Fuel Spray Simulation Research Articles

A one-way coupling approach for simulating in-nozzle flow and spray characteristics of a pressure-swirl atomizer

This article proposes a model framework coupling in-nozzle flow and external spray and presents its application to the simulation of a commercial pressure-swirl atomizer, focusing on the transient characteristics of the internal flow and subsequently the impact on the spray characteristics. High-fidelity in-nozzle simulation of the liquid–gas interactions is performed using the volume-of-fluid (VOF) method. Then, a corresponding Lagrangian simulation of sprays is performed where the parcels are injected using the information from the VOF predictions instead of phenomenological models. Both the internal flow and the spray are compared to the experimental data that are available in the literature, and satisfactory agreement is obtained in terms of the in-nozzle velocity, film thickness, and Sauter mean diameter. The effect of the different liquid properties and geometric features on the air–core formation, and consequently, on the spray characteristics have been obtained directly through spray simulation coupled with nozzle flow. As indicated by the Eulerian simulation results, the viscosity plays a key role in the formation of the air core, as the hollow-cone shape can degenerate into a solid cylindrical liquid jet under high viscosity conditions. Additionally, significantly distinct spray characteristics in terms of droplet velocity, mean diameter, and penetration were predicted depending on the formation of air core. Even if there is no stable air core in the nozzle, the spray is still discharged in a swirling motion. As opposed to the converging angle and orifice length, the nozzle diameter has a direct correlation with the formation of air core and spray atomization. This study implies that the in-nozzle flow field, which is usually ignored in fuel spray simulation, has a substantial impact on the spray characteristics and should be taken into account for design optimization by applying the developed one-way coupling approach.

Effects of different droplet dispersion modeling methods on diesel spray simulation in Eulerian-Lagrangian framework

The realistic prediction of spray dynamics and dispersion is one of the main tasks of the combustion simulations in diesel engines. Usually, droplet dispersion modeling accuracy can be improved by the development of turbulence models and stochastic dispersion models. Although droplet dispersion due to turbulence is an important phenomenon in high-velocity fuel sprays, studies on the effect of these models are relatively few. Among these studies, the influence of a common used stochastic dispersion model on spray dynamics is not well understood and the application of hybrid turbulence models to fuel spray simulation in the Eulerian-Lagrangian framework with two-way coupling is still at starting stage. In the present study, a better understanding of the effect of the stochastic model on spray dynamics can be obtained by using a statistical analysis of stochastic dispersion time and velocity of dispersed droplets. In order to assess the ability of the hybrid model to improve the radial spread and the inhomogenous distribution of small droplets produced by a high-pressure injector, a partially averaged Navier-Stokes (PANS) model is implemented in an open-source code OpenFOAM and is compared with an unsteady Reynolds averaged Navier-Stokes (RANS) model and a large eddy simulation (LES) model. The results show the importance of resolving large-scale turbulent structures on droplet dispersion modeling in high-velocity fuel spray simulation. The common stochastic dispersion model used in RANS developed for homogenous, isotropic turbulent flows leads to the non-physical dynamics and distribution of droplets and hence is not applicable to the droplet dispersion which is dominated by the non-stochastic motion of large-scale structures in free shear layers. Using PANS instead of RANS should improve the droplet dispersion modeling accuracy of high-velocity fuel sprays in the development of diesel engines with an advanced injection system.

Evaluation of a Scale-Resolving Methodology for the Multidimensional Simulation of GDI Sprays

The introduction of new emissions tests in real driving conditions (Real Driving Emissions—RDE) as well as of improved harmonized laboratory tests (World Harmonised Light Vehicle Test Procedure—WLTP) is going to dramatically cut down NOx and particulate matter emissions for new car models that are intended to be fully Euro 6d compliant from 2020 onwards. Due to the technical challenges related to exhaust gases’ aftertreatment in small-size diesel engines, the current powertrain development trend for light passenger cars is shifted towards the application of different degrees of electrification to highly optimized gasoline direct injection (GDI) engines. As such, the importance of reliable multidimensional computational tools for GDI engine optimization is rapidly increasing. In the present paper, we assess a hybrid scale-resolving turbulence modeling technique for GDI fuel spray simulation, based on the Engine Combustion Network “Spray G” standard test case. Aspects such as the comparison with Reynolds-averaged methods and the sensitivity to the spray model parameters are discussed, and strengths and uncertainties of the analyzed hybrid approach are pointed out. The outcomes of this study serve as a basis for the evaluation of scale-resolving turbulence modeling options for the development of next-generation directly injected thermal engines.

Development of a Reduced Biodiesel Surrogate Fuel Model for Multi-Dimensional Computational Fluid Dynamic Simulations

This work reports the development of a reduced biodiesel surrogate fuel model for multi-dimensional Computational Fluid Dynamic simulations. The model is derived using an integrated kinetic mechanism reduction scheme and the final chemistry comprises only 83 species. The model is well validated in zero-dimensional chemical kinetic calculations under a wide range of auto-ignition and jet-stirred reactor conditions. The fidelity of the model is also further assessed in two-dimensional simulations of a constant-volume combustion vessel with respect to the experimental results of soy-methyl ester combustion. The results obtained reveal that ignition delay, lift-off lengths and soot volume fractions are reasonably well replicated by the reduced model. Furthermore, the compositions of the reduced model are varied according to the saturation/unsaturation levels of various biodiesel feed-stocks, such as palm-methyl ester and sunflower-methyl ester. In this work, it is demonstrated that the reduced model can potentially be used as a universal surrogate fuel model to predict the reactivity of biodiesel feed-stocks with low degree of saturation (≤30%) in both kinetic and fuel spray simulations.

Review on Simulation of Non-reacting Fuel Spray

Marine diesel engines (MDEs) are interested due to their ability to generate high power and fuel economy. Nowadays, researchers are seeking different methods to develop the performance of MDEs. Fuels spray behavior has key role to improve of MDEs. Therefore, in the present paper, fundamental of non-reacting and non-evaporating fuel spray simulation are reviewed. For this purpose, recent works in this context are presented and after that, microscopic and macroscopic characteristics of non-reacting spray are described. Finally, the basic formulations of Eulerian-Lagrangian multiphase and different breakup models are presented.

Simulation of diesel spray combustion using LES and a multicomponent vapourisation model

Diesel spray and combustion in a constant-volume engine cylinder was simulated by a large eddy simulation (LES) approach coupling with a multicomponent vapourisation (MCV) modelling. The simulation focused on the inclusion of the interaction between fuel spray and gas-phase turbulence flow at the sub-grid scale. The LES was based on the dynamic structure sub-grid model, and an additional source term was added to the filtered momentum equation to account for the effect of drop motion on the gas-phase turbulence. The multicomponent drop vapourisation modelling was based on the continuous thermodynamics approach using a gamma distribution to describe the complex diesel fuel composition and was capable of predicting a more complex drop vapourisation process. The effect of gas-phase turbulence flow on the fuel drop vapourisation process was evaluated through the solution of the gas-phase moments of the distribution in the present LES framework. A non-evaporative spray in a constant-volume engine cylinder was first simulated to examine the behaviours of LES, in comparison with a Reynolds-averaged Navier–Stokes (RANS) simulation based on the RNG k–ϵ model. More realistic diesel spray structures and improved agreement on liquid penetration length with the corresponding experimental data were predicted by the LES, using a grid resolution close to that of RANS. A more comprehensive simulation of diesel spray and combustion in cylindrical combustor was also performed. Predicted distributions of soot particles were compared to the experimental image, and improved agreement with the experimental data was also observed by using the present LES and MCV models. Consequently, results of the present models proved that improved overall performance of the fuel spray simulation can be achieved by the LES without a significant increase in the computational load compared to the RANS.

Fuel Spray Simulation with Valve Motion of Injector for Gasoline Direct Injection Engine

Fuel Spray Simulation with Valve Motion of Injector for Gasoline Direct Injection Engine

粒子法を用いたマルチホールノズルの燃料噴霧シミュレーション

粒子法を用いたマルチホールノズルの燃料噴霧シミュレーション

Numerical Simulation of Non-reacting Diesel Fuel Sprays under Low Temperature Late Injection Operating Condition

Accurate simulations on combustion and emission characteristics of direct injection diesel engines are highly dependent on detailed prediction of equivalence ratio distribution inside the combustion chamber. In this study, Open-FOAM and Lib-ICE multi-dimensional CFD frameworks were used in order to model engine flow, liquid diesel fuel spray, break-up, evaporation and mixing. Simulations were conducted on the basis of experimental data from SANDIA optical engine. Initial simulation results showed tangible discrepancy with the experimental equivalence ratio data in distribution of fuel-rich zones. Investigations on three different injection angles in three different combustion chamber bowl geometries showed that cavitation phenomenon was most probably occurred in injector nozzle during the experiments. Onset of cavitation in injector nozzle internal flow can noticeably change the spray break-up length and cause asymmetric spray angle later inside the combustion chamber. Taking cavitation effects into account, simulations were performed by corrected values of spray break-up length and injection angle based on experimental injection pressure and nozzle orifice dimensions. Final spray simulations showed better agreement with experimental results for all of three bowl geometries. This enhanced accuracy of numerical prediction without unacceptable tuning of spray sub-model parameters.

Effects of grid alignment on modeling the spray and mixing process in direct injection diesel engines under non-reacting operating conditions

In the present study, the Lagrangian–Eulerian approach was applied in simulation of non-reacting high pressure diesel fuel injection process under different modes of engine operating conditions. Investigations were shown that if coarse commonly used polar Cartesian grids were applied in the engine calculations, highly deflected spray morphology would be resulted, leading to subsequent erroneous air–fuel mixing predictions. Interestingly, more accurate and grid independent results cannot necessarily be achieved by further grid refinement for the aforementioned polar Cartesian grid. This study focuses on the effects of the computational grid alignment and its essential role in regions near to the injector nozzle where the coupling of the Lagrangian liquid and the Eulerian gas flow approaches is critical. Enhanced and more realistic spray penetration, air–fuel mixing, equivalence ratio and scalar dissipation rate distributions were resulted by discretizing the computational grid aligned to the direction of the spray. With this regard, a novel conical grid alignment was introduced and applied in liquid fuel spray simulations of an optically accessible direct injection diesel engine under different operating conditions. Comparisons in terms of liquid and gaseous fuel distributions were made with conventional polar Cartesian grids and spray-oriented grid with the experimental data. It has been also shown that radial alignment of grids in the conical grid can effectively reduce unexpected numerical diffusions ensuring well-captured spray morphology, evolution and air–fuel mixing.

G0501005 外開弁式燃料噴射装置の噴霧解析

G0501005 外開弁式燃料噴射装置の噴霧解析

Short Spray Penetration for Direct Injection Gasoline Engines With Secondary-Drop-Breakup Simulation Integrated With Fuel-Breakup Simulation

Direct injection gasoline engines have both better engine power and fuel efficiency than port injection gasoline engines. However, direct injection gasoline engines also emit more particulate matter (PM) than port injection gasoline engines do. To decrease PM, fuel injectors with short spray penetration are required. More effective fuel injectors can be preliminarily designed by numerically simulating fuel spray. We previously developed a fuel-spray simulation. Both the fuel flow within the flow paths of an injector and the liquid column at the injector outlet were simulated by using a grid method. The liquid-column breakup was simulated by using a particle method. The motion of droplets within the air/fuel mixture (secondary-drop-breakup) region was calculated by using a discrete droplet model (DDM). In this study, we applied our fuel-spray simulation to sprays for the direct injection gasoline engines. Simulated spray penetrations agreed relatively well with measured spray penetrations. Velocity distributions at the outlet of three kinds of nozzles were plotted by using a histogram, and the relationship between the velocity distributions and spray penetrations was studied. We found that shrinking the high-speed region and making the velocity-distribution uniform were required for short spray penetration.

Secondary-Drop-Breakup Simulation Integrated With Fuel-Breakup Simulation Near Injector Outlet

The fuel spray of an injector for automobile engines contains multiscale free surfaces: liquid films formed at the fuel-injector outlet, ligaments generated by liquid-film breakup, and droplets generated from the ligaments within the secondary-drop-breakup region. To simulate these multiscale free surfaces, we developed a method that combines two types of simulation. The liquid-film breakup near the injector outlet was simulated by using a particle method, and the secondary-drop breakup after the liquid-film breakup was simulated by using a discrete droplet model (DDM). The injection conditions of DDM were the distributions of droplet diameters and velocities calculated in the liquid-film-breakup simulation. We applied our method to simulate the spray from a collision-type fuel injector. The simulated liquid-film breakup near the injector outlet and behavior of the secondary-drop breakup qualitatively agreed with measurements. Furthermore, the errors of the mean droplet diameters between the simulations and the measurements were less than 12%. This shows that our method is effective for fuel spray simulation.

Effect of Droplet Size and Atomization on Spray Formation: A Priori Study Using Large-Eddy Simulation

The paper is mainly focused to the vast number of researchers who work within direct injection (DI) engine fuel spray simulations. The most common simulation framework today within the community is the Reynolds Averaged Navier Stokes (RANS) approach together with the Lagrangian Particle Tracking (LPT) method. In fact, this study is one of the first studies where high resolution LES/LPT diesel spray modeling is considered. The potential of LES to deepen the present day multidimensional LPT fuel spray simulations is discussed. Spray evolution is studied far from an injector by modeling a spray as a particle laden jet (PLJ). The effect of d on mixing in non-atomizing and atomizing sprays is thoroughly investigated at jet inlet Reynolds number Re = 104 and Mach number Ma = 0.3. Based on and justified by rather recent and also quite old ideas, novel and compact views on droplet breakup in turbulentflows are pointed out from the literature. We use LES/LPT to illustrate that even in a low Weber number flow (We < 13) the droplet breakup modeling may need considerable attention in contrast to what is typically assumed in the present-day breakup models. LES and LPT techniques are first applied to essentially confirm certain expected droplet size effects on spray shape in non-atomizing monodisperse sprays. In the simulations LES e.g. produces an expected turbulent dispersion pattern that depends on droplet diameter (d) without a droplet dispersion model in contrast to RANS. A new compact droplet breakup model is formulated and tested for droplets that break with a natural resonance time rate according to the Poisson process. As a result of the study: 1) the analysis gives a rigorous and enriching proof of currently existing views on droplet size effects on mixing, and 2) the presented a priori analysis points out the importance of modeling the resonance breakup even at a low We.

自動車用インジェクタの燃料噴霧・混合気一貫解析

The fuel spray contains multi-scale free surfaces; liquid films formed at the fuel-injector outlet, ligaments generated by the liquid-film breakup, and droplets generated from the ligaments within air/fuel mixture region. In order to simulate the multi-scale free surfaces, we previously developed a fuel spray simulation combining the liquid-film breakup near the injector outlet with the air/fuel mixture. In the air/fuel mixture simulation, droplet-motions were calculated by using Discrete Droplet Model (DDM). Distributions of droplet diameters and velocities, calculated in liquid-film breakup simulation, were used as an injection condition of DDM. We apply our method to simulate fuel sprays from two kinds of fuel injectors: a multi-hole fuel injector and a collision fuel injector. The simulation results are compared with the measurements. The spray distributions qualitatively agree well with measurements. We also study the effects of injection condition of DDM on the fuel spray from collision fuel injector; some sets of velocity and diameter distributions of droplets are simulated. It is found that the diameter distribution of droplets near the injector outlet mainly affects the leading edge of spray.

燃料噴射装置近傍の液膜分裂挙動を考慮した混合気解析(流体工学,流体機械)

The fuel spray for automobile engine includes multi-scale free surfaces; liquid films formed at the fuel-injector outlet, ligaments generated by the liquid-film breakup, and droplets generated from the ligaments within air/fuel mixture region. To simulate multi-scale free surfaces in the fuel spray of an injector for automobile engine, we combined a liquid-film-breakup simulation and an air/fuel-mixture simulation. The liquid-film breakup near the injector outlet was simulated by using a particle method, and the air/fuel mixture after the liquid-film breakup was simulated by using a "discrete droplet model" (DDM). Distributions of droplet diameters and velocities, calculated in the liquid-film breakup simulation, were used as the injection condition of DDM. We applied our new method to simulate the spray from a collision fuel injector. The simulation results were verified by comparing them with measurements. The liquid-film breakup near the injector outlet and the behavior of the air/fuel mixture qualitatively agreed with the measurements. We found that our new method was useful to the fuel-spray simulation for automobile engines.

Diesel and Biodiesel Fuel Spray Simulations

This paper deals with the investigation of the influential parameters of a mathematical spray breakup model using different fuels. Beside injection system measurements, fuel physical properties and injection process characteristics were measured, because they are necessary for the spray simulation input. For validation purposes, spray was injected into motionless air at atmospheric pressure and room temperature and filmed with a high-speed camera. Spray macrocharacteristics have been determined on the recorded images. Using the simulation program, the injection processes for diesel, biodiesel, and their 50% blend B50 have been simulated. Spray mathematical model parameters were tuned based on the experimentally gained results. Primary breakup model parameters showed the biggest impact on the spray characteristics and were therefore expressed using the fuel physical properties, the injection process characteristics, and the working regime parameters. Spray simulations into the combustion chamber were made in the end. All of these results are presented and discussed in this paper.