- Madison, Wisconsin, United States
Rolf Reitz
University of Wisconsin-Madison, Engine Research Center, Faculty Member
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A reduced chemical reaction mechanism is developed and validated in the present study for multi-dimensional diesel HCCI engine combustion simulations. The motivation for the development of the reduced mechanism is to enhance the... more
A reduced chemical reaction mechanism is developed and validated in the present study for multi-dimensional diesel HCCI engine combustion simulations. The motivation for the development of the reduced mechanism is to enhance the computational efficiency of engine ...
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In this study we identify components of a typical biodiesel fuel and estimate both their individual and mixed thermo-physical and transport properties. We then use the estimated mixture properties in computational simulations to gauge the... more
In this study we identify components of a typical biodiesel fuel and estimate both their individual and mixed thermo-physical and transport properties. We then use the estimated mixture properties in computational simulations to gauge the extent to which combustion is modified when ...
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The theoretical basis and numerical implementation of KIVA, a multidimensional computer code for the simulation of atomization and vaporization processes in the injection of a liquid through a round hole into a compressed gas, are... more
The theoretical basis and numerical implementation of KIVA, a multidimensional computer code for the simulation of atomization and vaporization processes in the injection of a liquid through a round hole into a compressed gas, are described. KIVA is based on the blob-injection model of Reitz and Diwakar (1987), taking into account the effects of liquid inertia, surface tension, and the aerodynamic forces on the jet, as well as drop collision and coalescence and the effect of drops on turbulence in the gas. The predictions of KIVA for different injection regimes are compared with published experimental data in extensive graphs, and good agreement is demonstrated.
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ABSTRACT A new spray/wall interaction model was developed with emphasis on the simulation of diesel-like spray impingement generated by high injection pressures, which is widely used in direct-injection gasoline and diesel engines. In... more
ABSTRACT A new spray/wall interaction model was developed with emphasis on the simulation of diesel-like spray impingement generated by high injection pressures, which is widely used in direct-injection gasoline and diesel engines. In contrast to traditional spray/wall interaction models, lift forces were considered on the wall spray droplets in the new model, which generates a vortex at the leading edge of the wall spray instead of droplet rebound or splash. In addition, a wall-jet submodel was adopted to correct the droplet-gas relative velocity in the calculation of drag and lift forces on the droplets. Grid dependency was also significantly reduced in the new model due to the implementation of the wall-jet submodel. The wall-jet submodel was extended to cover both normal and oblique impingements, which are relevant in engines with a side-mounted injector. In the new model a new correlation was also developed to estimate the splashed mass ratio for each individual impact droplet, which provides a more accurate prediction of the overall spray impingement process. Extensive validations of the new model were performed through comparisons against measurements from a variety of diesel spray impingement experiments, instead of just using single drop or drop train impingement experiments. The results indicate that the new model matches experimental measurements very well and can be used for the prediction of spray/wall interaction, especially under the conditions relevant to modern direct-injection diesel and gasoline engines.
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Computational and experimental studies on the effects of oxygenated fuels with single and split high-pressure fuel injections were conducted at both high and low load engine operating conditions. The oxygenates were a long chained ester... more
Computational and experimental studies on the effects of oxygenated fuels with single and split high-pressure fuel injections were conducted at both high and low load engine operating conditions. The oxygenates were a long chained ester and ether blended with conventional diesel fuel. An improved version of the KIVA-II multidimensional engine code was used in the study, and the soot model
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The effects of fuel-spray targeting on mixture development, combustion, and pollutant formation were investigated for a late-injection low-temperature combustion (LTC) operating condition in an optically accessible heavy-duty diesel... more
The effects of fuel-spray targeting on mixture development, combustion, and pollutant formation were investigated for a late-injection low-temperature combustion (LTC) operating condition in an optically accessible heavy-duty diesel engine. Equivalence-ratio maps, derived from toluene fuel-tracer fluorescence measurements, quantify the effects of fuel-jet targeting on mixture preparation processes under non-combusting conditions. Planar laser-induced fluorescence of formaldehyde (H2CO), hydroxyl radical (OH), and polycyclic aromatic hydrocarbons (PAH) provide complementary measurements during the combustion process from fuel-lean to fuel-rich reaction zones. Three different injector nozzles with included angles of 124°, 152° and 160° yield unique jet–wall and jet–jet interactions. The baseline 152° nozzle directs the fuel jet toward the vertical center of the piston bowl-wall, where the jets impinge on the wall and merge with neighboring jets prior to the peak heat-release rate. Fuel-rich jet–jet interaction regions develop between the jets near the floor of the bowl, which is where the majority of soot and/or PAH formation occurs. These fuel-rich jet–jet interactions can be reduced by either a more narrow injection angle (124°) or a wider angle injection (160°), both of which lead to decreased soot formation. However, jet–wall interactions may play an important role for late-cycle bulk flows. With the 160° injection, less bulk-fluid motion in the piston bowl occurs, leading to extensive quenched regions throughout the center of the combustion chamber. By contrast, the 124° injection enhances large-scale fluid motion, transporting hot second-stage ignition regions into the fuel-lean quenched mixtures at the center of the chamber, potentially improving late-cycle oxidation of unburned hydrocarbons (UHC) and carbon monoxide (CO).
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The structure of first- and second-stage combustion is investigated in a heavy-duty, single-cylinder optical engine using chemiluminescence imaging, Mie-scatter imaging of liquid-fuel, and OH planar laser-induced fluorescence (OH-PLIF)... more
The structure of first- and second-stage combustion is investigated in a heavy-duty, single-cylinder optical engine using chemiluminescence imaging, Mie-scatter imaging of liquid-fuel, and OH planar laser-induced fluorescence (OH-PLIF) along with calculations of fluorescence quenching. Three different diesel combustion modes are studied: conventional non-diluted high-temperature combustion (HTC) with either (1) short or (2) long ignition delay, and (3) highly diluted low-temperature combustion (LTC) with early fuel injection. For the short ignition delay HTC condition, the OH fluorescence images show that second-stage combustion occurs mainly on the fuel jet periphery in a thickness of about 1 mm. For the long ignition delay HTC condition, the second-stage combustion zone on the jet periphery is thicker (5–6 mm). For the early-injection LTC condition, the second-stage combustion is even thicker (20–25 mm) and occurs only in the down-stream regions of the jet. The relationship between OH concentration and OH-PLIF intensity over a range of equivalence ratios is estimated from quenching calculations using collider species concentrations predicted by chemical kinetics simulations of combustion. The calculations show that both OH concentration and OH-PLIF intensity peak near stoichiometric mixtures and fall by an order of magnitude or more for equivalence ratios less than 0.2–0.4 and greater than 1.4–1.6. Using the OH fluorescence quenching predictions together with OH-PLIF images, quantitative boundaries for mixing are established for the three engine combustion modes.
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A highly diluted, low-flame-temperature diesel engine combustion strategy with two separate fuel-injections per cycle was investigated using simultaneous optical diagnostics at a low-load operating condition. In-cylinder processes were... more
A highly diluted, low-flame-temperature diesel engine combustion strategy with two separate fuel-injections per cycle was investigated using simultaneous optical diagnostics at a low-load operating condition. In-cylinder processes were visualized with a suite of laser/imaging diagnostics. The cool flame first-stage ignition reactions occur along the entire length of the jet for the first combustion event. For both injections, the second-stage ignition
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A nine-step phenomenological soot model has been implemented into the KIVA-3V code for predicting soot formation and oxidation processes in diesel engines. The model involves nine generic steps, i.e., fuel pyrolysis, precursor species... more
A nine-step phenomenological soot model has been implemented into the KIVA-3V code for predicting soot formation and oxidation processes in diesel engines. The model involves nine generic steps, i.e., fuel pyrolysis, precursor species (including acetylene) formation and oxidation, soot particle inception, particle coagulation, surface growth and oxidation. The fuel pyrolysis process leads to acetylene formation and it is described by a single-step reaction. The particle inception occurs via a generic gas-phase precursor species, and the precursor is the product of an irreversible reaction from acetylene. The acetylene addition reaction contributes to soot surface growth. The particle coagulation affects both particle size and number density. The oxidation of soot particles includes two mechanisms—Nagle and Strickland-Constable's O2 oxidation mechanism and Neoh et al.'s OH oxidation mechanism. The quasi-steady state assumption is applied to an H2–O2–CO system for calculating OH concentration. Both acetylene and precursor species have their own consumption paths, each of which is described by a single-step oxidation reaction.Validations of the model have been conducted over a wide range of engine conditions from conventional to PCCI-like combustion. Two engine examples (a heavy-duty diesel engine and a light-duty diesel engine) are presented in this paper. The predictions are compared against measurements, and the applicability of the model to multi-dimensional diesel simulations is assessed. The model's capability of predicting the soot distribution structure in a conventional diesel flame is included in discussion as well. The work reveals that the nine-step model is not only computationally efficient but also fundamentally sound. The model can be applied to diesel engine combustion analysis and, after calibration, is suitable to be integrated with genetic algorithms for system optimization over a controllable range of operations.
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Diesel engine simulation results using two different combustion models are presented in this study, namely the representative interactive flamelet (RIF) model and the direct integration of computational fluid dynamics and CHEMKIN. Both... more
Diesel engine simulation results using two different combustion models are presented in this study, namely the representative interactive flamelet (RIF) model and the direct integration of computational fluid dynamics and CHEMKIN. Both models have been implemented into an improved version of the KIVA code. The KIVA/RIF model uses a single flamelet approach and also considers the effects of vaporization on
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It is well known that injection strategies including the injection timing and the injection rate-shape play an important role in determining engine performance, especially pollutant emissions. But how the injection timing and the... more
It is well known that injection strategies including the injection timing and the injection rate-shape play an important role in determining engine performance, especially pollutant emissions. But how the injection timing and the injection rate-shape quantitatively affect the performance of diesel low temperature combustion (LTC) is still not well understood. In this paper, the KIVA–CHEMKIN computational fluid dynamics (CFD) code with an improved spray model is used to simulate the spray and combustion processes of diesel LTC with early and late injection timings and seven different injection rate-shapes. The validation of the models is based on comparisons with laser diagnostic and in-cylinder pressure data under a low load operating condition. It is concluded that the use of early injection provides lower soot, HC and CO emissions but higher NOx emissions than the late injection. A rectangular-type (case1) and boot-type (case 4) injection rate-shape displays the potential to reduce the soot, HC and CO emissions compared the other generic rate-shapes considered.
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Current spray models based on the Lagrangian-droplet and Eulerian-fluid (LDEF) method in the KIVA-3V code are strongly mesh dependent due to errors in predicting the droplet–gas relative velocity and errors in describing droplet–droplet... more
Current spray models based on the Lagrangian-droplet and Eulerian-fluid (LDEF) method in the KIVA-3V code are strongly mesh dependent due to errors in predicting the droplet–gas relative velocity and errors in describing droplet–droplet collision and coalescence processes. To reduce the mesh dependence, gas-jet theory is introduced to predict the droplet–gas relative velocity, and a radius of influence (ROI) of collision methodology is established for each gas phase cell to estimate the collision probability for each parcel in the cell. Spray and combustion processes in a low temperature combustion diesel engine under early and late injection strategies with a fine mesh were predicted using the conventional LDEF model and compared with the measurements of soot, OH, fuel liquid and vapor distributions obtained by laser based diagnostics including, PLIF, LII, and Mie scattering. Then, the KIVA-3V code implemented with the improved spray model based on the gas-jet model and modifications of the spray models was utilized to simulate the processes on a relatively coarse numerical mesh. Comparison of the simulations between the fine and coarse meshes shows that the improved spray model can greatly reduce the mesh dependence for low temperature combustion diesel engine CFD simulations.
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ABSTRACT A new spray computational fluid dynamics (CFD) model that comprises gas-jet and radius-of-influence collision, mean collision time, and interpolation method improvements was used to reduce grid-size, hole-location, and time-step... more
ABSTRACT A new spray computational fluid dynamics (CFD) model that comprises gas-jet and radius-of-influence collision, mean collision time, and interpolation method improvements was used to reduce grid-size, hole-location, and time-step dependencies in modeling group-hole-nozzle sprays. The spray model was validated against experimental results obtained from spray visualization and phase Doppler particle analyzer systems. The spray characteristics including spray penetration and droplet sizes of group-hole nozzles were also studied. Standard CFD spray models show significant dependencies of grid size, hole location, and time step for the calculated spray penetration of group-hole nozzles. On the other hand, the new spray model reduced the dependencies successfully for the present nonevaporating spray cases. The calculated results agreed well with the experimental results in terms of both spray penetration and SMD distributions. It was found that the sprays of the group-hole nozzle exhibit similar spray penetrations to those of a single-hole nozzle with the same overall hole area. The computations indicate that the group-hole nozzle has advantages in the near field for reducing spray droplet sizes.
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... to be tightly coupled to the solution domain. This model [19]. ... On the other hand, global search methods, such as the genetic algorithm used in the present work, place teristics to solve the partial differential equations governing... more
... to be tightly coupled to the solution domain. This model [19]. ... On the other hand, global search methods, such as the genetic algorithm used in the present work, place teristics to solve the partial differential equations governing quasi-one-dimensional, unsteady, com-...
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ABSTRACT Various single and split injection schemes,are studied to provide a better understanding,of fuel distribution during cold starting in DI diesel engines. Improved spray-wall interaction, fuel film and multicomponent vaporization... more
ABSTRACT Various single and split injection schemes,are studied to provide a better understanding,of fuel distribution during cold starting in DI diesel engines. Improved spray-wall interaction, fuel film and multicomponent vaporization models,are used to analyze the combustion,processes. Better combustion,characteristics are obtained for the
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A computer model developed for describing multicomponent fuel vaporization, and ignition in diesel engines has been applied in this study to understand cold-starting and the parameters that are of significant influence on this phenomena.... more
A computer model developed for describing multicomponent fuel vaporization, and ignition in diesel engines has been applied in this study to understand cold-starting and the parameters that are of significant influence on this phenomena. This research utilizes recent improvements in spray vaporization and combustion models that have been implemented in the KIVA-II CFD code. Typical engine fuels are blends of various fuels species, i.e., multicomponent. Thus, the original single component fuel vaporization model in KIVA-II was replaced by a multicomponent fuel vaporization model (based on the model suggested by Jin and Borman). The model has been extended to model diesel sprays under typical diesel conditions, including the effect of fuel cetane number variation. Necessary modifications were carried out in the atomization and collision sub-models. The ignition model was also modified to account for fuel composition effects by modifying the Shell ignition model. The improved model was applied to simulate diesel engine cold-starting. The effect of fuel residual from previous cycles was studied and was found to be important. Other injection parameters, such as injection timing and duration were also studied. Another factor that was investigated was engine geometry and how it can be modified to improve on cold-starting in diesel engines. Cold-starting was found to be enhanced by the presence of a small fuel vapor residual and by a shorter injection duration, while engine geometry modifications were found to be helpful in selecting an optimum location on the cylinder head for an ignition aid. THE SIGNIFICANT NUh4BER of diesel engines which provide automotive power, together with recent concerns for the environment, resulted in the introduction of more legislation to limit their pollutant emissions. Of particular interest are the Nitrogen Oxides (NOx) and soot emissions. Both of these pollutants depend significantly on both the fuel and the injection system. The trend to lower emissions motivates new research efforts with the objective of improving engine performance. A significant fraction of engine emissions, particularly unburned hydrocarbons, is produced during the cold-starting phase of the engine operation. Furthermore, starting the diesel engine under cold ambient conditions represents a difficulty in itself Thus, more research is needed to identify mechanisms that would improve the cold-startability of the engine. Cold-starting is characterized as a situation where the engine does not fire at all for several cycles, or fires for one cycle and skips firing for the several following cycles, as
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The present paper introduces an approach for the automatic development of reduced reaction mechanisms for hydrocarbon combustion. An iterative reduction procedure is adopted with the aim of gradually reducing the number of species... more
The present paper introduces an approach for the automatic development of reduced reaction mechanisms for hydrocarbon combustion. An iterative reduction procedure is adopted with the aim of gradually reducing the number of species involved in the mechanism, while still maintaining its predictiveness in terms of not only ignition delay times, but also the time evolution of important species. In particular, a global error function is defined taking into account a set of 18 ignition delay calculations at different, engine-relevant, initial mixture compositions, temperatures and pressures. The choice of the species to be deleted is performed exploiting the element flux analysis method, first introduced by Revel et al.; when a global error function of the reduced mechanism exceeds the required accuracy, the collision frequencies and activation energies of selected reactions are corrected by means of a GA-based code. The procedure is repeated until the lowest number of species at the required global error tolerance is achieved. The methodology is applied to a detailed mechanism of ethanol combustion consisting of 58 species and 383 reactions to produce an optimal reduced mechanism of 33 species and 155 reactions.
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... engine application. Artificial neural networks (ANNs) purposes. Wickman et al. ... dgd2= CP1 0 g(t)dtD2 + CP1 0 g∞(t)dtD2 + P1 0 [g◊(t)]2 dt Without loss of generality, the input variables x i are ... Sample mean 219.8 4.91 0.91 A... more
... engine application. Artificial neural networks (ANNs) purposes. Wickman et al. ... dgd2= CP1 0 g(t)dtD2 + CP1 0 g∞(t)dtD2 + P1 0 [g◊(t)]2 dt Without loss of generality, the input variables x i are ... Sample mean 219.8 4.91 0.91 A simpler and more practical way is to fix certain Fig. ...
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With the exponentially increasing computational power of modern computers, multi-dimensional Computational Fluid Dynamics (CFD) has found more and more applications in diesel engine research, design and development since its initiation in... more
With the exponentially increasing computational power of modern computers, multi-dimensional Computational Fluid Dynamics (CFD) has found more and more applications in diesel engine research, design and development since its initiation in the late 1970s. Enhanced understandings of the physical processes of diesel combustion and correspondingly improved numerical models and methods have both driven simulations using multi-dimensional CFD tools from qualitative description towards quantitative prediction. To numerically resolve the complex physics of diesel combustion requires modelling of turbulent flows, high-pressure spray development, as well as combustion chemistry and relevant mechanism of pollutants formation. This chapter reviews the basic approach of multi-dimensional CFD modelling of diesel combustion, and focus is placed on the description of advanced turbulence, spray, and combustion models, and the introduction of popular CFD codes for engine simulations. In addition, recent efforts for reducing the computational expense of multi-dimensional CFD modelling are also discussed.
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High velocity, gas-assisted liquid drop atomization processes were investigated under well-controlled experimental conditions at elevated gas densities and room temperature. A monodisperse stream of drops which are generated by a... more
High velocity, gas-assisted liquid drop atomization processes were investigated under well-controlled experimental conditions at elevated gas densities and room temperature. A monodisperse stream of drops which are generated by a vibrating-orifice drop generator was injected into a transverse high velocity gas stream. The gas density and air jet velocity were adjusted independently to keep the Weber numbers constant. The Weber numbers studied were 72, 148, 270, and 532. The range of experimental conditions studied included the three drop breakup regimes previously referred to as bag, stretching/thinning and catastrophic breakup regimes. High-magnification photography was taken to study the microscopic breakup mechanisms in high velocity gas flow fields. When the Weber number is held constant at different gas densities and jet velocities, the results show that the microscopic breakup process is similar, even at high gas densities. At low Weber numbers, the photographs confirmed the existence of the bag breakup regime. The stretching/thinning breakup regime was observed for Weber numbers between 150 and 270. At Weber number = 532, the breakup in the catastrophic breakup regime occurred.
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Numerical simulations of direct injection (DI) heavy-duty diesel engine combustion over the entire engine operating range were conducted using the KIVA code, with modifications to the spray, combustion, turbulence, and heat transfer... more
Numerical simulations of direct injection (DI) heavy-duty diesel engine combustion over the entire engine operating range were conducted using the KIVA code, with modifications to the spray, combustion, turbulence, and heat transfer models. In this work, the effect of the rates of species conversion from reactants to products in the combustion model was investigated, and a characteristic-time combustion model was formulated to allow consideration of multiple characteristic time scales for the major chemical species. In addition, the effect of engine operating conditions on the model formulation was assessed, and correlations were introduced into the combustion model to account for the effects of residual gas and Exhaust Gas Recirculation (EGR). The predictions were compared with extensive engine test data. The calculation results had good overall agreement with the experimental cylinder pressure and heat release results, and the multiple-time-scale combustion model is shown to give improved emissions predictions compared to a previous single-time-scale model. Overall, the NOâ predictions are in good agreement with the experiments. The soot predictions are also in reasonable agreement with the measured particulates at medium and high loads. However, at light loads, the agreement deteriorates, possibly due to the neglect of the contribution of SOF in the soot model predictions.
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The engine industry is currently facing severe emissions mandates. Pollutant emissions from mobile sources are a major source of concern. For example, US EPA mandates require emissions of particulate and nitrogen oxides (NOx) from... more
The engine industry is currently facing severe emissions mandates. Pollutant emissions from mobile sources are a major source of concern. For example, US EPA mandates require emissions of particulate and nitrogen oxides (NOx) from heavy-duty diesel engine exhaust to drop at least 90 percent between 1998 and 2010. Effective analysis of the combustion process is required to guide the selection of technologies for future development since exhaust after-treatment solutions are not currently available that can meet the required emission reduction goals. The goal of this project is to develop methods to optimize and control Low Temperature Combustion Diesel technologies (LTC-D) that offers the potential of nearly eliminating engine NOx and particulate emissions at reduced cost over traditional methods by controlling pollutant emissions in-cylinder.; The work was divided into 5 Tasks, featuring experimental and modeling components:; 1.) Fundamental understanding of LTC-D and advanced model development,; 2.) Experimental investigation of LTC-D combustion control concepts,; 3.) Application of detailed models for optimization of LTC-D combustion and emissions,; 4.) Impact of heat transfer and spray impingement on LTC-D combustion, and; 5.) Transient engine control with mixed-mode combustion.; As described in the final report (December 2008), outcomes from the research included providing guidelines to the engine and energy industries for achieving optimal low temperature combustion operation through using advanced fuel injection strategies, and the potential to extend low temperature operation through manipulation of fuel characteristics. In addition, recommendations were made for improved combustion chamber geometries that are matched to injection sprays and that minimize wall fuel films. The role of fuel-air mixing, fuel characteristics, fuel spray/wall impingement and heat transfer on LTC-D engine control were revealed. Methods were proposed for transient engine operation during load and speed changes to extend LTC-D engine operating limits, power density and fuel economy. Low emissions engine design concepts were proposed and evaluated.
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A study was performed of the distortion and breakup mechanisms of liquid drops injected into a transverse high velocity air jet at room temperature and atmospheric pressure. The investigation included the use of ultra-high magnification,... more
A study was performed of the distortion and breakup mechanisms of liquid drops injected into a transverse high velocity air jet at room temperature and atmospheric pressure. The investigation included the use of ultra-high magnification, short-exposure photography to study the three drop breakup regimes previously referred to as the bag breakup regime, the shear or boundary-layer stripping breakup regime, and the ‘catastrophic’ breakup regime. In the experiments the initial diameters of the injected diesel fuel drops were 69, 121 and 198 μm, and the transverse air jet velocity was varied from 68 to 331 m/s. The experimental conditions correspond to drop initial Weber numbers of 56, 260 and 463 for the three breakup regimes. The drop Reynolds numbers (based on gas properties) ranged from 509 to 2488. It was found that the drop breakup process occurs in two stages. During the first stage, under the action of aerodynamic pressure, the drop distorts from its undisturbed spherical shape and becomes flattened, or disk shaped, normal to the air flow direction. This feature exists in all three drop breakup regimes. A dynamic drag model that is a modified version of the DDB (Dynamic Drag and Breakup) model and accounts for the increase of both the drop's frontal area and its drag coefficient as a function of its distortion was used to analyze the drop trajectory and its distortion during the first stage of the drop breakup process. During the second stage of the drop breakup process, the three drop breakup regimes display different breakup features. In the bag breakup regime the appearance and growth of holes on the bag sheet blown out of the center of the flattened drop is the dominant reason for the breakup; in the so-called shear or boundary-layer stripping breakup regime the results indicate that bending of the flattened drop's edge under the action of aerodynamic pressure, followed by production of folds on the bent sheet results in production of ligaments aligned in the direction of the air flow; and in the ‘catastrophic’ breakup regime the growth of capillary waves on the flattened drop surfaces, combined with the bending and folding of the sheet edge makes the breakup process demonstrate ‘catastrophic’ breakup characteristics. In addition, the experimental results confirm that for drops with different sizes, the same breakup regimes appear when the Weber number is held constant, and the Reynolds number does not play a dominant role. These results thus cast considerable doubt on the validity of the widely used ‘shear’ or ‘boundary-layer stripping’ drop breakup theories in which viscous effects would be important.
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Two different geometries of the intake valves on the cylinder head of a four-valve large-bore diesel engine were compared in terms of their swirl generation mechanisms in the cylinder during the intake process. The swirl generation level... more
Two different geometries of the intake valves on the cylinder head of a four-valve large-bore diesel engine were compared in terms of their swirl generation mechanisms in the cylinder during the intake process. The swirl generation level and flow resistance were measured using a swirl meter on a steady flow rig and the detailed intake flow structure was studied using LDV measurements of the in-cylinder bulk flow velocity and turbulence intensity. The effects of changes in the maximum valve lift were also studied for each type of valve arrangement. Methods for calculating the swirl moment from the LDV data are presented and discussed by comparing with the swirl meter results. It was found that the aligned valve port arrangement (valves located at equal distances from the symmetry axis) generates higher swirl due to its eccentricity with respect to the intake port. In an inclined valve port engine (valves at different distances from the symmetry axis), increasing the maximum valve lift was found to improve the swirl generation capability significantly, even though it generated less swirl overall due to swirl cancellation at low valve lifts.
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... Gokul Vishwanathan a & Rolf D. Reitz a * pages 1050-1082. ... Ladommatos , N. , Song , H. , and Zhao , H. 2002 . Measurements and predictions of diesel soot oxidation rates . Proc. Inst. Mech. Eng. Pt. D: J. Automobile... more
... Gokul Vishwanathan a & Rolf D. Reitz a * pages 1050-1082. ... Ladommatos , N. , Song , H. , and Zhao , H. 2002 . Measurements and predictions of diesel soot oxidation rates . Proc. Inst. Mech. Eng. Pt. D: J. Automobile Eng. , 216 , 677 . [Web of Science ®] View all references). ...
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The effects of thermal and mixing conditions of the in-cylinder charge in internal combustion (IC) engines on emissions in low-temperature combustion (LTC) regimes are analyzed numerically. In the analysis, concepts of an equilibrium... more
The effects of thermal and mixing conditions of the in-cylinder charge in internal combustion (IC) engines on emissions in low-temperature combustion (LTC) regimes are analyzed numerically. In the analysis, concepts of an equilibrium temperature (Teq), peak temperature (Tpeak), and anticipated emissions (AE) are introduced. Also, mixture condition representations in temperature (T) vs. temperature (T) space (called T − T plot) and anticipated emissions (AE) vs. temperature (T) space (called AE − T plot) are proposed to represent the in-cylinder mixture quality and emission characteristics of the combustion. Five combustion pathways are identified using a Tpeak − Teq plot, and it is applied to describe both HCCI and DI engine combustion. An optimal temperature window and an optimal mixing window are defined and demonstrated in LTC engine operation. The results show that stratification of mixture temperature due to evaporation cooling and wall heat transfer significantly affects UHC/CO emissions of LTC engine operation. The T − T and AE − T plots reveal information about mixture inhomogeneity, completeness of burning of local mixtures, anticipated levels of emissions, and optimal timing of mixing that can maximize improvements in emissions. The new method of analysis is useful to identify and understand the evolution of in-cylinder mixture conditions in engine combustion.
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A multi-dimensional code has been developed to study the effects of injection pressure and nozzle hole inlet conditions on diesel engine performance and emissions. The code includes a new liquid core and spray breakup model. The models... more
A multi-dimensional code has been developed to study the effects of injection pressure and nozzle hole inlet conditions on diesel engine performance and emissions. The code includes a new liquid core and spray breakup model. The models were validated using spray visualization images obtained from a single-cylinder version of the Caterpillar 3406 heavy-duty truck engine instrumented with an endoscope system. The computational results were also compared with experimental emissions data. The results show that combustion and emissions predictions are controlled by the details of the spray model. With modifications to the spray model to account for Rayleigh-Taylor and Kelvin-Helmholtz drop breakup mechanisms, the predicted liquid and vapor-fuel penetration agrees well with that measured. The models were applied over a wide range of engine operating conditions and were found to provide good prediction accuracy. The simulations also showed that sharp edged-inlet nozzles give significantly lower particulate emissions than rounded-inlet nozzles with the same rate-of-injection profile as has been seen experimentally.
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... The EGR technique (the mixing of a part of the combustion gases with the unburned mixture) has been used successfully in diesel engines to reduce the NO x emissions due to its thermal diluent effect, resulting in a lower peak cylinder... more
... The EGR technique (the mixing of a part of the combustion gases with the unburned mixture) has been used successfully in diesel engines to reduce the NO x emissions due to its thermal diluent effect, resulting in a lower peak cylinder temperature and thus in a corresponding ...
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A vaporization model for multi-component fuel sprays is described. The discrete multi-component (DMC) fuel approach was used to model the properties and composition of gasoline and diesel model fuels. Unsteady vaporization of single and... more
A vaporization model for multi-component fuel sprays is described. The discrete multi-component (DMC) fuel approach was used to model the properties and composition of gasoline and diesel model fuels. Unsteady vaporization of single and multi-component fuel droplets and sprays was considered for both normal and flash-boiling evaporation conditions. An unsteady internal heat flux model and a model for the determination of the droplet surface temperature were formulated. An approximate solution to the quasi-steady energy equation was used to derive an explicit expression for the heat flux from the surrounding gas to the droplet–gas interface, with inter-diffusion of fuel vapor and the surrounding gas taken into account. The density change of the drop as a function of temperature was also considered. In order to treat phase change under trans-critical conditions, a characteristic length was defined to determine the amount of vaporized fuel as a function of time. The present vaporization models were implemented into a multi-dimensional CFD code and applied to calculate evaporation processes of single and multi-component fuel droplets and sprays for various ambient temperatures and droplet temperatures. Differences between representing model fuels using the single and multi-component fuel descriptions are discussed.
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There is a need to reduce the computational expense of practical multidimensional combustion simulations. Simulation of Homogeneous Charge Compression Ignition (HCCI) engine processes requires consideration of detailed chemistry in order... more
There is a need to reduce the computational expense of practical multidimensional combustion simulations. Simulation of Homogeneous Charge Compression Ignition (HCCI) engine processes requires consideration of detailed chemistry in order to capture the ignition and combustion characteristics. Even with relatively coarse numerical meshes and reduced chemistry mechanisms, calculation times are still unacceptably long. For the simulation of Direct Injection (DI)
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Research Interests:
A three-dimensional computer code (KIVA) is being modified to include state-of-the-art submodels for diesel engine flow and combustion: spray atomization, drop breakup/coalescence, multi-component fuel vaporization, spray/well... more
A three-dimensional computer code (KIVA) is being modified to include state-of-the-art submodels for diesel engine flow and combustion: spray atomization, drop breakup/coalescence, multi-component fuel vaporization, spray/well interaction, ignition and combustion, wall heat transfer, unburned HC and NOx formation, soot and radiation and the intake flow process. Improved and/or new submodels which have been completed are: wall heat transfer with unsteadiness and compressibility, laminar-turbulent characteristic time combustion with unburned HC and Zeldo'vich NOx, and spray/wall impingement with rebounding and sliding drops. Results to date show that adding the effects of unsteadiness and compressibility improves the accuracy of heat transfer predictions; spray drop rebound can occur from walls at low impingement velocities (e.g., in cold-starting); larger spray drops are formed at the nozzle due to the influence of vaporization on the atomization process; a laminar-and-turbulent characteristic time combustion model has the flexibility to match measured engine combustion data over a wide range of operating conditions; and, finally the characteristic time combustion model can also be extended to allow predictions of ignition. The accuracy of the predictions is being assessed by comparisons with available measurements. Additional supporting experiments are also described briefly. To data, comparisons have been made with measured engine cylinder pressure and heat flux data for homogeneous charge, spark-ignited and compression-ignited engines, and also limited comparisons for diesel engines. The model results are in good agreement with the experiments.