Eulerian-Lagrangian spray modelling and computational fluid dynamics simulation

and validation frameworkby

Dr. Charalambos A. ChasosAssistant Professor

Frederick University, Cyprus

Smart Energy Carriers: Modelling, Data and Data Analysis-Biblioteca “Ferdinando Gasparini”

April 5, 18:10- 18:30

First Workshop of the Working Group 4 of the SMARTCATs COST Action CM1404University Frederico II of Naples, Italy – April 5-6, 2016

CONTENTS• Introduction

– Objectives– Approach

• Eulerian-Lagrangian spray modelling methodology– Sensitivity studies– Validation practices

• Background research work– Diesel spray simulation and validation– GDI injector simulations and validation– GDI spray simulations and validation

• Discussion on validation data– Single and multiple-pulse spray prediction– Experimental data of spray droplets

• Current and future work• References

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INTRODUCTION: -Objectives

• Outline the Eulerian-Lagrangian spray modelling methodology sensitivity analyses

• Describe the practices used for Eulerian-Lagrangian spray simulation and validation investigations

• Present spray simulations and validation investigations and emphasize on the requirement for validation data

• Analyze raw experimental spray data

• Present and discuss single and multiple-pulse spray predictions

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INTRODUCTION: -Approach

• Present validation studies of constant volume chamber sprays including Diesel spray and gasoline direct injection (GDI) spray simulations and comparisons against experiments

• Present raw experimental spray data and analyse spray droplet data measurements including droplet size and velocity, placing emphasis on data scatter, ensemble-average data and standard deviation

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Eulerian-Lagrangian modelling framework:

• Governmental equations of the gas phase (Eulerian approach) and liquid phase (Lagrangianapproach)

• Turbulence modelling of the gas phase (k-ε high Reynolds number and variants)

• Atomisation modelling (special for injector type) for the initial droplet size and velocity distributions

• Spray sub-models for droplet breakup and collision, and droplet dispersion model

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SPRAY MODELLING: -Methodology

Sensitivity studies of the key numerical parameters:

• Mesh size Δx (use Courant number criterion Co = u Δt / l, where l is the cell diagonal length)

• Time step size Δt (use Courant number criterion)

• Parcel introduction rate (defines the total mass of liquid injected in the time interval (t, t + Δt) distributed over a certain number of parcels Np)

=> Identify the solution independence on the above three parameters

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SPRAY MODELLING: -Sensitivity analyses

• The overall simulation methodology is expected to be validated against extensive experimental data from constant-volume chambers and optical engines

• It is difficult to perform engine in-cylinder spray measurements, so these are often carried out in constant-volume chambers, where better optical access can be provided and ambient conditions can be readily adjusted

• However, the majority of the studies are experimental and/or computational, with relatively few validation studies

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SPRAY MODELLING: -Validation practices

Validation of sprays considers:

• Qualitative data of spray visualisation for comparisons of spray structure and shape

• Quantitative data in the form of ensemble-average quantities evaluated from multiple spray pulses (due to limitation of the sampling rate), including:– Spray tip penetration

– Droplet size

– Droplet velocity measurements

– Fuel vapor field

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SPRAY MODELLING: -Validation practices

Diesel injector and spray simulations (from Chasoset al. 2012)• Motivation: In direct-injection Diesel ICE the quality of the air-fuel

mixture is highly affected by the characteristics of the injector and the pattern of the spray jet emerging from the injector nozzle. The phenomena take place in small scales and are very complex.

• Methodology: CFD modelling and simulation of the internal injector flow and spray development in fine computational meshes. – The Eulerian single-phase modelling methodology was used for

the simulation of the fuel flow in a multi-hole Diesel injector.– The Eulerian/Lagrangian two-phase flow modelling

methodology was employed for simulations of the sprays produced at atmospheric and at high pressure and temperature conditions. Validation of the results against published experiments

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BACKGROUND RESEARCH: -Diesel spray

• Results: Section view at the symmetry plane of the velocity and pressure fields in the injector

The higher velocities of the field are displaced towards the upper edge of the nozzle, and cavitation takes place at the nozzle inlet area, which is expected to affect the jet emerging from nozzle and spray atomisation.

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BACKGROUND RESEARCH: -Diesel spray

• Validation: Qualitative comparison of the predicted spray droplet parcels against spray photograph for chamber pressure 42 bar and temperature 1000 K, at 1.5 ms ASOI

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Spray penetration is slightly overpredicted and is in good agreement with the experiment. The estimation of the experimental spray tip and shape is qualitative.

BACKGROUND RESEARCH: -Diesel spray

Simulation Experiment

• Validation: Comparison of spray tip penetration for Diesel (B0) and biodiesel (B100) fuels at high pressure and temperature conditions

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BACKGROUND RESEARCH: -Diesel spray

Gasoline direct-injection (GDI) injector simulations (from Chasos 2014)• Motivation: In DISI engines, the quality of the air-

fuel mixture is highly affected by the injection and ambient conditions, including fuel type and injection pressure.

• Methodology: CFD modelling and simulation of the internal injector flow and the liquid sheet development. – The Eulerian modelling methodology along with the

volume of fluid method were used for the two-phase flow simulation of the emerging gasoline liquid sheet at increasing injection pressures.

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BACKGROUND RESEARCH: -GDI injector

Validation: Qualitative comparisons of simulations with spray photographs at 0.8 ms ASOI (different scales)

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3m

m

BACKGROUND RESEARCH: -GDI injector

• Validation: Comparison of the spray cone angle from the simulations against the measured angle from the spray photographs for 50, 80 and 100 bar injection pressure, at 0.8 ms ASOI.

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BACKGROUND RESEARCH: -GDI injector

• Findings: – The film thickness at the nozzle exit slightly

increased with increasing injection pressure. – The effect of the injection pressure on the spray

angle was negligible, while the liquid sheet breakup length decreases with increasing injection pressure.

– From the simulations and comparisons against the measured spray angles, it was found that the spray angle was slightly overpredicted.

– The simulation provides the initial spray angle and droplet velocities for Eulerian/Lagrangian spray modelling and simulation

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BACKGROUND RESEARCH: -GDI injector

Gasoline direct-injection (GDI) injector simulations (from Chasos 2006)

• Motivation: In DISI engines, the spray injection and the preparation of the combustible air/fuel mixture is crucial for the design of efficient GDI engines.

• Methodology: Spray atomisation model development and CFD modelling and simulation of the overall engine spray injection simulation was performed – Three spray atomisation models were developed and the

Eulerian/Lagrangian spray modelling was validated against extensive qualitative and quantitative experimental data in constant volume chambers and a motored DISI engine

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BACKGROUND RESEARCH: -GDI sprays

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BACKGROUND RESEARCH: -GDI spraysValidation: Constant volume chamber spray predictions comparison with spray photographs at 0.8, 1.2 and 1.5 msASOI for injection pressure 70 bar

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BACKGROUND RESEARCH: -GDI spraysValidation: Spray penetration predictions comparison with measurements for injection pressure 70 bar

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BACKGROUND RESEARCH: -GDI sprays

Validation: Motored engine in-cylinder spray predictions comparison with spray photographs

Single and multiple-pulse spray predictions for the main body of the spray at 70 bar injection pressure (variation of random initial droplet size for 30 different pulses)

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DISCUSSION ON VALIDATION DATA

• Raw data from multiple-pulse PDA measurement of droplet size at location (25, 13). Large population that scatters

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DISCUSSION ON VALIDATION DATA

Spray location

r = 11 mm, z = 25 mm ->

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DISCUSSION ON VALIDATION DATA

Experimental data Simulation data

• The experiment is of course the reality, where randomness exists, for example in the injector operation, the atomisation process, and the flow field interactions due in part to the turbulence

• The spray which is produced from each injection pulse is thus different

• In spray simulations of the kind which are considered in the present study the ensemble-averaged Navier-Stokes equations are used to model the gas phase and the Lagrangian approach is employed for the liquid

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DISCUSSION ON VALIDATION DATA

• The Lagrangian spray equations are not ensemble-averaged while the gas equations are ensemble-averaged

• Thus, one spray pulse is in principle not sufficient to describe the stochastic spray behaviour and therefore number of spray realisations are required

• It is therefore clear that care is required when comparing single-pulse simulation results with experimental data

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DISCUSSION ON VALIDATION DATA

• Examine and quantify the randomness incurred in different types of sprays

• Identify the range where the single-pulse simulation data is valid from multiple-pulse simulations and comparisons with various sets of experiments for different injectors and for wide range of conditions

• Carry out validation of the air/fuel and combustion simulations in constant volume chambers for Diesel and GDI sprays

• Carry out full engine modelling and simulation of Diesel engine using spray initial conditions determined from full injector modelling and simulation (using detailed injector geometry and injection history)

• Carry out Diesel and GDI engine simulation validations, especially quantitative comparisons, for various operating conditions

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CURRENT AND FUTURE WORK

1. Chasos, C. A. "CFD simulation of the emerging liquid sheet from a high-pressure swirl injector at increasing injection pressures". Proceedings of ILASS 2014, 26th European Conference on Liquid Atomization & Spray Systems. Bremen, Germany, 8-10 September 2014. (Paper ref. No. 128).

2. Chasos, C. A., Christodoulou, C. N. and Karagiorgis, G. N. “CFD simulations of multi-hole Diesel injector nozzle flow and sprays for various biodiesel blends”. Proceedings of ICLASS 2012, 12th Triennial International Conference on Liquid Atomization and Spray Systems, Heidelberg, Germany, September 2-6, 2012. (Paper ref. No. 1263).

3. Chasos, C. A. “Computational fluid dynamics simulation of direct injection gasoline sprays”. PhD thesis, Imperial College of Science Technology and Medicine, University of London, England, 2006.

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REFERENCES

Thank you for your attention