An investigation on the impact of small-scale models in gasoline direct injection sprays (ECN Spray G) (original) (raw)
Related papers
An Evaluation of Atomization Models for Dense Sprays
Calculations of a transient atomization process are presented, which simulates fuel injection of sprays in gasoline direct injection engines. Only non-reacting sprays are considered with the focus on the atomization process. The FIRE code, developed by AVL, is used as the platform to test three different atomization models: (i) Taylor Analogy Breakup (TAB) model; (ii) surface wave instability (WAVE) model; and the more recent (iii) FIPA (Fractionnement Induit Par Acceleration) model. Comparisons of calculations with experimental data reveal significant discrepancies regardless of the atomization model used. It is acknowledged that, in this study, only the standard model constants are adopted and that may be further optimised to improve the calculations. However, the fact remains that all the atomization models start with an initial distribution of spherical droplets at the injector tip. An assumption that is not supported by recent measurements which show that fluid elements rather than spherical droplets dominate this early zone.
Experimental investigation and modelling of diesel engine fuel spray
2008
9]. Under Lagrangian-Eulerian approach the spray is modelled as an ensemble of droplet parcels. Each parcel is characterised by its own droplet size, temperature and specified injection velocity. In some cases however the prediction can be worse than that by an empirical correlations or a simpler spray model [5]. This can be attributed to the intrinsic deficiency of the Lagrangian-Eulerian approach for dense sprays.
Journal of the Brazilian Society of Mechanical Sciences and Engineering
Direct injection plays an important role in the efforts to increase efficiency of modern engines, and the correct evaluation of the velocity and fuel mixture fraction fields is crucial for modeling combustion in fuel sprays. Therefore, a computational study has been performed to assess the effect of different parameters on the mixture formation and flow field in the simulation of a single jet of the engine combustion network (ECN) ''Spray G'' evaporative gasoline injection test case. The Lagrangian particle tracking (LPT) approach was tested within both Reynolds-averaged Navier-Stokes (RANS) and large eddy simulation (LES) frameworks, and the varieties were compared. Additional parameters that were considered include mesh resolution (0.75, 0.50, and 0.25 mm) and droplet breakup (Reitz-Diwakar, Reitz-KHRT, and Pilch-Erdman), as well as stochastic turbulent dispersion (O'Rourke) and stochastic collision (O'Rourke) models. Experimental penetration length data from both liquid and vapor phases were used to validate the 54 simulations performed within this study. Then, a series of analyses were performed to weigh the effect of each isolated parameter on the outcome of the simulations. Finally, three additional simulations were conducted to study specific issues of LES in fuel spray modeling. In this way, this study was able to make a qualitative comparison of the evaporative spray cloud shapes and the evaluation of spray statistics in terms of the iso-octane mixture fraction and droplet/slip velocities.
Assessment of LES-STRIP approach for modeling of droplet dispersion in diesel-like sprays
Oil & Gas Science and Technology – Revue d’IFP Energies nouvelles
In this paper, the stochastic equations of droplet motion in turbulent flow, proposed recently by Gorokhovski and Zamansky (2018, Phys. Rev. Fluids 3, 3, 034602), are assessed for turbulent spray dispersion in diesel like conditions along with Large Eddy Simulation (LES) for the gaseous flow. For droplets above the Kolmogorov length scale, this model introduces the concept of the stochastic drag, independently of laminar viscosity. For droplets below the Kolmogorov length scale, the model equation does depend on the laminar viscosity through the Stokes drag but the particle motion is stochastically forced. Both the stochastic drag and the stochastic forcing of the Stokes drag equation are based on the simple log-normal stochastic process for the viscous dissipation (ϵ) “seen” along the droplet trajectory. In this paper, this model is applied in the framework of two-way coupling, wherein the turbulence generated by the spray inturn controls the spray dispersion. The criterion for the...
Numerical Simulation of the Drop Size Distribution in a Spray
Springer Proceedings in Mathematics & Statistics, 2012
Classical methods of modeling predict a steady-state drop size distribution by using empirical or analytical approaches. In the present analysis, we use the maximum of entropy method as an analytical approach for producing the initial data; then we solve the coagulation equation to approximate the evolution of the drop size distribution. This is done by a quasi-Monte Carlo simulation of the conservation form of the equation. We compare the use of pseudo-random and quasi-random numbers in the simulation. It is shown that the proposed method is able to predict experimental phenomena observed during spray generation.
LES of atomizing spray with stochastic modeling of secondary breakup
International Journal of Multiphase Flow, 2003
A stochastic subgrid model for large-eddy simulation of atomizing spray is developed. Following KolmogorovÕs concept of viewing solid particle-breakup as a discrete random process, atomization of liquid blobs at high relative liquid-to-gas velocity is considered in the framework of uncorrelated breakup events, independent of the initial droplet size. KolmogorovÕs discrete model of breakup is rewritten in the form of differential Fokker-Planck equation for the PDF of droplet radii. Along with the Lagrangian tracking of spray dynamics, the size and number density of the newly produced droplets is governed by the evolution of this PDF in the space of droplet-radius. The parameters of the model are obtained dynamically by relating them to the local Weber number with two-way coupling between the gas and liquid phases. Computations of spray are performed for the representative conditions encountered in idealized diesel and gas-turbine engine configurations. A broad spectrum of droplet sizes is obtained at each location with coexistence of large and small droplets. A novel numerical algorithm capable of simultaneously simulating individual droplets as well as a group of droplets with similar properties commonly known as parcels is proposed and compared with standard parcels-approach usually employed in the computations of multiphase flows. The present approach is shown to be computationally efficient and captures the complex fragmentary process of liquid atomization.
Theoretical Investigation on Variable-Density Sprays
Atomization and Sprays, 2002
The aim of the present investigation is the analysis of the influence of liquid-fuel compressibility on the simulation of sprays produced by high-pressure injection systems. Two different equations have been introduced in the KIVA3V code to calculate liquid-phase density. The first one determines fuel density by using a second-order function of drop temperature and pressure, while the second one also takes into account the quantity of air dissolved in the fuel. Breakup, vaporization, and collision models as well as the energy, momentum, and air-spray mass exchange equations were modified so that each droplet would have a different density, according to its position and evolution. A comparison between experimental and numerical data for sprays injected in a constant-volume vessel at ambient temperature and pressure has been carried out to test the practical capability of the modified KIVA3V subroutines. The predicted and measured results of penetration versus time and drop size distribution showed good agreement. An in-depth study of the influence of gas temperature on the droplet vaporization rate has been performed for a single droplet and for sprays injected in a high-temperature, medium-pressure, constant-volume chamber. The effect of fuel density variability on vaporizing noncombusting sprays has been investigated for both models. The air dissolved in the fuel was found to affect liquid-phase density only at low ambient pressure. Finally, the experimental data measured on a small-bore diesel engine have been used to verify the provisional capabilities of constant-and variable-density models. NO and soot predictions have shown to be dependent on the model used for liquid-phase density.
Development and application of the drop number size moment modelling to spray combustion simulations
Applied Thermal Engineering, 2010
This work presents the development and implement of spray combustion modelling based on the spray size distribution moments. In this spray model, the droplet size distribution of spray is characterised by the first four moments related to number, radius, surface area and volume of droplets, respectively. The governing equations for gas phase and liquid phase employed here are solved by the finite volume method based on an Eulerian framework. These constructed equations and source terms are derived based on the moment-average quantities which are the key concept for this work. The sub-model employed for ignition and combustion is the coupling reaction rate between Arrhenius model and Eddy-Dissipation model (EDM) via a reaction progress variable. The results obtained from simulation are compared with the experimental and simulation data in the literature in order to assess the accuracy of present model. Comparing with the experimental results, present approach is capable to provide a qualitatively reasonable prediction for auto-ignition. In addition, the flame area developed during the combustion progress corresponds with the experimental data. However, the results of this model overpredict the measured flame temperature distributions. This might be due to the sub-model of turbulence/chemistry interaction employed here being based on infinitely fast chemistry assumption.
SAE Technical Paper Series, 2011
During the last fifteen years Computational Fluid Dynamics (CFD) has become one of the most important tools to both understand and improve the Diesel spray development in Internal Combustion Engine (ICE). Most of the approaches and models used pure Eulerian or Lagrangian descriptions to simulate the spray behavior. However, each one of them has both advantages and disadvantages in different regions of the spray, it can be the dense zone or the downstream dilute zone. One of the most promising techniques, which has been in development since ten years ago, is the Eulerian-Lagrangian Spray Atomization (ELSA) model. This is an integrated model for capturing the whole spray evolution, including primary break-up and secondary atomization. In this paper, the ELSA numerical modeling of Diesel sprays implementation in Star-CD (2010) is studied, and simulated in comparison with the Diesel spray which has been experimentally studied in our institute, CMT-Motores Térmicos. Since many of the most important characteristics of the spray development, as the penetration or the axial velocity, can be captured using 2D simulations, in this preliminary validation of ELSA model only two-dimensional simulations have been performed. Moreover, the main objective of the paper is to: firstly, obtain mesh independency for further analysis and secondly, improve the classic k-ε RANS model for ELSA model. Apart from this, several characteristics of the spray as can be the droplet formation of the liquid penetration are also showed.
SAE International Journal of Fuels and Lubricants, 2018
In order to improve understanding of the primary atomization process for diesel-like sprays, a collaborative experimental and computational study was focused on the near-nozzle spray structure for the Engine Combustion Network Spray D single-hole injector. These results were presented at the 5th Workshop of the Engine Combustion Network in Detroit, Michigan. Application of x-ray diagnostics to the Spray D standard cold condition enabled quantification of distributions of mass, phase interfacial area, and droplet size in the near-nozzle region from 0.1 to 14 mm from the nozzle exit. Using these data, several modeling frameworks, from Lagrangian-Eulerian to Eulerian-Eulerian and from Reynolds-Averaged Navier Stokes (RANS) to Direct Numerical Simulation (DNS), were assessed in their ability to capture and explain experimentally observed spray details. Due to its computational efficiency, the Lagrangian-Eulerian approach was able to provide spray predictions across a broad range of conditions. In general, this "engineering-level" simulation was able to reproduce the details of the droplet size distribution throughout the spray after calibration of the spray breakup model constants against the experimental data. Complementary to this approach, higher fidelity modeling techniques were able to provide detailed insight into the experimental trends. For example, interface-capturing multiphase simulations were able to capture the experimentally observed bi-modal behavior in the transverse interfacial area distributions in the near-nozzle region. Further analysis of the spray predictions suggests that peaks in the interfacial area distribution may coincide with regions of finely atomized droplets, whereas local minima may coincide with regions of continuous liquid structures. The results from this study highlight the potential of x-ray diagnostics to reveal salient details of the near-nozzle spray structure, and to guide improvements to existing primary atomization modeling approaches.