Modelling of sprays using a customized version of FLUENT

1. Modelling of sprays using a customized version of FLUENT Ahmed Elwardany (Brighton University, UK) Zhao Peng(Beijing Jiaotong University, China) The Sir Harry Ricardo Laboratories-Centre for Automotive Engineering 8th May 2012 Brighton –Research Workshop

2. Contents: • Introduction • Heat conduction equation • Species diffusion equation • Results • Concept of VOF • Conclusions and planned work

3. Introduction • Modelling of fuel droplets heating and evaporation process is important, where it affects the mixture preparation process and the ignition delay. • The most widely used assumption in CFD codes is that there is no temperature gradient inside the moving droplets. • Most of real fuels are multi-component fuels and each component has its own volatility. • Species diffusivity within multi-component droplet has been assumed to be infinitely large or small.

4. Introduction

5. Heat conduction equation • Heat conduction equation inside the droplet: • where is the liquid thermal diffusivity. • Boundary condition without evaporation:

6. Heat conduction equation • The solution to the heat conduction equation without evaporation for h = const is presented as follows: • are the solutions to the equation: • where

7. Heat conduction equation • The effect of droplet evaporation has been taken into account by replacing gas temperature by the so-called effective temperature. • The effect of circulation inside the droplet has been taken into account by replacing liquid thermal conductivity by effective liquid thermal conductivity

8. Species diffusion equation • Mass fraction equation inside the droplet: • Boundary condition: • where , ,

9. Species diffusion equation • The solution to the mass fraction equation for is presented as:

10. Species diffusion equation • is the solution to the equation: • (n>0) are the solutions to the equation:

11. Species diffusion equation • If the liquid mass fraction at droplet surface is known as the initial value • or the results of the solution to species diffusion equation, we can calculate: • where is the activity coefficient,

12. Species diffusion equation • For ideal mixture, . • For non-ideal mixture • (ethanol) • (acetone) • where

13. Results • Droplets stream • Fuel spray Proteus RCM, University of Brighton We used the dimension of the combustion chamber. Experimental results reproduced by: Maqua et al, (2008)

14. Results • Droplets stream • The first target is to implement the ETC/ED models into FLUENT successfully. • This is done by comparing the results of the in-house zero-dimensional code with the results of FLUENT with the UDF. • We assumed one-way solution for the validation process.

15. Results: Droplets stream Experimental results reproduced by: Maqua et al, (2008)

16. Results: Droplets stream

17. Results: Droplets stream Experimental results reproduced by: Maqua et al, (2008)

18. Results: Droplets stream

19. Results: Droplets stream

20. Results: Droplets stream

21. Results: Droplets stream

22. Results: Droplets stream

23. Preliminary results: Fuel spray

24. Volume of Fluid • VOF

25. Droplets Evaporation Using Volume of Fluid • 1.Introduction Droplets evaporation is of primary importance in internal combustion engines. The concentration of the fuel vapor is determined by the rate of evaporation of the droplets and it affects the performance of the combustion system. So we should pay much attention to droplet evaporation.

26. Recent research about droplets evaporation Many scholars have researched droplets evaporation using zero-dimension, one dimension and discrete particle method(DPM). But it can’t simulate droplet deformation using these methods. So I research the droplet evaporation using Volume of Fluid method(VOF), which can simulate the droplet deformation and temperature distrubution. Droplet Deformation

27. Volume of Fluid • 2.VOF method In computational fluid dynamics(CFD), the volume of fluid method (VOF method) is a numerical technique for tracking and locating the free surface. α is the volume fraction of liquid phase

28. The advantages of VOF method An advantage of VOF method is that as volumetric data is used to store interface location, conservation of volume is guaranteed (assuming incompressible fluids).  Another advantage of VOF method is that only one transport equation for the new variable (volume fraction) is used to describe the various changes of free surface. SLIC ( SIMPLE LINE INTERFACE CALCULATION） PLIC (Piecewise-Linear Interface Construction)

29. The Equations of VOF method VOF: Conservation of Mass : Conservation of Momentum: Conservation of Energy: Conservation of Mass Species:

30. Evaporation Rate: PLIC (Piecewise-Linear Interface Construction)

31. 3.Simulation Case and results Boundary condition: Computation region: Bottom region is mirror of the bottom

32. Grid independent

33. (1)Different Temperatures

34. (2)Different Pressures

35. (3)Oscillation flow

36. (3)Oscillation flow

37. (4)Experiment of Single Droplet in Different Temperatures Volume Fraction

38. (4)Experiment of Single Droplet in Different Temperature Heptane 550K

39. Conclusions • ETC is strongly recommended for implementation into CFD codes. • The predictions of the model of heating and evaporation of mono-component droplet have been validated against experimental data referring to measurements of average temperatures. • A simplified model for multi-component droplets heating and evaporation, applicable to finite number of components, has been developed and validated against the available experimental results and predictions of the vortex model. • This model has been successfully implemented into Fluent CFD code (one-way and coupled solution). • The simplified model for multi-component droplet heating and evaporation is generalised to take into the coupling between the droplets and the ambient gas.

40. Conclusions • VOF is a good method to research the droplet evaporation. • There are much differences of temperature distribution of droplets in different temperatures. • Droplet evaporation rate and fuel vapour mass fraction in droplet surface gradually decrease with environmental pressure increases. The droplet deformed strongly in higher environmental pressure.

41. Planned work • The concept of sphere of influence will be implemented into Fluent for the heating and evaporation process. • This model will be validated against engine-like conditions results. • A comparison between the predictions of the ETC model and VOF method will be considered. Both will be validated against experimental results for temperature distribution measurements.

42. Acknowledgements The authors are grateful to the European Regional Development Fund Franco-British INTERREGIVA (Project C5, Reference 4005) and EPSRC for financial support of the work on this project.

43. Publications: International Journals • Kristyadi T., Deprédurand V., Castanet G., Lemoine F., Sazhin S.S., Elwardany A., Sazhina E.M. and Heikal M.R. (2010), Monodisperse monocomponent fuel droplet heating and evaporation, Fuel 89 (2010) 3995–4001. • Sazhin S.S., Elwardany A.E., Krutitskii P.A., Castanet G., Lemoine F., Sazhina E.M. and Heikal M.R. (2010), A simplified model for bi-component droplet heating and evaporation, Int. J. Heat Mass Transfer 53, 4495–4505. • Abdelghaffar, W.A., Elwardany, A.E., Sazhin, S.S. (2011), Modelling of the processes in Diesel engine-like conditions: effects of fuel heating and evaporation, Atomization and Sprays, 53(13-14), 2826-2836. • Sazhin S.S., Elwardany A.E., Krutitskii P.A., Deprédurand V., Castanet G., Lemoine F., Sazhina E.M., Heikal M.R. (2011), Multi-component droplet heating and evaporation: numerical simulation versus experimental data, Int. J. Thermal Sciences, 50(2011) 1164-1180. • Sazhin S.S., Elwardany A.E., Sazhina E.M., Heikal M.R. (2011), A quasi-discrete model for heating and evaporation of complex multicomponent hydrocarbons fuel droplets, Int. J. Int. J. Heat Mass Transfer 54, 4325-4332. • Elwardany A.E. and Sazhin S.S. (2012), A quasi-discrete model for droplet heating and evaporation: Application to Diesel and gasoline fuels , Fuel [in press].

44. Thank you for your attentionYour questions are welcomed Ahmed Elwardany (Brighton University, UK) Zhao Peng(Beijing Jiaotong University, China) The Sir Harry Ricardo Laboratories-Centre for Automotive Engineering 8th May 2012 Brighton –Research Workshop