Bowl Geometry Research Articles

Modified bowl geometry for cluster nozzles in direct-injection diesel engines

A combination of high-pressure injection and small orifices will be one of the strategies to achieve lean combustion. However, equispaced small orifices tend to increase soot under high-load conditions because the spray penetration becomes exceedingly inadequate. For this reason, the cluster concept was chosen as the means to realize lean combustion. To make the use of clusters in a diesel engine feasible, a significant redesign of the typical in-cylinder geometry would probably be required to promote efficient air utilization. The new combustion chamber was designed with a smaller diameter and deeper bowl. It is expected to improve fuel—air mixing by better spray guidance. The study identifies the aspects of combustion and pollution formation that are affected by mixing processes and offers guidance for better matching of the piston geometry with the spray plume geometry for enhanced mixing. Various clusters were investigated to achieve variation in the injection timing for different test points in the original piston bowl chamber and the new bowl chamber, and the results are compared with those for a conventional nozzle. The cluster with the best results for smoke emissions in the first set of tests was also tested for different swirl ratios and different nozzle protrusion lengths.

Assessment of Multiobjective Genetic Algorithms With Different Niching Strategies and Regression Methods for Engine Optimization and Design

In a previous study (Shi, Y., and Reitz, R. D., 2008, “Assessment of Optimization Methodologies to Study the Effects of Bowl Geometry, Spray Targeting and Swirl Ratio for a Heavy-Duty Diesel Engine Operated at High-Load,” SAE Paper No. 2008-01-0949), nondominated sorting genetic algorithm II (NSGA II) (Deb, K., Pratap, A., Agarwal, S., and Meyarivan, T., 2002, “A Fast and Elitist Multiobjective Genetic Algorithm: NSGA-II,” IEEE Trans. Evol. Comput., 6, pp. 182–197) performed better than other popular multiobjective genetic algorithms (MOGAs) in engine optimization that sought optimal combinations of the piston bowl geometry, spray targeting, and swirl ratio. NSGA II is further studied in this paper using different niching strategies that are applied to the objective space and design space, which diversify the optimal objectives and design parameters, accordingly. Convergence and diversity metrics are defined to assess the performance of NSGA II using different niching strategies. It was found that use of design niching achieved more diversified results with respect to design parameters, as expected. Regression was then conducted on the design data sets that were obtained from the optimizations with two niching strategies. Four regression methods, including K-nearest neighbors (KNs), kriging (KR), neural networks (NNs), and radial basis functions (RBFs), were compared. The results showed that the data set obtained from optimization with objective niching provided a more fitted learning space for the regression methods. KNs and KR outperformed the other two methods with respect to prediction accuracy. Furthermore, a log transformation to the objective space improved the prediction accuracy for the KN, KR, and NN methods, except the RBF method. The results indicate that it is appropriate to use a regression tool to partly replace the actual CFD evaluation tool in engine optimization designs using the genetic algorithm. This hybrid mode saves computational resources (processors) without losing optimal accuracy. A design of experiment (DoE) method (the optimal Latin hypercube method) was also used to generate a data set for the regression processes. However, the predicted results were much less reliable than the results that were learned using the dynamically increasing data sets from the NSGA II generations. Applying the dynamical learning strategy during the optimization processes allows computationally expensive CFD evaluations to be partly replaced by evaluations using the regression techniques. The present study demonstrates the feasibility of applying the hybrid mode to engine optimization problems, and the conclusions can also extend to other optimization studies (numerical or experimental) that feature time-consuming evaluations and have highly nonlinear objective spaces.

Optimization of a high-speed direct-injection diesel engine at low-load operation using computational fluid dynamics with detailed chemistry and a multi-objective genetic algorithm

A passenger car high-speed direct-injection diesel engine operating at low-load conditions in the modulated kinetic combustion mode was optimized using a multi-dimensional computational fluid dynamics code and a multi-objective genetic algorithm. Spray targeting, piston bowl geometry, and swirl ratio were optimized. Since the combustion is mainly kinetics controlled, detailed chemistry was considered through a recently developed adaptive multi-grid chemistry (AMC) model. The numerical results from the AMC model, including the pressure and pollutant emissions, were first validated on the baseline engine for a parametric sweep by comparison with the results from the standard KIVA—CHEMKIN model. The AMC model was found to give consistent results with the KIVA—CHEMKIN model, with a computational cost that is less than half that of the KIVA—CHEMKIN model. Optimal designs from the optimization were also validated using the full KIVA—CHEMKIN model and were found to reduce the fuel consumption and/or pollutant emissions. Start-of-injection timing was found to be the primary parameter influencing the fuel consumption and soot emissions for the engine operating in the low-load condition. Later injection benefits the fuel consumption and soot reduction. However, further retardation of the injection timing leads to reduced combustion efficiency and even misfire, and results in higher unburned hydrocarbon emissions. Different piston bowl shapes have different responses to bulk flow motions and the resulting geometry-generated turbulence will affect soot formation and oxidation.

Investigation of piston bowl geometry and speed effects in a motored HSDI diesel engine using a CFD against a quasi-dimensional model

Abstract The present work investigates the effect of varying the combustion chamber geometry and engine rotational speed on the gas flow and temperature field, using a new quasi-dimensional engine simulation model in conjunction with an in-house developed computational fluid dynamics (CFD) code served to validate the predicted in-cylinder flow field and gas temperature distribution calculated by the quasi-dimensional model, for three alternative piston bowl geometries and three rotational speeds. This CFD code can simulate three-dimensional curvilinear domains using the finite volume method in a collocated grid; it solves the generalized transport equation for the conservation of mass, momentum and energy, and incorporates the standard k–e turbulence model with some slight modifications to introduce the compressibility of a fluid in generalized coordinates. On the other hand, the quasi-dimensional model solves the general transport equation for the conservation of mass and energy by a finite volume method throughout the entire in-cylinder volume, while for the estimation of the flow field a new simplified three dimensional air motion model is used. To compare these two models the in-cylinder spatial and temporal temperature distribution, the mean cylinder pressure diagram, as well as the mean in-cylinder radial and axial velocity are examined, for the three piston bowl geometries and the three speeds, for a high speed direct injection (HSDI) diesel engine operating under motoring conditions. From the comparison of calculated results, it becomes apparent that the two models predict similar in-cylinder temperature distributions and mean air velocity fields at each crank angle, for all cases examined. Thus, it is shown that the quasi-dimensional model with the proposed simplified air motion model is capable of capturing the physical effect of combustion chamber geometry and speed on the in-cylinder velocity and temperature field, while needing significantly lower computing time compared to the more detailed and accurate CFD model. On the other hand, the CFD model is more suitable when detailed simulation of the in-cylinder geometry is required and the way the corresponding transport phenomena are affected.

Applying an Interactively Coupled CFD-Multi-Zone Approach to Study the Effects of Piston Bowl Geometry Variations on PCCI Combustion

Applying an Interactively Coupled CFD-Multi-Zone Approach to Study the Effects of Piston Bowl Geometry Variations on PCCI Combustion

Influence of Injection Timing and Piston Bowl Geometry on PCCI Combustion and Emissions

Influence of Injection Timing and Piston Bowl Geometry on PCCI Combustion and Emissions

Low temperature premixed combustion within a small bore high speed direct injection (HSDI) optically accessible diesel engine using a retarded single injection

An optically accessible single-cylinder high speed direct-injection (HSDI) Diesel engine equipped with a Bosch common rail injection system was used to study low temperature Modulated Kinetics (MK) combustion with a retarded single main injection. High-speed liquid fuel Mie-scattering was employed to investigate the liquid distribution and evolution. By carefully setting up the optics, three-dimensional images of fuel spray were obtained from both the bottom of the piston and the side window. The NOx emissions were measured in the exhaust pipe. The influence of injection pressure and injection timing on liquid fuel evolution and combustion characteristics was studied under similar fuel quantities. Interesting spray development was seen from the side window images. Liquid impingement was found for all of the cases due to the small diameter of the piston bowl. The liquid fuel tip hits the bowl wall obliquely and spreads as a wall jet in the radial direction of the spray. Due to the bowl geometry, the fuel film moves back into the central part of the bowl, which enhances the air-fuel mixing process and prepares a more homogeneous air-fuel mixture. Stronger impingement was seen for high injection pressures. Injection timing had little effect on fuel impingement. No liquid fuel was seen before ignition, indicating premixed combustion for all the cases. High-speed combustion video was taken using the same frame rate. Ignition was seen to occur on or near the bowl wall in the vicinity of the spray tip, with the ignition delay being noticeably longer for lower injection pressure and later injection timing. The majority of the flame was confined to the bowl region throughout the combustion event. A more homogeneous and weaker flame was observed for higher injection pressures and later injection timing. The combustion structure also proves the mixing enhancement effect of the liquid fuel impingement. The results show that ultra-low sooting combustion is feasible in an HSDI diesel engine with a higher injection pressure, a higher EGR rate, or later injection timing, with little penalty on power output. It was also found that injection timing has more influence on HCCI-like combustion using a single main injection than the other two factors studied. Compared with the base cases, simultaneous reductions of soot and NOx were obtained by increasing EGR rate and retarding injection timing. By increasing injection pressure, NOx emissions were increased due to leaner and faster combustion with better air-fuel mixing. However, smoke emissions were significantly reduced with increased injection pressure.

Optimization study of the effects of bowl geometry, spray targeting, and swirl ratio for a heavy-duty diesel engine operated at low and high load

Optimization tools are used to recommend low-emission engine combustion chamber designs, spray targeting, and swirl ratio levels for a heavy-duty diesel engine operated at low load and high load. A non-dominated sorting genetic algorithm (NSGA II) was coupled with the KIVA computational fluid dynamics (CFD) code, as well as with an automated grid generation technique to conduct the multi-objective optimizations with goals of low emissions and improved fuel economy. The study identifies the aspects of the combustion and pollution formation that are affected by mixing, and offers guidance for better matching of the piston geometry with the spray plume geometry for enhanced mixing. By comparing the optimal results of low-load and high-load cases, the study reveals that different injection strategies and matching of the piston geometry with the spray plume are needed for different operating conditions. A non-parametric regression analysis tool was also used to post-process the optimized results in order to provide an understanding of the effects of each optimized parameter on fuel economy and pollutant formation. It was found that an optimal combination of spray targeting, swirl ratio, and bowl geometry exists that simultaneously minimizes emissions formation and offers improved fuel consumption.

Large Eddy Simulation and Experiments of the Auto-Ignition Process of Lean Ethanol/Air Mixture in HCCI Engines

Recent experiments and numerical studies have showed that piston geometry has a significant effect on the homogeneous charge compression ignition (HCCI) process. There are two effects generated by the combustor geometry: the geometry affects the flow/turbulence in the cylinder; the geometry also affects the temperature stratification. The temperature stratification is more directly responsible for the observed alteration of the auto-ignition process. To clarify this issue further we present in this paper a study of two engines with the same geometry but difference ways of cooling. Measurement of the two engines~a metal engine and quartz piston engine, both with the same piston bowl geometry~is carried out. Large eddy simulation (LES) is used to simulate the flow, the temperature field and the auto-ignition process in the two engines. The fuel is ethanol with a relative air/fuel ratio of 3.3. It is found that lower temperature stratification is established in the metal engine under similar conditions as the optical quartz engine due to the more effective cooling of the piston in the metal engine configuration. The combustion phasing in the two engines is the same by controlling the intake temperature. Both measurements and LES show a more rapid auto-ignition in the metal engine than in the optical engine with the same piston geometry. This confirms the conclusion that large temperature stratification can decrease the pressure-rise-rate and thereby increase the load of HCCI engines. The dependence of temperature stratification on the wall temperature and intake temperature is systematically studied using LES. (Less)

Effects of Piston Bowl Geometry on Mixture Development and Late-Injection Low-Temperature Combustion in a Heavy-Duty Diesel Engine

Effects of Piston Bowl Geometry on Mixture Development and Late-Injection Low-Temperature Combustion in a Heavy-Duty Diesel Engine

Assessment of Optimization Methodologies to Study the Effects of Bowl Geometry, Spray Targeting and Swirl Ratio for a Heavy-Duty Diesel Engine Operated at High-Load

Assessment of Optimization Methodologies to Study the Effects of Bowl Geometry, Spray Targeting and Swirl Ratio for a Heavy-Duty Diesel Engine Operated at High-Load

Validating the Phenomenological Smoke Model at Different Operating Conditions of DI Diesel Engines

A new phenomenological model that was published in Aghav et al. (2005, “Phenomenology of Smoke From Direct Injection Diesel Engines,” Proceedings of ICEF2005, ASME Paper No. 1350) encompasses the spray and the wall interaction by a simple geometrical consideration. The current study extends this earlier work with investigations made on 16 different engines from six-engine families of widely varying features, applied to off-highway as well as on-road duty. A dimensionless factor was introduced to take care of the nozzle hole manufactured by hydroerosion, as well as the conical shape of the nozzle hole (k factor) in the case of valve-closed-orifice type of nozzles. The smoke emitted from the wall spray formed after wall impingement is the major contributor to the total smoke at higher loads. As the fuel spray impinges upon the walls of the combustion chamber, its velocity decreases. This low-velocity jet contributes to the higher rate of the smoke production. Therefore, the combustion bowl geometry along with injection parameters play a significant role in the smoke emissions. The new model is one dimensional and based on the recent phenomenological description of spray combustion in a direct injection diesel engine. The satisfactory comparison of the predicted and observed smoke over the wide range of engine operation demonstrated applicability of the model in simulation study of combustion occurring in direct injection (DI) diesel engines.

Computational study of the sensitivity to ignition characteristics of the resonance in DI diesel engine combustion chambers

PurposeThe purpose of this computational fluid dynamics (CFD) study is to give insight about the influence of the piston bowl geometry and the fuel ignition features on the resonance of direct injection diesel engines combustion chambers in order to provide support to the experimental findings on combustion noise.Design/methodology/approachThe resonance due to the burned gases oscillations in a diesel combustion chamber is caused by the sudden rise in pressure due to the initial ignition of the air‐fuel mixture, and leads to the resonance noise. In the CFD study presented here the excitation source is represented by imposing locally in a small area (excitation zone) the pressure and temperature gradients of the start of combustion. The CFD approach is first validated against the acoustic modal theory. A parametric study representing different ignition conditions is then performed with a real bowl geometry.FindingsThe solutions obtained are analysed in terms of the energy of resonance (ER) and the response in the frequency domain. It was found that the response in frequency only varies with the diameter of the bowl, while the ER varies significantly in function of the injection conditions.Research limitations/implicationsThese first conclusions need to be verified on the one hand by taking into account the piston motion, and, on the other hand, by modelling in a more realistic way the combustion excitation.Practical implicationsThis CFD study has brought some insight into the flow phenomena that affect the resonance modes of a combustion chamber.Originality/valueThis CFD study uses a novel methodology to model the effect of the combustion excitation on the resonance modes of a combustion chamber.

Mixture Preparation and Combustion in an Optically-Accessible HCCI, Diesel Engine

Mixture Preparation and Combustion in an optically-accessible HCCI, Diesel EnginePlanar laser-induced fluorescence (LIF) imaging techniques have been applied in order to study the mixture preparation and combustion process in a single cylinder, optically-accessible homogeneous charge, compression ignition (HCCI) engine. In particular, the influence of piston bowl geometry on the in-cylinder mixture distribution and subsequent combustion process has been investigated. A new optically-accessible piston design enabled the application of LIF diagnostics directly within the combustion chamber bowl. Firstly, laser-induced exciplex fluorescence (LIEF) was exploited in order to characterise the in-cylinder fuel spray and vapour distribution. Subsequently a detailed study of the twostage CCI combustion process was conducted by a combination of direct chemiluminescence imaging, laser-induced fluorescence (LIF) of the intermediate species formaldehyde (CH2O) which is present during the cool flame and LIF of the OH radical which is subsequently present in the reaction and burned gas zones at higher temperature. Finally, spectrometry measurements were performed with the objective of determining the origin of the emitting species of the chemiluminescence signal. The experiments were performed on a single cylinder optical engine equipped with a direct-injection, common rail injection system and narrow angle injector. The experimental results presented reveal the significant role of the combustion chamber geometry on the mixture preparation and combustion characteristics for late HCCI injection strategies particularly in such cases where liquid impingement is unavoidable. Planar LIF 355 imaging revealed the presence of the intermediate species formaldehyde allowing the temporal and spatial detection of auto-ignition precursors prior to the signal observed by chemiluminescence in the early stages of the cool flame. Formaldehyde was then rapidly consumed at the start of main combustion which was marked not only by the increase in the main heat release but also by the first detection of OH, present within the reaction and burned gas zones. In the case of the flat piston geometry, soot precursors were also detected, as indicated by the strong polycyclic aromatic hydrocarbon (PAH) fluorescence signal observed later in the cycle (from 375 CAD).

Computational fluid dynamics study of the effects of the re-entrant lip shape and toroidal radii of piston bowl on a high-speed direct-injection diesel engine's performance and emissions

The piston bowl design is one of the most important factors that affect the air-fuel mixing and the subsequent combustion and pollutant formation processes in a direct-injection diesel engine. The bowl geometry and dimensions, such as the pip region, bowl lip area, and toroidal radius, are all known to have an effect on the in-cylinder mixing and combustion process. In order to understand better the effect of re-entrant geometry, three piston bowls with different toroidal radii and lip shapes were investigated using computational fluid dynamics engine modelling. KIVA3V with improved submodels was used to model the in-cylinder flows and combustion process, and it was validated on a high-speed direct-injection engine with a second-generation common-rail fuel injection system. The engine's performance, in-cylinder flow, and combustion, and emission characteristics were analysed at maximum power and maximum torque conditions and at part-load operating conditions. Three injector protrusions and injection timings were investigated at full-load and part-load conditions.

Computational study of the effects of the geometry of the piston bowl pip for a high-speed direct injection diesel engine

The piston bowl design is one of the most important factors that affect the air/fuel mixing and the subsequent combustion and pollutant formation processes in a direct injection diesel engine. The bowl geometry and dimensions, such as the pip region, the bowl lip area and the torus radius, are all known to have an effect on the in-cylinder mixing and combustion process. In order to understand better the effect of the pip region, three piston bowls with different pip designs but with the same lip area and torus radius were designed and investigated using computational fluid dynamics (CFD) engine modelling. A commercial CFD KIVA3V with improved submodels was used to model the in-cylinder flows and combustion process, and it was validated on a high-speed direct injection (HSDI) engine with a second-generation common rail fuel injection system. The engine performance, in-cylinder flow and combustion and emission characteristics were analysed at maximum power and maximum torque conditions and at part-load operating conditions. Three injector protrusions and injection timings were investigated at full load conditions. The effect of injection timing and exhaust gas recirculation (EGR) at the part-load condition was considered.

Combustion chamber resonances in direct injection automotive diesel engines: A numerical approach

The resonant oscillation of burned gases in the combustion chamber of direct injection (DI) diesel engines appears to be the main excitation source of the engine block during combustion. This has led to the application of different techniques in order to study its generation mechanisms and to determine its relationship with combustion parameters such as bowl geometry, type of injector, injection parameters, etc. In this paper, a numerical methodology for the analysis of combustion chamber resonances is proposed. The numerical approach is validated by comparison with results from modal theory in a simple case. Then, this technique has been applied to the analysis of three different bowls, indicating their potential for the control of combustion chamber resonances.

Improvement of the floc resistance to a centrifugal shear field by polymer adjunction

The hydrodynamic behaviour of suspended colloid aggregates is studied in three centrifugal separators. The experiments outline the effects of the residence-time duration and of the bowl geometry on the aggregate shear thinning. The floc destruction is stated either from the decrease of their average size d t with time, or from the production of microflocs, the statistical diameter of which, d MF , may be compiled from the floc size distribution. They both extend towards equilibrium values: d min, the final average size of the aggregates that depends on the shear rate, and d MF , the indestructible microfloc average diameter that may be considered as a physicochemical character. The equilibrium average sizes of the flocs as well as of the microflocs are reproducible at different geometric scales. Lastly, the kinetics of floc shear thinning might be approximated as a function of d min and d MF as was checked in the centrifugation tests of MnO 2 colloidal suspensions: d(d t) d t =k 2·d MF· 1−: d t d min Three different colloidal suspensions: MnO 2, Ru-Mo and dissolution juices of irradiated fuel are flocculated through hydrosoluble polymer addition. The comparisons of d min and d MF values measured for each initial suspension, then for the flocculated suspensions conclude that flocculant adjunction enables the improvement of the floc toughness to the shear rate, but also modifies their ordering into bigger and indestructible microflocs. Lastly, the obvious effect of the flocculant ionicity, observed on basic suspensions as well as on acid suspensions, claims that the nature of the acting interparticle forces entirely defines the aggregate structure and therefore their cohesion.

Application of centrifugal washing for fine-coal cleaning

Froth flotation is now the most commonly used method for cleaning fine-coal fractions in coal-preparation plants. Past research and industrial practice have demonstrated that froth flotation achieves excellent separation efficiencies for fine coals having only a small fraction of middling particles. However, the efficiency of froth flotation decreases sharply as the concentration of middling particles increases. This is due to the flotation of high-ash particles that have a small amount of hydrophobic coal present at the surface. Because gravity-based processes are much more efficient for the treatment of middlings, the application of centrifugal washing for fine-coal cleaning was studied with an emphasis on the primary cleaning of fine-circuit feed. Results are shown of a parametric study that used a semibatch Falcon centrifugal concentrator. The results of the study revealed that separation performance is a function of particle size, bowl geometry, feed solids content and feed rate.

A Study of the Falcon Concentrator

A B6 Falcon Concentrator was tested on several systems: a synthetic magnetite-silica ore, a massive sulphide gold–eopper ore, a fine gold-pyrite-silica flotation tail, and a high-grade gold ore in a low sulphide gangue (cyclone overflow).The Falcon demonstrated its ability to achieve separation in all cases, but with varying degrees of success. For the magnetite-silica system, separation proceeded until the concentrate bed overloaded, at a mass of 300–400 g of magnetite. Recovery increased with decreasing particle size, down to 25–37μm, and in some cases even below 25 μm. Bowl geometry (angle) and gangue size distribution were the most significant operating variables. Results with the massive sulphide ore were the poorest, with gold recoveries typically around 10–20% at very low upgrading ratios, 1:1–5:1. Gold recovery from the fine flotation tail ranged from 30 to 70% at upgrading ratios of 5–15. The high-grade gold cyclone overflow yielded a wide range of gold recoveries, with a very consistent relationship between recovery and mass processed. With a highgrade feed, a concentrate of 0.5% Au could be produced at a recovery of 50%. Résumé Un concentrateur Falcon, type B6, a été utilisé pour le traitement de plusieurs échantillons: un mélange synthétique de magnétite-silice, un minerai or et cuivre de sulfures massifs, un rejet de flottation très fin contenant de l'or, de la pyrite et de la silice, et un minerai d'or à haute teneur contenant peu de sulfures (sur-verse de cyclone).Le Falcon a pu enrichir les produits traités, avec plus ou moins de succès, selon le cas. Pour le mélange magnétite-silice, la séparation se poursuit tant que la bande de concentré n'est pas saturée, ce qui se produit lorsque de 300–400 g de magnétite ont été récupéré. La récupération augmente à mesure que la taille des particules de magnétite diminue, jusqu'à 25–37 μm, et même dans certains cas, le –25 μm. La géométrie du rotor et la granulométrie de la gangue sont les variables opératoires qui ont le plus d'effet sur la récupération. C'est le minerai de sulfures massifs qui a donné les pires résultats, soit des récupérations en or de 10–20%, et des rapports d'enrichissement très bas, variant de 1:1–5:1. Pour le rejet de flottation fin, de 30–70% de l'or fut récupéré, les rapports d'enrichissement variant entre 5:1 et 15:1. En traitant le minerai d'or à haute teneur, nous avons pu, en augmentant la masse traitée, augmenter la teneur du concentré, mais au prix d'une chute de la récupération. Le point d'opération optimum semblait être autour d'une teneur de concentré de 0.5% Au, qui pouvait être atteinte avec une récupération de 50% de l'or.