy turnover time.
Technical Paper

Modeling the Use of Air-Injection for Emissions Reduction in a Direct-Injected Diesel Engine

1995-10-01
952359
This study investigates the effect of air-injection during the late combustion period produced by an air-cell on emissions from a direct injected diesel engine. The engine considered is a Caterpillar 3401 test engine which was modeled with an air-cell included as part of the piston geometry. A version of the KIVA-II code with updated submodels for diesel combustion and emissions was modified to allow for geometries with walls interior to the domain. This modified version of KIVA-II was then used to model an air-cell equipped diesel engine for four different air-cell configurations. Of the four air-cell configurations simulated, one proved successful in reducing the predicted engine emissions by more than a factor of two while simultaneously reducing NOx by a slight amount, thus moving the engine off its particulate-NOx tradeoff curve defined by varying the fuel injection timing.
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