Development of an efficient solver for detailed kinetics in reactive flows
Doctoral thesis, 2021
In the first phase of the PhD work, an isomer lumping strategy based on thermodynamic data was developed and applied to a detailed three component reaction mechanism for n-decane, alpha-methylnaphthalene and methyl decanoate comprising 807 species and 7807 reactions. A total of 74 isomer groups were identified within the oxidation of n-decane and methyl decanoate via the assessment of the Gibbs free energy of the isomers. The lumping procedure led to a mechanism of 463 species and 7600 reactions, which was compared against the detailed version over several reactor conditions and over a broad range of temperature, pressure and equivalence ratio. In all cases, excellent agreement between the predictions obtained using the lumped and the detailed mechanism has been observed with an overall absolute error below 12%.
In the second phase of the PhD work, a tabulated chemistry approach was developed, implemented and validated against an on-the-fly chemistry solver across different simulation frameworks. As a first attempt, a flamelet-based tabulation method for soot source terms was coupled to the stochastic reactor model and tested against a well stirred reactor-based approach under Diesel engine conditions. The main purpose was to assess and quantify benefits of tabulation within the 0-D SRM framework with respect to soot formation only. Subsequently, a latent enthalpy (h298) based approach was developed and implemented within the SRM model to predict both combustion and emission formation. This approach was widely validated against the detailed on-the-fly solver solutions under 0-D reactor conditions as well as Diesel engine conditions for a wide range of operating points. Good agreement was found between the two solvers and a remarkable speed-up was obtained in terms of computational costs of the simulation. As a last step, the same tabulated chemistry solver was coupled to a commercial CFD software via user defined functions and performances were assessed against the built-in on-the fly chemistry solver under Diesel engine sector simulations. The tabulated chemistry solver proved to be within an acceptable level of accuracy for engineering studies and showed a consistent speed-up in comparison to the online chemistry solver.
Across all the investigated frameworks, the developed tabulated chemistry solver was found to be a valid solution to speed-up simulation time without compromising accuracy of the solution for combustion and emissions predictions for engine applications. In fact, the much-reduced CPU times allowed the SRM to be included in broader engine development campaigns where multi-objective optimization methods where efficiently used to explore new engine designs.
Stochastic Reactor Model
Chalmers, Mechanics and Maritime Sciences, Combustion and Propulsion Systems
Matrisciano A., Seidel L., Mauss F., "An a priori Thermodynamic Data Analysis based Chemical Lumping Method for the Reduction of Large and Multi-component Chemical Kinetic Mechanisms" Submitted to International Journal of Chemical Kinetics
Soot Source Term Tabulation Strategy for Diesel Engine Simulations with SRM
SAE Technical Papers,; Vol. 2015(2015)
Paper in proceeding
Development of a Computationally Efficient Progress Variable Approach for a Direct Injection Stochastic Reactor Model
SAE Technical Papers,; (2017)
Paper in proceeding
A Computationally Efficient Progress Variable Approach for In-Cylinder Combustion and Emissions Simulations
SAE Technical Papers,; Vol. 2019-September(2019)
Paper in proceeding
Development of a Computationally Efficient Tabulated Chemistry Solver for Internal Combustion Engine Optimization Using Stochastic Reactor Models
Applied Sciences,; Vol. 10(2020)p. 1-31
The automotive sector, and especially internal combustion engine R&D engineers have strongly benefited from advanced reactive flow models and have managed to develop cleaner and more efficient powertrain systems. However, given the high complexity of the system to model (i.e., turbulence, multi-phase flows, complex pollutant formation mechanisms) the formulation of reliable and yet computationally efficient reactive flow models still represents a very challenging task.
The present thesis aims to formulate, implement and validate a generally applicable set of methods to 1) automatically reduce the size of the chemical system that governs the simulation of the combustion process; 2) pre-compile a comprehensive thermo-chemical database and use it as a look-up table during the computation of complex reactive flow systems such as internal combustion engines. The main objective of both methods is essentially to reduce the computational time required to run the engineering simulation without compromising too much the accuracy of the solution.
Both methods developed in the present work delivered remarkable speed-ups with respect to currently existing models, while keeping the solution accuracy within acceptable error ranges. Robustness and computational performance of the models were also tested under multi-objective optimization and large design of experiment campaigns with satisfactory results. In general, the proposed methods proved to be attractive solutions that could make the digital powertrain development cycle faster, while keeping the benefits and detail of high order combustion chemistry models.
Fuel Flexible Engine Platform (FLEX II)
Swedish Energy Agency (39368-2,2018-008000), 2018-10-01 -- 2020-09-30.
Fluid Mechanics and Acoustics
Areas of Advance
Information and Communication Technology
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4943
Chalmers University of Technology
Zoom (Meeting passcode: 471892) | Blixtlåset, SB3, Sven Hultins gata 8, Room 2042.
Opponent: Professor Christian Hasse, Technical University of Darmstadt