Computational Combustion Laboratory (CCL)



Computational Combustion Modeling | Combustion-generated Pollutants | Atmospheric Soot | High-performance Computing



Characaterizing multiphysics interaction in combustion devices

Combustion involves complex interactions of fluid dynamics, multiphase flows, chemical reactions, and heat transfer. Our understanding of combustion is still incomplete because of the complexity of each of these processes and their interactions. Effect of these interactions could become very important for practical combustion devices such as engines, particularly while trying to estimate or understand pollutant emissions. Without a comprehensive understanding, it is not possible to come up with a comprehensive strategy for mitigation of combustion-generated pollutants. This research project takes a detailed look into varius aspects of effects of interactions between turbulence, chemistry, and thermal radiation at different scales of combustion with specific interest in formation of soot and NOx.

Soot and turbulence
Fig: Layers of soot (colored by volume fraction) in a turbulent planar flame.


Aging of soot at the exhaust of combustion systems

In the context of global climate change, combustion-generated soot or black carbon is a major concern [1,2]. Unfortunately our understanding of evolution of soot in atmosphere is very limited. Freshly-formed soot undergoes a dramatic change in its physical and chemical properties as it mixes with other aerosols and volatile matters in the exhaust of the combustion devices and in atmosphere. This research project aims to understand the physics of these changes in soot so that we can be better equipped to predict its effect in atmosphere.

[1] U.S. EPA., EPA/600/R-08/139F. 2009.
[2] Bond, T. C. et al, J. Geophys. Res. Atmos., 118:1-173. 2013


Towards efficient and scalable radiation solvers in combustion

Radiation is one of the most important mode of heat transfer in any combustion system [1,2]. Accurate modeling of radiative transfer, however, is very complex and computationally very intensive, even for relatively simple configurations. Difficulties of resolving radiation in combustion system stems from two direction: (a) highly nonlinear radiative properties of participating media, and (b) high dimensionality of the radiative transfer equation (RTE). While there are several approximate models for both the hurdles (such as WSGG, FSK, etc. for radiative properties and DOM, PN, DTM, etc for RTE solver), one line-by-line photon Monte Carlo (LBL/PMC) can produce accurate results while resolving both the problems of nonlinear radiative properties and high dimensioanlity. The disadvantage of LBL/PMC is its computational cost both in terms of time and memory requirements. This project aims to improve the current state-of-the-art of LBL/PMC scheme to increase its scalability so that it can be employed in massively parallel computations without loosing accuracy.

[1] Modest, M. Radiative Heat Transfer, 3rd Ed. Academic Press, NY, U.S. 2013.
[2] Modest, M and Haworth, D. Radiative Heat Transfer in Turbulent Combustion Systems: Theory and Applications. 1st Ed. Springer. 2016.

Memory use
Fig: Improvement in shared memory use in LBL/PMC using new scheme.

Scaling
Fig: Strong scaling efficiency of different schemes in PMC without any load balancing.


Radiation modeling in multiphase combustion

Many real-world combustion system involve multiphase combustion, e.g., spray combustion in internal combustion engines, coal combustion in furnaces, etc. Impact of radiation in multiphase combustion is poorly captured by current thermal radiation models [1-3]. Presence of a discrete phase makes multiphase radiation modeling even more difficult than radiation modeling of participating gases. The radiative properties of sprays and coal particles are also not very well studied. The radiative interaction between droplets and particles not only depend on the radiative properties of the fuel, but also their size distribution. This research project aims to develop detailed and efficient radiation models for multiphase combustion.

[1] Modest, M. Radiative Heat Transfer, 3rd Ed. Academic Press, NY, U.S. 2013.
[2] Sazhin, S. Droplets and Sprays, 1st Ed. Springer. 2014.
[3] Erfurth, J. Radiative Heat Transfer in Coal-Fired Furnaces and Oxycoal Retrofit Considerations, 1st Ed. Shaker Verlag, 2012.

Coal radiation
Fig: Ratio of convective to radiative heat transfer in a coal flame. Blue means convection dominated, red means radiation dominated.

Spray radiation
Fig: Impact of multiphase radiation in a high-pressure spray combustion.


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