En las últimas décadas ha avanzado mucho la comprensión científica sobre el proceso de combustión de los chorros diesel de inyección directa gracias al desarrollo de todo tipo de técnicas e instalaciones ópticas. Además, se han desarrollado y mejorado una gran cantidad de modelos de Dinámica de Fluidos Computacional (CFD), los cuales se usan para el desarrollo de motores altamente eficientes y con bajas emisiones. Sin embargo, debido a la complejidad de los procesos físicos y químicos involucrados en este proceso de combustión, así como a las limitaciones significativas de los experimentos, aún hay muchas cuestiones sin responder: ¿Cómo afecta la combustión a la dinámica del chorro? ¿Cómo cuantificar de forma efectiva la cantidad de hollín y la temperatura del mismo en la llama? ¿Cómo afecta el flujo del aire y las inyecciones partidas al desarrollo del chorro y a la formación de hollín en condiciones no quiescente? Para ayudar a resolver las preguntas planteadas, el objetivo de este trabajo se pone en investigar al dinámica del chorro y la formación de hollín de los chorros Diesel de inyección directa en condiciones quiescentes y no quiescentes por medio de diferentes técnicas ópticas. El trabajo se ha dividido en dos bloques principales. El primero está centrado en el estudio de las modificaciones inducidas por la combustión en la dinámica del chorro, así como la caracterización de la formación de hollín en la llama, todo ello en condiciones quiescentes. Dichas condiciones son proporcionadas por una maqueta de flujo continuo a alta presión y temperatura. La expansión radial y axial del chorro reactivo se ha investigado usando n-dodecano, n-heptano y una mezcla binaria de combustibles primarios de referencia (80% n-heptano y 20% iso-octano en masa), basándose en una base de datos existente medida mediante visualización de schlieren. Se ha estudiado tanto el papel de las condiciones de operación como las propiedades del combustible. A continuación se ha desarrollado por primera vez una técnica combinada de extinción-radiación, aplicada a la medida de hollín en llamas diesel. Gracias a esta técnica, tanto la fracción volumétrica de hollín como la temperatura se obtuvieron simultáneamente considerando los efectos de la autoabsorción en la radiación. Todo este trabajo se ha desarrollado dentro del marco de actividades de la Engine Combustion Network (ECN). El segundo bloque corresponde a la caracterización de la dinámica del chorro y de la formación de hollín en condiciones no quiescentes, que ocurren en la cámara de combustión de un motor monocilíndrico de dos tiempos con accesos ópticos. En esta parte, se ha llevado a cabo en primer lugar la visualización del chorro para una inyección única en condiciones no-reactivas y reactivas. Se han aplicado la visualización simultánea de schlieren y de la quimioluminiscencia del radical OH* para obtener la penetración del chorro y la longitud de despegue de la llama, mientras que la visualización de la extinción de ombroscopía difusa (DBI) se ha aplicado para cuantificar la formaciónde hollín. Los resultados se han comparado con los de la base de datos de la Engine Combustion Network antes mencionados, para estudiar los efectos del movimiento del aire inducido por el movimiento del pistón sobre el desarrollo del chorro y del hollín. Finalmente, se han usado diferentes estrategias de inyección partida para estudiar cómo la primera inyección afecta a los procesos de mezcla y a formación de hollín de la segunda, al cambiar el tiempo de separación entre ambos eventos de inyección o la cantidad inyectada en el primer pulso. / In recent decades, the scientific understanding of the combustion process of direct injection diesel spray has progressed a lot, thanks to the development of all kinds of optical facilities and techniques. In addition, a large amount of efficient and accurate Computational Fluid Dynamics (CFD) models, which are used for the design of highly efficient, low emission engines has been developed and improved. However, because of the complexity of the physical and chemical process involved in this combustion process, as well as significant experimental limitations and uncertainties, there are still a lot of remaining questions: How does combustion affect spray dynamics? How can in-flame soot amount and soot temperature be quantified effectively? How do the airflow and split-injection affect spray development and soot formation under non-quiescent conditions? To help solve these raised questions, the objective of this work is set to investigate the spray dynamics and soot formation process of direct injection diesel sprays under both quiescent and non-quiescent conditions by means of different optical techniques. The work has been divided into two main blocks. The first one is focused on the study of combustion-induced modifications in spray dynamics, as well as the characterization of in-flame soot formation under quiescent conditions. The quiescent conditions are provided by a kind of high-temperature high-pressure constant flow vessel. The radial and axial reacting spray expansion were investigated using n-dodecane, n-heptane and one binary blend of Primary Reference Fuels (80% n-heptane and 20% iso-octane in mass) based on an existing database from Schlieren imaging technique. Both operating conditions and fuel properties on this combustion-induced expansion were studied. Next, a combined extinction-radiation technique was first developed and applied in diesel spray soot measurement. Thanks to this technique, both the in-flame soot volume fraction and temperature were obtained simultaneously by considering the self-absorption effect on radiation. All this work has been carried out within the framework of activities of the engine combustion network (ECN). The second block corresponds to the characterization of spray dynamics and soot formation under non-quiescent conditions, which occur within the combustion chamber of a single-cylinder two-stroke optical engine. In this part, the spray visualization for single-injection under both non-reacting and reacting operating conditions was conducted first. Schlieren and OH * chemiluminescence were simultaneously applied to obtain the spray tip penetration and flame lift-off length, while the Diffuse Back Illumination (DBI) extinction imaging was applied to quantify the instantaneous soot formation. Results were compared with Engine Combustion Network database mentioned above to study the airflow effects induced by piston movement on spray and soot development. Finally, different split-injection strategies were used to study how the first injection affects the mixing and soot formation processes of the second one, by changing the dwell time between both injection events or the first injection quantity. / En les últimes dècades ha avançat molt la comprensió científica sobre el procés de combustió dels dolls dièsel d'injecció directa gràcies al desenvolupament de tot tipus de tècniques i instal·lacions òptiques. A més, s'han desenvolupat i millorat una gran quantitat de models de Dinàmica de Fluids Computacional (CFD), els quals s'usen per al desenvolupament de motors altament eficients i amb baixes emissions. No obstant açò, a causa de la complexitat dels processos físics i químics involucrats en aquest procés de combustió, així com de les limitacions significatives dels experiments, encara hi ha moltes qüestions sense respondre: Com afecta la combustió a la dinàmica del doll? Com quantificar de forma efectiva la quantitat de sutge i la temperatura del mateix en la flama? Com afecta el flux de l'aire i les injeccions partides al desenvolupament del doll i a la formació de sutge en condicions no quiescents? Per a ajudar a resoldre les preguntes plantejades, l'objectiu d'aquest treball es posa a investigar al dinàmica del doll i la formació de sutge dels dolls Dièsel d'injecció directa en condicions quiescents i no quiescents per mitjançant diferents tècniques òptiques. El treball s'ha dividit en dos blocs principals. El primer està centrat en l'estudi de les modificacions induïdes per la combustió en la dinàmica del doll, així com la caracterització de la formació de sutge en la flama, tot açò en condicions quiescents. Aquestes condicions són proporcionades per una maqueta de flux continu a alta pressió i temperatura. L'expansió radial i axial del doll reactiu s'ha investigat usant n-dodecà, n-heptà i una mescla binària de combustibles primaris de referència (80% n-heptà i 20% iso-octà en massa), basant-se en una base de dades existent mesura mitjançant visualització de schlieren. S'ha estudiat tant el paper de les condicions d'operació com les propietats del combustible. A continuació s'ha desenvolupat per primera vegada una tècnica combinada d'extinció-radiació, aplicada a la mesura de sutge en flames dièsel. Gràcies a aquesta tècnica, tant la fracció volumètrica de sutge com la temperatura es van obtenir simultàniament considerant els efectes de l'autoabsorció en la radiació. Tot aquest treball s'ha desenvolupat dins del marc d'activitats de la Engine Combustion Network (ECN). El segon bloc correspon a la caracterització de la dinàmica del doll i de la formació de sutge en condicions no quiescents, que ocorren en la cambra de combustió d'un motor monocilíndric de dos temps amb accessos òptics. En aquesta part, s'ha dut a terme en primer lloc la visualització del doll per a una injecció única en condicions no-reactives i reactives. S'han aplicat la visualització simultània de schlieren i de la quimioluminescència del radical OH* per a obtenir la penetració del doll i la longitud d'enlairament de la flama, mentre que la visualització de l'extinció d'ombroscopia difusa (DBI) s'ha aplicat per a quantificar la formaciónde sutge. Els resultats s'han comparat amb els de la base de dades de la Engine Combustion Network abans esmentats, per a estudiar els efectes del moviment de l'aire induït pel moviment del pistó sobre el desenvolupament del doll i del sutge. Finalment, s'han usat diferents estratègies d'injecció partida per a estudiar com la primera injecció afecta als processos de mescla i a formació de sutge de la segona, en canviar el temps de separació entre tots dos esdeveniments d'injecció o la quantitat injectada en el primer pols. / Xuan, T. (2017). Optical investigations on Diesel spray dynamics and in-flame soot formation [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/94626 / TESIS

Soot is a carbon particulate formed as a result of the combustion of fossil fuels. Due to the health hazard posed by the carbon particulate, government agencies have applied strict regulations to control soot emissions from road vehicles, airplanes, and industrial plants. Thus, understanding soot formation and evolution is critical. Practical combustion devices operate at high pressure and in the turbulent regime. Elevated pressures and turbulence on soot formation significantly and fundamental understanding of these complex interactions is still poor. In this study, the effects of pressure and turbulence on soot formation and growth are investigated numerically. As the first step, the evolution of the particle size distribution function (PSDF) and soot particles morphology are investigated in turbulent non-premixed flames. A Direct Simulation Monte Carlo (DSMC) code is developed and used. The stochastic reactor describes the evolution of soot in fluid parcels following Lagrangian trajectories in a turbulent flow field. The trajectories are sampled from a Direct Numerical Simulation (DNS) of an n-heptane turbulent non-premixed flame. Although individual trajectories display strong bimodality as in laminar flames, the ensemble-average PSDF possesses only one mode and a broad tail, which implies significant polydispersity induced by turbulence. Secondly, the effect of the flow and mixing fields on soot formation at atmospheric and elevated pressures is investigated in coflow laminar diffusion flames. The experimental observation and the numerical prediction of the spatial distribution are in good agreement. Based on the common scaling methodology of the flames (keeping the Reynolds number constant), the scalar dissipation rate decreases as pressure increases, promoting the formation of PAH species and soot. The decrease of the scalar dissipation rate significantly contributes to soot formation occurring closer to the nozzle and outward on the flames wings as pressure increases. The scaling of the scalar dissipation rate is not straightforward due to buoyancy effects. Finally, a new scaling approach of the flame at different pressures is introduced. In this approach, both Reynolds number and Grashof number are kept constant so that the effect of gravity is the same at all pressures. In order to keep Gr constant, this requires the diameter of the nozzle to be changed as pressures vary. This approach guarantees a similar non-dimensional flow field at all pressures and rules out the effect of hydrodynamics and mixing, so that only the effect of chemical kinetics on soot formation can be studied.

Soot formation from complex solid fuels, such as coal or biomass, is an under-studied and little understood phenomena which has profound physical effects. Any time a solid fuel is combusted, from coal-burning power plants to wildland fires, soot formation within the flame can have a significant influence on combustion characteristics such as temperature, heat flux, and chemical profiles. If emitted from the flame, soot particles have long-last effects on human health and the environment. The work in this dissertation focuses on creating and implementing computational models to be used for predicting soot mechanisms in a combustion environment. Three models are discussed in this work; the first is a previously developed model designed to predict soot yield in coal systems. This model was implemented into a computational fluid dynamic software and results are presented. The second model is a detailed-physics based model developed here. Validation for this model is presented along with some results of its implementation into the same software. The third model is a simplified version of the detailed model and is presented with some comparison case studies implemented on a variety of platforms and scenarios. While the main focus of this work is the presentation of the three computational models and their implementations, a considerable bulk of this work will discuss some of the technical tools used to accomplish this work. Some of these tools include an introduction to Bayesian statistics used in parameter inference and the method of moments with methods to resolve the 'closure' problem.

Emissions of soot and polycyclic aromatic hydrocarbons (PAHs) from incomplete burning of hydrocarbon fuels pose a great threat to the environment and human health. To reduce such emissions, a comprehensive understanding of their evolution process is essential. In this work, a series of research studies were conducted to evaluate sooting tendencies and to experimentally and theoretically develop PAH mechanisms. The sooting tendencies of oxygenated fuels were quantitively investigated in counterflow diffusion flames. Sooting limits are described by critical fuel and oxygen mole fractions, measured with a laser scattering technique. The addition of dimethyl ether displays non-monotonic behavior on sooting tendencies at elevated pressures, which is attributed to the chemical effect from kinetic simulations. The tendency of incipient soot formation of other oxygenated fuels (e.g., alcohol, acid, ether, ketone, and carbonate ester) was also assessed, using a similar approach. As the precursor of soot, PAH measurement using laser induced fluoresecnce was implemented to track the evolution processes from PAHs to incipient soot. Developing a PAH mechanism is essential to the understanding of soot formation; however, PAH formation and its growth process are not well understood. Based on previous research, PAHs with 5-membered rings are abundant in flames. Therefore, the growth of PAHs with 5-membered rings was investigated, using acenaphthylene (A2R5) as the example. The density functional theory (DFT) and the transition state theory (TST) were adopted to calculate potential energy surfaces and reaction rate coefficients. The existence of 5-membered rings appreciably impacts PAH production by facilitating the formation of planar PAHs with C2H substitution, thereby improving existing PAH mechanisms. In PAH mechanisms, the thermochemistry properties are not all calculated, but are hypothesized to be equal to those of a similar structure. The simulation accuracy of the hypothesis is explored here by discussing the sensitivity of the thermochemistry parameters in flame simulations. The group additivity method utilizing THERM codes is used to calculate thermochemistry properties. PAH loading affects the sensitivity of thermochemistry properties to both flame temperature and product yields. These results show that either accurate thermochemistry properties, or reverse reaction rates should be provided in the mechanism to improve simulation accuracy.

Soot formation is one of the most complex phenomena in combustion science and an understanding of the underlying physico-chemical mechanisms is important. This work adopted both experimental and numerical approaches to study soot formation in laminar counterfl ow diffusion flames. As polycyclic aromatic hydrocarbons (PAHs) are the precursors of soot particles, a detailed gas-phase chemical mechanism describing PAH growth upto coronene for fuels with 1 to 4 carbon atoms was validated against laminar premixed and counter- flow diffusion fl ames. Built upon this gas-phase mechanism, a soot model was then developed to describe soot inception and surface growth. This soot model was sub- sequently used to study fuel mixing effect on soot formation in counterfl ow diffusion flames. Simulation results showed that compared to the baseline case of the ethylene flame, the doping of 5% (by volume) propane or ethane in ethylene tends to increase the soot volume fraction and number density while keeping the average soot size almost unchanged. These results are in agreement with experimental observations. Laser light extinction/scattering as well as laser induced fluorescence techniques were used to study the effect of strain rate on soot and PAH formation in counterfl ow diffusion ames. The results showed that as strain rate increased both soot volume fraction and PAH concentrations decreased. The concentrations of larger PAH were more sensitive to strain rate compared to smaller ones. The effect of CO2 addition on soot formation was also studied using similar experimental techniques. Soot loading was reduced with CO2 dilution. Subsequent numerical modeling studies were able to reproduce the experimental trend. In addition, the chemical effect of CO2 addition was analyzed using numerical data. Critical conditions for the onset of soot were systematically studied in counterfl ow diffusion ames for various gaseous hydrocarbon fuels and at different strain rates. A sooting temperature index (STI) and a sooting sensitivity index (SSI) were proposed to present the sooting tendencies of different fuels and their sensitivities to strain rates.

No description available.

Numerous investigations have been conducted to determine the effect of fuel composition and molecular structure on particulate emissions using exhaust gas analysis, but relatively few measurements have been obtained in-cylinder or under conditions where fuel effects can be isolated from other variables. In this work, dimethoxymethane was used as the base fuel to produce a non-sooting flame in a constant volume combustion vessel at 1000 K, and a density of 16.6 kg/m3. A second fuel was then added incrementally to determine an incipient soot limit. Line-of-sight extinction measurements were used as the primary diagnostic tool to determine if a correlation exists between soot and fuel properties. These data indicate that fuels with carbon double bonds are more prone to soot than the single bonded fuels. Each of the four pure additives tested began to soot at a structure-weighted available oxygen-to-carbon ratio near one. The commonly used two-color method for measuring temperature and soot concentration (KL) was used as a secondary method. A method for calibrating and analyzing the uncertainty of the temperature and KL measurements with a single color RGB digital camera was demonstrated. Images of reacting jets of different soot concentrations are shown along with an uncertainty analysis. The resulting temperature and KL maps show uneven distributions for flames of various fuels. Analysis shows that the temperature and KL values of heavily sooting fuels are primarily a result of conditions (temperature and soot concentration) within a 1—2 mm region on the surface of the jet, where a turbulent diffusion flame is present. As soot concentration decreases, the region of influence affecting the result thickens, allowing more influence from within the jet, lowering the measured temperature. Therefore, a low-sooting jet appears to have a lower temperature than a high-sooting jet. Extinction and two-color soot measurement results were compared. The two-color KL values were seen to level off at around 0.5, but continue to increase monotonically as soot increased. The broad band method is therefore not good for absolute soot measurements. Natural luminosity measurements were sensitive to the first appearance of soot, but were non-linear.

The present work was conducted with the intent of developing a high-fidelity numerical model of a unique combustion flow problem combining multi-phase fuel injection with substantial momentum and temperature into a highly complex turbulent flow. This important problem is very different from typical and more widely known liquid fuel combustion problems and is found in practice in pulverized coal combustors and ducted rocket ramjets. As the ducted rocket engine cycle is only now finding widespread use, it has received little research attention and was selected as a representative problem for this research. Prior to this work, a method was lacking domestically and internationally to effectively model the ducted rocket engine cycle with confidence. In the ducted rocket a solid fuel gas generator is used to deliver a fuel-rich multi-phase mixture to the combustion chamber. When a valve is used to vary the fuel generator pressure, and thereby the delivered fuel flowrate, the engine is known as a Variable Flow Ducted Rocket (VFDR). The Aerojet MARC-R282 ramjet engine represents the worlds first VFDR flown, and the first in operational use. Although performance requirements were met, improvements are sought in the understanding of the ramjet combustion process with a future aim of reducing the visible exhaust and correcting uneven combustor heating patterns. For this reason the MARC-R282 combustor was selected as the baseline geometry for the present research, serving to provide a documented baseline case for numerical modeling and also being a good candidate to benefit from an improved understanding of the combustion process. In order to proceed with the present research, experiments were first carried out to characterize the gas generator particulate exhaust in terms of composition and particle size. Equilibrium thermochemistry was used to supplement these data to develop a gas phase combustion model. The gas phase reactions and resulting particle definition were modeling using the FLUENT Computational Fluid Dynamics (CFD) code for the baseline GQM-163A Supersonic Sea Skimming Missile (SSST) operating conditions. These results were compared to direct-connect ramjet ground tests in order to validate the analysis tool. Data were developed to understand the gas and solid phase fuel exhaust characteristics at the propellant surface, exiting the gas generator injector, and following secondary combustion with air. Particles were collected and analyzed from the fuel generator exhaust. While exhibiting some variation with time in the firing, they were roughly an average of 20 microns in diameter, in line with prior experience with pulverized coal combustion experiments. A computational model was developed based on coal combustion parameters using FLUENT. However, despite considerable effort, the CFD analysis was not able to predict effective burning of the carbon particles to the degree seen in testing. In addition, using equilibrium thermochemistry as a basis for determining the carbon particle content in the fuel exhaust, the CFD analysis resulted in trends in performance opposite to the test results. These facts led to a hypothesis that there was actually a significant fraction of small particles or much less carbon produced than equilibrium thermochemistry would predict. A parametric analysis was performed replacing the 20 micron soot particles with fine fraction particles, representing a fraction of the predicted equilibrium carbon soot being still in the gas phase as higher molecular weight hydrocarbons, or in the form of sub-micron particles. When almost all particles were replaced with fine fraction particles, the model was able to correctly predict absolute values of combustion efficiency as well as trends for different injector geometries. The presence of particles was apparent from the visible exhaust and collection data, however they were found not to play a significant role in the combustion process for this fuel and engine configuration. The robustness of the computational model was also evaluated by examining the effects of turbulence model, order of discretization, and grid size. Comparable trends and results were seen for all cases examined. With the successful development of this modeling tool and an improved understanding of the combustion process, future work is enabled to develop improved combustor flow management and fuel injection schemes to improve existing designs and develop new configurations. This research has served to advance the field of combustion modeling by providing: 1) a solid ducted rocket combustion modeling tool considering solid and gas phase combustion, 2) a correlation between primary combustion theory and particulate exhaust sampling, 3) low length/diameter ratio ducted rocket combustor modeling, and 4) combustor CFD coupled with solid particle tracking and combustion models. / Ph. D.

L’objectif principal de ce travail de recherche est d’améliorer les connaissances concernant l’influence de la morphologie de particules issues de combustion sur leur comportement thermophorétique. A cet effet, un dispositif tri-therme (3T) original permettant le dépôt par thermophorèse de ce type de particules a été développé. Cet instrument est composé de trois tubes concentriques, permettant la création d’un espace annulaire où un gaz chargé en particules est injecté. Le tube interne est refroidi et le tube externe est chauffé, créant ainsi un gradient de température dans l’espace annulaire. Les particules se déposent donc par effet thermophorétique sur la paroi froide du tube interne du dispositif. Ce dernier est basé sur la méthode dite de pénétration, où des mesures de concentrations à l’amont et à l’aval du dispositif permettent l’évaluation de l’efficacité de dépôt par effet thermophorétique. Un modèle du rendement de dépôt développé dans cette étude a permis par la suite de calculer le coefficient de diffusion thermophorétique Kth. Afin de valider la mise en œuvre de ce dispositif expérimental, nous avons évalué les coefficients Kth de billes de latex monodispersées et de deux types de brouillards d’huiles mono et polydispersés. Le bon accord trouvé entre ces valeurs du coefficient Kth et celles déterminées par le modèle de Beresnev et Chernyak ou par des études expérimentales antérieure, a permis la validation du dispositif 3T. Nous avons par la suite appliqué le dispositif avec des agrégats de suies de morphologie et de nature physico chimique variables. Les résultats obtenus mettent en évidence l’augmentation du coefficient de diffusion thermophorétique avec le nombre de particules primaires, et donc avec la taille de l’agrégat, confirmant ainsi les résultats obtenus par Mackowski et Brugière. Une confrontation entre les coefficients de diffusion thermophorétique Kth obtenus pour les différents types d’agrégats a été proposée. Cette confrontation a permis de dégager des tendances vis-à-vis de l’influence de la taille des particules primaires, de la dimension fractale Df et du ratio EC/TC sur le comportement thermophorétique des agrégats de suies / The main objective of this study is to improve the knowledge about the morphological influence of fractal aggregates on their thermophoretic behavior. For this purpose, an original tri thermal device aimed to capture this kind of particles by thermophoresis deposition was developed. This device is composed of three concentric tubes where particles flows through an annular space between the inner and outer tubes with imposed temperatures, the inner one is cooled and the outer is heated. Particles will deposit by thermophoresis on the cold wall of the inner tube. This device is based on the so called penetration method, where the deposition rate on a cold wall is obtained by particles concentrations measurements upstream and downstream of the test section. A deposition model developed in this study allowed us to determine the thermophoretic diffusion coefficient Kth. We validated the tri thermal device using monodispersed spherical latex particles and also mono and polydispersed spherical oil particles distributions. Indeed, a good agreement was found between our experimental determination of the thermophoretic diffusion coefficient and the theoretical values of Beresnev and Chernyak and also experimental results of the litterature. We finally conducted a study where we applied the device with soot aggregates that have variable morphology and physicochemical nature. This study confirmed the results presented by Mackowski and Brugière about the increase of the aggregates thermophoretic diffusion coefficients Kth with the primary particle number and therefore with the electrical mobility diameter. A confrontation between the coefficients Kth of the different types of aggregates allowed us to find an influence of the primary particles diameter, the fractal dimension Df and also the ratio EC/TC on the thermophoretic behavior of soot aggregates

A diesel fuel injector has been modified to allow rotationaround its axis, driven by an electric motor. Injections at upto 6000 rpm from the rotating injector have been investigatedunder the influence of air swirl on one optical research engineand one optically accessible heavy-duty diesel engine. The experiments show that changing from a normal, staticinjection to a sweeping injection has profound effects on sprayformation, dispersion and penetration. This influences thefuel/air-mixing, autoignition, combustion rate and emissionsformation. The spray propagation is stronger influenced byinjector rotation than by air swirl. The air entrainment into the spray increases forcounter-swirl rotation of the injector and this speeds up thevaporization and decreases the formation of soot. In addition,the oxidation of soot is enhanced since the counter-swirlinjection forces the intense fuel-rich and soot containingspray core to penetrate into fresh air instead of replenishingthe rich regions in the head of the spray. Fuel accumulationalong the piston bowl wall decreases as an effect of thereduced penetration with counter-swirl injection. Altogether,this decreases the smoke emissions for low and intermediateengine loads. For the combustion system studied, counter-swirl rotation ofthe injector cannot decrease the smoke emissions at high engineload since the reduced spray penetration impairs the airutilization. Fast and efficient combustion at high loadrequires spray induced flame spread out into the squish region.Spray induced flow of cool fresh air from the bottom of thepiston bowl in towards the injector is also important for lowsoot formation rates. Co-swirl rotation of the injector reduces the airentrainment into the spray and increases the soot formation.The increased smoke and CO emissions with co-swirl injectionare also attributed to the excessively large fuel-rich regionsbuilt up against the piston bowl wall. Increased air swirl generally reduces smoke and COemissions. This is mainly an effect of enhanced burnout due tomore intense mixing after the end of fuel injection. Changes in smoke as an effect of injector rotation aregenerally accompanied with opposite, but relatively small,changes in NO. Fast and efficient burnout is important for lowsmoke emissions and this raises both the temperature andproduction of NO. NO production is strongly influenced by thein-cylinder conditions during the latter part of themixing-controlled combustion and in the beginning of theburnout. <b>Keywords:</b>diesel spray combustion, rotating injector,air swirl, air/fuel-mixing, soot, NO, CO, flame visualization,Chemkin modeling, soot deposition