Towards Accurate and Validated Open-Source Simulations

of Rapid Compression Machines for The Study of Novel Fuels Séan J. Gorry 1,2,3,4, Karl Alexander Heufer 5, Henry J. Curran 2,3,4, Francesco Contino 6, Nathan J. Quinlan 1,2,3, Rory F.D. Monaghan 1,2,3,4

1 School of Engineering, National University of Ireland Galway 2 Ryan Institute for Environmental, Marine and Energy Research, Galway 3 MaREI@NUIG 4 Combustion Chemistry Centre, National University of Ireland Galway 5 Physico-Chemical Fundamentals of Combustion, RWTH Aachen University 6 BURN Joint Research Group, Vrije Universiteit Brussel, Université Libre de Bruxelles

Motivation

Understanding the combustion chemistry of fuels is a vital aspect in the development of new,

highly efficient ICEs (Internal Combustion Engines) and gas turbines. This knowledge of the

combustion chemistry is used to reduce emissions, and to ensure that detrimental phenomena,

such as knocking, do not occur. RCMs (Rapid Compression Machines) are used to study the

auto-ignition behavior of fuel mixtures, and the results that are produced are used to develop

chemical kinetic mechanisms. These chemical kinetic mechanisms are widely used to model

combustion and reacting flows.

Fig 1. ICE Damage Caused by Knocking [1] Fig 2. Rapid Compression Machine [2]

OpenFOAM Methodology

As the cylinder volume decreases during the compression stroke, a dynamic mesh is required.

To this end, two separate approaches are being examined.

1. Topology Change with Layer Removal

This approach uses a custom mesh solver, linearMotionLayersFvMesh, which uses the

OpenFOAM mesh modifier layerAdditionRemoval. This means that cells are removed during the

compression.

Fig 7. Layer Removal

2. Solution Mapping

The second approach uses solution mapping. The fluid domain is separated into several regions,

each of which is solved individually. After one region has been solved, the results are ‘mapped’ to

the next region.

Fig 8. Solution Mapping Problems with RCMs

An issue that arises during the operation

of an RCM, is that of temperature

inhomogeneity. As the piston moves

through the cylinder, rollup vortices are

formed. These vortices result in the

transportation of cool gas from the

cylinder walls into the core of the gas

mixture. The use of a piston crevice

mitigates against the formation of these

vortices.

Fig 3. Vortex Formation [3] Fig 4. Temperature Inhomogeneity [4]

OpenFOAM Open-Source CFD

OpenFOAM is a CFD toolbox that has an extensive library

of solvers for both static and dynamic analyses. It is

widely used in academia in lieu of expensive commercial

software. The potential for its use in the study of RCMs

was highlighted by Bourgeois et al., (2018) (Fig 6.) Its

use also facilitates a combined modelling approach

within the RCM community.

Fig 6. OpenFOAM® LES RCM Simulation [6]

Numerical Modelling

Due to the important role crevice design has in the

operation of RCMs, its design is critical. A great deal of

numerical analysis has been conducted into crevice

design. Of particular note is the work of Yousefian, et

al., (2018) (Fig 5.). This work found that a 3D LES (Large

Eddy Simulation) simulation was required when

undertaking advanced analysis into crevice design.

Fig 5. LES Simulation of RCM 100 ms after EOC [5]

Current Progress

To date, the majority of work has been on the development of the changing topology approach.

This method has a distinct advantage in that cell deformation is reduced. Figure 9 shows mesh

deformation for cases with

1. No topological change or solution mapping

2. Solution mapping with three regions

3. Topological change with layer removal

Fig 9. Mesh Deformation (t=1 @ EOC)

Future Work

• Further development of linearMotionLayersFvMesh solver

• Development of solution mapping case for full compression stroke

• Evaluation of layer addition removal and solution mapping methods

• Transition from RANS turbulence models to LES

Acknowledgments

I would like to thank the School of Engineering NUI Galway, the Combustion Chemistry Centre

NUI Galway, and PCFC RWTH Aachen University for the funding that they have provided.

References [1] Wang, Zhi & Liu, Hui & Reitz, Rolf. (2017). Knocking combustion in spark-ignition engines. Progress in Energy and Combustion Sci-

ence. 61. 78-112. 10.1016/j.pecs.2017.03.004.

[2] Chung, J. et al. (2015) ‘Rapid-compression machine studies on two-stage ignition characteristics of hydrocarbon autoignition and an investigation of new gasoline surrogates’, Energy. Pergamon, 93, pp. 1505–1514. doi: 10.1016/J.ENERGY.2015.09.077.

[3] ALLEN, J. J. and CHONG, M. S. (2000) “Vortex formation in front of a piston moving through a cylinder,” Journal of Fluid Mechanics. Cambridge University Press, 416, pp. 1–28. doi: 10.1017/S002211200000865X.

[4] Würmel, J. and Simmie, J. M. (2005) ‘CFD studies of a twin-piston rapid compression machine’, Combustion and Flame, 141(4), pp. 417–430. doi: https://doi.org/10.1016/j.combustflame.2005.01.015.

[5] Yousefian, Sajjad & Quinlan, Nathan & Monaghan, Rory. (2018). Simulation of turbulent flow in a rapid compression machine: Large Eddy Simulation and computationally efficient alternatives for the design of ignition delay time experiments. Fuel. 234. 10.1016/j.fuel.2018.06.117.

[6] Bourgeois, N. et al. (2018) ‘How to ensure the interpretability of experimental data in Rapid Compression Machines? A method to validate piston crevice designs’, Combustion and Flame. Elsevier, 198, pp. 393–411. doi: 10.1016/J.COMBUSTFLAME.2018.09.030.

Objectives

• Development of 3D LES OpenFOAM case for single piston RCM

• Flow visualisation using Reynolds equivalent apparatus

• Development of 3D LES OpenFOAM case for double piston RCM

• Visualisation using PIV (Particle Image Velocimetry) and MTV (Molecular Tagging Velocimetry)