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Effects of droplet diameter, liquid and vaporized fuel concentration on the ignitability of fuel spray were investigated. A large number of ignition trials of various methanol liqui/vapor/air mixture were carried out. As a result, ignition probability increases with the increase of the liquid and vaporized fuel concentration and decreases with the increase of droplet diameter. The particular condition exists which fuel spray is not always ignited successfully even if the total fuel concentration is higher than that of lean ignition limit of vaporized fuel. In addition, simple probabilisticignition model that based on the fluctuation of spray concentration is applicable for macroscopic evaluation of ignition phenomenon. However, from the result of instantaneous liquid fuel concentration measurement, the assumption of probabilistic model, i. e., ignition is deterministic by the instantaneous liquid fuel concentration just befor ignited, is not adequate for microscopic evaluation.

This study attempts to prepare a fluid pair for use in spray dynamics investigations. Better understanding the behavior of fuel sprays is one of the things that can help improve the efficiency of internal combustion engines. To address the scattering issue in current imaging methods, the refractive index difference between the injected fluid and the medium that it is injected into is eliminated. Two immiscible fluids (sucrose solution and silicone oil) with the same refractive index was identified, their surface tension to build a model fluid engine system injection was also studied. At the same time, Weber number is found to help correct the difference. Results show that 63.7% mass sucrose solution has the same refractive index as silicone oil, and the sucrose solution/silicone oil interface has a surface tension of 0.08941 N/m, which is roughly four times larger than that of ethanol/air. This means using the sucrose/silicone oil fluid pair to model fuel spray will involve some adjustments to be accurate.

A state-of-the-art spray modeling methodology, recently presented by Senecal et al. [1, 2, 3], is applied to Large Eddy Simulations (LES) of vaporizing sprays. Simulations of non-combusting Spray H (n-heptane fuel) from the Engine Combustion Network are performed. Adaptive Mesh Refinement (AMR) cell sizes of 0.03125 mm to 0.25 mm are utilized to further demonstrate grid convergence of the Dynamic Structure LES model for diesel sprays. Twenty-eight different realizations are simulated by changing the random number seed used in the spray submodels. Multi-realization (ensemble) averaging, which has been shown to be necessary when comparing to local spray measurements, is performed. Global quantities such as liquid and vapor penetration are compared, as well as local mean mixture fraction and mixture fraction standard deviation. The results suggest that the current model does a reasonable job predicting the major features of the n-heptane spray when appropriate grid resolution is utilized.

The behaviors of laser-induced plasma and fuel spray were investigated by visualizing images with an ultra-high-speed camera. Time-series images of laser-induced plasma in a transient spray were visualized using a high-speed color camera. The effects of a shockwave generated from the laser-induced plasma on the evaporated spray behavior were investigated. The interaction between a single droplet and the laser-induced plasma was investigated using a single droplet levitated by an ultrasonic levitator. Two main conclusions were drawn from these experiments: (1) the fuel droplets in the spray were dispersed by the shockwave generated from the laser-induced plasma; and (2) the plasma position may have shifted due to breakdown of the droplet surface and the lens effect of droplets.

This study is dealing with a simplified attempt for evaporation process of multi-component fuel sprays. KIVA-II scheme was used as a multi-dimensional numerical code. And new conceptual model on multi-component fuel spray evaporation was proposed based on a simplified approach of two-phase region in vapor-liquid equilibrium. In the model, 50% distillation temperature of each component fuel was applied into evaporation process of multi-component solution, instead of precise estimation of two-phase region characteristics. Then, spatial vapor distributions of each fuel component were assessed from this model calculation in KIVA-II scheme.

The effects of in-cylinder charge motion, fuel spray characteristics and piston crown geometry on WOT output of a direct-injection gasoline engine were investigated. The mixture formation process in the cylinder was analyzed by computer simulation and LIF visualization. The results made clear the technical factors for achieving sufficient fuel–air mixing in a DI gasoline engine with a bowl-in-piston geometry optimized for stratified charge combustion.

One of the important research for developing a spark-ignited direct injection engine is optimization of the fuel spray distribution and air flow field in the cylinder. Therefore, spray pattern and mean fuel droplet size of swirl injector were investigated using Laser Light Sheet Photography and PDPA' respectively. And, for the formation of stratified mixture with adequate strength near a spark plug at injection mode in compression stroke, spray distribution after impingement on flat piston or bowl piston in a transparent motoring engine was visualized for the three different injector positions.

High-pressure diesel fuel sprays and their internal structure are observed using a novel visualization technique based on laser-induced fluorescence (LIF). A synchronization system is developed to control the timings of fuel injection, laser emission and image acquisition so as to capture spray images at an arbitrary stage of their developing process. Greatly magnified images of fluorescence dye, Rhodamine B, are taken and the internal velocities of fuel spray are measured by PIV in the core of the spray. The results show that branch-like structures are clearly visualized and diesel spray droplets exist along them. Fuel spray droplets are rapidly decelerated from about 300 m/s to 3-6 m/s at a time 4 ms after the injection.

To decrease exhaust emissions is crucial demand nowadays, especially decrease in smoke level at late injection timings is important when intending to decrease nitrogen oxides. In this study, an effectiveness of multiple spray plumes injected near by nozzle holes on the combustion characteristics was investigated using a quiescent chamber diesel engine, aiming to improve mixture formation and combustion by the cooperative action between spray plumes under conventional fuel supply pressure. As a result, it was found that the shorter the distance between nozzle holes and the larger the diameter of nozzle holes brought more intense promotion of combustion, enabling smoke level to decrease to half of that of standard nozzle, while no decrease in power output of the engine was identified.

Three dimensional computations were carried out to study the effects of engine operating conditions on NOx emissions from premixed lean diesel combustion in a DI engine. A modified KIVA II computer code was used to the numerical simulation. Qualitatively good agreement between computational and experimental results for impinging fuel spray shape, heat release rate and relative NOx mass has been achieved. The computational results demonstrate that NOx emissions are significantly influenced by temperature of intake air, fuel injection timing, and fuel ignitability. It is also indicated that fuel droplets gathered into the squish region are possible to become unburned fuel emissions.

Interest is growing in the benefits of homogeneous charge compression ignition engines. In this paper, we investigate a novel approach to the development of a homogenous charge-like environment through the use of porous media. The primary purpose of the media is to enhance the spread as well as the evaporation process of the high pressure fuel spray to achieve charge homogenization. In this paper, we show through high speed visualizations of both cold and hot spray events, how porous media interactions can give rise to greater fuel air mixing and what role system pressure and temperature plays in further enhancing this process.

Vbrizgavanje curka goriva spada na področje dvofaznih tokov, ki obravnava karakteristike curka goriva v odvisnosti od fizikalnih lastnosti, s poudarkom na vbrizgavanju različnih goriv, pod različnimi delovnimi pogoji. Poleg ocene kvalitete tvorbe zmesi je raziskovanje karakteristik curka goriva pomembno tudi za oceno izkoriščenosti zraka v zgorevalni komori in zaradi morebitnega nezaželenega stika goriva s stenami zgorevalne komore. Obstoječi fizikalno-matematični modeli lahko v splošnem relativno natančno popišejo razmere dvofaznega toka. V samih podmodelih so prisotne empirične konstante (vplivni parametri), s pomočjo katerih se uravnavajo karakteristike vbrizganega curka in ki so v osnovi odvisne od lastnosti samega vbrizgalnega sistema, predvsem od geometrije vbrizgalne šobe. V okviru naloge bo vpeljan model, ki bo omogočal obravnavanje karakteristik različnih biogoriv, razmer v šobi in posledice vpliva karakteristik na razvoj, obliko in strukturo curka, kjer bo omogočeno natančnejše analiziranje dvofaznih tokov. Model bo zajemal prenosne enačbe za številsko gostoto parnih mehurčkov, z upoštevanjem fizikalnih procesov nastajanja in izginjanja posameznih mehurčkov, pri različnih oblikah kavitacijskih tokov, hkrati pa bo omogočal še raziskavo vpliva med kapljicami goriva ter obravnavo sil trka z vpeljavo velikostne porazdelitve kapljic goriva. Naloga je razdeljena na eksperimentalni in numerični del. V eksperimentalnem delu so določene in analizirane fizikalne lastnosti uporabljenih goriv, karakteristike procesa vbrizgavanja, s pomočjo hitre kamere pa je bil posnet razvoj curka goriva. V numeričnem delu je prikazan osnovni poenostavljeni fizikalno-matematični model. V disertaciji je pokazano, da je mogoče s spremembo fizikalno-matematičnega modela, ob upoštevanju fizikalnih lastnosti goriva, delovnega režima in karakteristik procesa vbrizgavanja, določiti konstante, ki pri izračunu uravnavajo karakteristike curka goriva. S pomočjo ustreznih izrazov je tako mogoče izraziti empirične vrednosti parametrov in vnaprej napovedati probleme, ki bi se lahko pojavili v dizelskih motorjih z uporabo biogoriv. Fuel spray investigations belong to the field of the two-phase flows witch presents the study of physical fuel property dependent spray characteristics. The research will be focused on different type of fuels under different operating conditions. The investigation of spray development as contributing factor in mixture formation is also very important for the study of processes in internal combustion engine. Existing physical-mathematical model for two phase flows generally gives good results. Several empirical constants are present in sub models and they have significant influence on spray development. They are usually depended on injection system and the geometry of injection nozzle. The improvement of physical-mathematical model including the most influential factors with in the momentum equation for spray development, will enable efficient analysis of spray characteristics of alternative fuels. The model will also include the equations for bubble density and the equation for cavitation occurrence. The parts of equation representing the spray development, formation of bubbles and cavitation will be modelled with the adaptation of knowledge of other authors, where the modified model will be able to predict the spray development more accurately. The work contains both experimental and numerical part. Physical properties of the fuels, characteristics of the fuel injection process and high-speed recordings are described and analysed in the experimental part. The simplified physical-mathematical models is presented in the numerical part. The dissertation shows, that the improvement of standard mathematical model for spray development considering the physical fuel properties, the operating conditions and the injection characteristics enables determination of empirical constants. Additionally the physical-mathematical model can be included. By using of appropriate expressions, the empirical parameters values can be determined and enable predictions of potential problems which could appear in diesel engines during operation with biofuels.

To realize clean diesel exhaust, it is very important to clarify the atomization phenomena of the fuel spray. In this study, the initial stage of the atomization process of a diesel injection fuel spray was analyzed with a high-speed image converter camera under the conditions of atmospheric gas pressure and room temperature. As a result, it was found that the initial spray formation was greatly affected by the condition inside the nozzle sac. In the case in which fuel existed in the sac, pin-like structure spray formation was observed at the initial injection stage. This phenomenon was not observed in the case in which no fuel was present in the sac, and a widely spread fuel spray formation was observed at the initial injection stage. The relatively low speed fuel spray injected in the initial low-sac-pressure condition was pushed away by the subsequent fuel spray injected in the high-sac-pressure condition.

The spatial and temporal distribution of a fuel spray in a diesel engine has a determining effect on noise and exhaust emissions, fuel consumption, and engine performance (Battistoni and Grimaldi 2012; Kuti et al. 2013; Park et al. 2008). The most important fuel spray characteristics are spray penetration, spray angle, and Sauter mean diameter. These characteristics depend to a great extent on the injector type, fuel composition, and engine operating regime (Kousoulidou et al. 2012; Lin and Lin 2011; Mancauruso et al. 2011).

The study of transient high pressure fuel sprays by X-ray based techniques is worldwide diffused. Synchrotron radiation is successfully exploited for this aim because of its high intensity and pulsed nature. However top-table application are unusual. This work reports the structure of a gasoline spray from an automotive GDI injection system obtained by X-ray Tomography desktop experiments using an 8 keV Cu K? X-ray. Polycapillary semilens shaped the divergent X-ray beam into quasi-parallel one allowing to focus the radiation on the investigated spray region. High contrast focus images were collected by a CCD detector for X-radiation. A 6-hole GDI injector has been coupled to the high pressure pump by a specially designed rotating device able to work up to 25MPa. X-ray absorption measurements have been performed with angular steps ?? = 1° at the injection pressure of 12.0 MPa. The sinogram reconstruction of the jets by slices permitted to get information about the inner structure of the fuel spray downstream the nozzle tip, where conventional optical techniques are inhibited. A 3D spatial distribution of the fuel emerging from the injector has been obtained. The data have been used to perform spray density measurements. The results concerning the absorption profile along the fuel jets axis and the cross section distribution at different distances from the nozzle have been reported.

In the present paper we applied two well- known analytical method to the problem of thermal explosion of monodisperse and polydisperse fuel spray. The methods are the method of integral manifold (MIM) and the homotopy analysis method (HAM). The MIM method used as a basic tools for the analysis of SPS system of ordinary differential equations which means that the physical/ mathematical model should contain a small parameter in the governing equations. The HAM is always valid no matter whether there exist small physical parameters or not in contrast to the classical perturbation methods which requires the existence of a small parameter in the system (in general this is not the case). According to the theory of HAM, the convergence and the rate of solution series are dependent on the convergent control parameter h. This means that this parameter gives one a convenient way to adjust and to control the convergent region of the solutions.

The paper presents selected results concerning fuel charging and spraying process for selected alternative fuels, including regular diesel fuel, rape oil, FAME, blends of these fuels in various proportions, and blends of rape oil with diesel fuel. Examination of the process included the fuel charge measurements. To this end, a set-up for examination of Common Rail-type injection systems was used constructed on the basis of Bosch EPS-815 test bench, from which the high-pressure pump drive system was adopted. For tests concerning the spraying process, a visualisation chamber with constant volume was utilised. The fuel spray development was registered with the use of VisioScope (AVL).

The near-nozzle characteristics of a transient fuel spray were investigated via the measurement of drop sizes and velocities, and microphotographs of the near-nozzle region for a range of gas-to-liquid density ratios. In addition, a steady-state single-phase hydrodynamic simulation of the internal nozzle flow was performed to observe the effects of needle position on the internal flow. Measurement of droplet size and velocity near the nozzle on the edge of the spray showed that the average droplet velocity peaked during needle opening and needle closing, and changed throughout the spray event. Drop sizes tended to be small on the spray edge. Microphotographs of the near-nozzle region showed that the spray was most widely dispersed immediately after injection begins, narrowing rapidly to a constant spray angle. The same behavior was observed even for injection into near-vacuum conditions. However, once the spray was established, aerodynamic interactions were necessary for near-nozzle atomization.

The experimental and theoretical analyses of fuel spray motion in a side-injection combustion system, which is used to control fuel spray motion with air swirl for dynamic fuel-air mixture formation, were shown in this paper. Experimental studies on the fuel spray motion with air swirl in a constant-volume test rig by means of high-speed photographic observation, and theoretical analyses of fuel spray motion in a combustion chamber using CFD multi-dimensional model, and of fuel velocity, spray motion in a combustion chamber using CFD multi-dimensional model, and of fuel velocity, spray trajectory, and excess air ratio in the fuel spray were carried out. From these studies, important results on the characteristics of fuel spray motion and dispersion in side-injection combustion systems were obtained and the usefulness of CFD multi-dimensional analysis for improving spray dispersion in the combustion chamber was shown.

A three-dimensional diffusing spray using the multi-impingement-wall head (MIW head) has been proposed to form air-fuel mixtures in a single DI diesel engine. In this study, the effect of the width of the MIW head on spray pattern, distribution and engine performance have been investigated. In the fuel spray and engine performance experiments, an optimal width of the MIW head results in the collision of fuel droplets at an advantageous position in the combustion chamber for obtaining a good fuel spray distribution. The minimum BSFC is almost the same value as that of a single DI diesel engine, the HC and smoke densities are reduced and the NOx density show a tendency to increase under partial load and to decrease under full load. A relatively slow heat-release rate and maximum temperature duration of the MIW head can be obtained by shortening the ignition delay.

The atomization behavior of an intermittent fuel spray from a diesel nozzle was clearly observed by means of shadowgraphy using an image-converting camera with the framing rate of 105 f.p.s. and an image-intensified CCD camera with high-speed gating. A rather wide range of valve-opening pressure (5 to 70 MPa) was covered, and simultaneous measurement of the injection pressure inside the nozzle sac was also attempted to clarify the atomization mechanisms at its very early stage of injection. At the beginning of injection, the emergence of a liquid column was observed. Initially, it has almost the same diameter as the nozzle hole and then spreads radially, forming the spray angle in the vicinity of the nozzle exit. The timing of this spray-angle formation becomes earlier with the increase in valve opening pressure, even if the pressure inside the nozzle sac at this moment does not vary. This pressure approximately corresponds to that of the transition region in an atomization regime of a steady jet.

Optical Visualization system was applied to record images of the processes of spray, mixed gas formation and combustion in a homogenous GDI engine. Fuel spray was optimized by visual analysis of the images, thus improved the quality of mixed gas and combustion in the cylinder, it can provide the reference for injector selection and EMS calibration.

This study aims to investigate the combustion process and soot formation in diesel combustion with main/after injection. Heat release rates and high-speed photographs of luminous flame were analyzed changing injection interval and after-injection quantity using a constant volume vessel equipped with a multi-hole nozzle. The results show that luminous flame is still observed in the later stage of combustion for longer injection interval. Luminous flame decays earlier as the quantity of after injection decreases. With the lowest quantity of after injection, luminous flame disappears earlier than in the case of single injection., 日本機械学会2012年度年次大会 2012.9.9-12

One of the certification requirements that a jet engine has to fulfil is its altitude relight capability. Relighting an aero gas turbine engine at high altitudes is more challenging than at sea level conditions. The pressure, air velocity, and temperature within the combustor at such conditions are very low, hindering the fuel atomization and evaporation process. After ignition, combustion efficiency can be relatively low due to the poor fuel atomization quality, leading to slow shaft acceleration rates. Further studies in this field can help determine and predict the fuel spray characteristics, which limit the relight and pull-away capability of the engine at these sub-idle conditions. Reported in this paper is the CFD analysis of a typical airblast atomizer, simulated at different sub-idle operating conditions. Two sets of models were used; one with a simple liner-only combustor with co-flow air, and the other with a more detailed geometry, including wall cooling slots, primary and secondary dil...

This paper discusses the influence of biodiesel on the injection, spray, and engine characteristics with the aim to reduce harmful emissions. The considered engine is a bus diesel engine with injection M system. The injection, fuel spray, and engine characteristics, obtained with biodiesel, are compared to those obtained with mineral diesel under peak torque and ratedconditions. The considered fuel is neat biodiesel from rapeseed oil. Its density, viscosity, surface tension, and sound velocity are determined experimentally and compared to those of mineral diesel. The experimentally obtained results are used to analyze the most important injection, fuel spray, and engine characteristics. Furthermore, the influence of biodiesel usage on lubrication is presented briefly. The results indicate that, by using biodiesel, harmful emissions (NOx, CO, HC, smoke, and PM) can be reduced to some extent by adjusting the injection pump timing properly while keeping other engine characteristics within acceptable limits. Furthermore, the results indicate better lubrication conditions when biodiesel is used.

The Flamelet Generated Manifold (FGM) method is a promising technique in engine combustion modeling to include tabulated chemistry. Different methodologies can be used for the generation of the manifold. Two approaches, based on igniting counterflow diffusion flamelets (ICDF) and homogeneous reactors (HR) are implemented and compared with Engine Combustion Network (ECN) experimental database for the baseline n-heptane case. Before analyzing the combustion results, the spray model is optimized after performing a sensitivity study with respect to turbulence models, cell sizes and time steps. The standard High Reynolds ( Re ) k-e model leads to the best match of all turbulence models with the experimental data. For the convergence of the mixture fraction field an appropriate cell size is found to be smaller than that for an adequate spray penetration length which appears to be less influenced by the cell size. With the optimized settings, auto-ignition and flame lift-off length are analyzed. In general, both techniques capture the qualitative trend of experimental results. However, typically, the HR tabulation method predicts shorter ignition delay and LOL results than the ICDF method. In a quantitative sense, the ICDF and HR methods give better results in LOL and auto-ignition predictions, respectively.

The glycerine combustion is very problematic and difficult realizable because of its bad physical and chemical properties. The aim of article is measuring and evaluation of concentration of non-limited harmful pollutants during glycerine combustion in experimental burner. The main dangerous emissions which were measured were concentrations of acrolein and formaldehyde. The combustion from chemical aspect is fuel oxidation which can perform in any temperature. Glycerine combustion is very problematic and complicated due to its high viscosity, low pressure of vapour, high temperature of auto-ignition, and fears from production of dangerous emissions. The main dangerous emissions are aldehydes and ketones. The main representatives of aldehydes are formaldehyde and acrolein. Antecedent attempts showed that the most suitable means for glycerine combustion was burner usage. The burner has to be modified to be able to effective work with this type of fuel. The most important process during glycerine combustion in burner is fuel atomization. Three types of burner nozzle for glycerine were tested for glycerine atomization. Each with the same standardized capacity, same fuel spray angle. But the spray pattern was different. The nozzles had hollow, semi-solid, and solid spray pattern. Influence of spray pattern was surveyed. 2. EXPERIMENTAL BURNER Experimental burner for glycerine combustion was two-fuel axial swirl burner with mechanical principle of glycerine atomization. It contained two fuel lines, for glycerine and for supporting fuel. The supporting fuel was gaseous propane-butane. The supporting fuel had to heat up the combustion chamber (about 300°C) before injection of glycerine and stabilize glycerine combustion. Problems with high viscosity of glycerine were eliminated by means of preheating. Preheating reduced viscosity of glycerine and improved fuel processing. The fuel line for glycerine contained two preheaters, first preheater was in fuel tank, and second was before fuel nozzle. Second preheater was integrated into compact nozzle holder body and preheated glycerine to temperature 90°C.

Simulations of gas turbine combustors are sensitive to fuel boundary conditions and therefore accurate predictions of combustor performance rely on successful modeling of the fuel spray. Atomization models for a realistic, pressure swirl atomizer used in an aircraft gas turbine combustor are investigated to correctly predict the atomizer’s performance. A complex interaction exists between the fuel spray and surrounding air used to promote atomization. WAVE and stochastic secondary breakup models are used to model this interaction. Experimental characterization of this atomizer has been previously performed and the results of this experiment were used to evaluate numerical simulations. Qualitative comparisons of the simulation and experimental results show the stochastic breakup model correctly predicts the spatial distributions of fuel velocity and drop size.

The aim of the present work is the investigation of the combustion phenomenon in liquid-propellant rocket engines. The combustion of liquid oxygen and gaseous methane in a shear coaxial injector under supercritical pressure was analyzed. To realize an efficient numerical description of the phenomena, it is important to treat the LOx jet in a manner which takes into account its real behavior. In the present work different kinetics, combustion models and thermodynamics approaches were used in association with the description of the jet as a discrete phase. For all the approaches used, a comparison with experimental data from literature was performed. Copyright © 2012 by ASME.

In this work, a numerical study has been performed to evaluate the fuel spray of diesel, dimethyl ether (DME) and its mixture using CFD code OpenFoam. This study uses a general method, based on simulating fuel sprays injected into a constant volume vessel. Calculations results are presented as profiles of diameter (MD) and temperature of fuel droplets as function of fuel type. The results have shown that the diameter of fuel droplet decreased as the fraction of DME in the mixture is higher. Fuel properties affected the atomization and evaporation process. The SMD increased with viscosity and the evaporation rate of fuel spray increased with fuel volatility.