Abstract
Abstract Soot prediction for diesel engines is a very important aspect of internal combustion engine emissions research, especially nowadays with very strict emission norms. Computational Fluid Dynamics (CFD) is often used in this research and optimisation of CFD models in terms of a trade-off between accuracy and computational efficiency is essential. This is especially true in the industrial environment where good predictivity is necessary for engine optimisation, but computational power is limited. To investigate soot emissions for Diesel engines, in this work CFD is coupled with chemistry tabulation framework and semi-empirical soot model. The Flamelet Generated Manifold (FGM) combustion model precomputes chemistry using detailed calculations of the 0D homogeneous reactor and then stores the species mass fractions in the table, based on six look-up variables: pressure, temperature, mixture fraction, mixture fraction variance, progress variable and progress variable variance. Data is then retrieved during online CFD simulation, enabling fast execution times while keeping the accuracy of the direct chemistry calculation. In this work, the theory behind the model is discussed as well as implementation in commercial CFD code. Also, soot modelling in the framework of tabulated chemistry is investigated: mathematical model and implementation of the kinetic soot model on the tabulation side is described, and 0D simulation results are used for verification. Then, the model is validated using real-life engine geometry under different operating conditions, where better agreement with experimental measurements is achieved, compared to the standard implementation of the kinetic soot model on the CFD side.
Highlights
Diesel combustion is still very important in the modernday world, as it is being used in many fields, from transportation to energy production and heavy-duty applications
Due to strict emission regulations, it is necessary to optimise it in terms of produced NOx and soot particles, which is often on the opposite sides of the spectrum: emission-reduction techniques tend to increase soot emission while reducing NOx emission, and vice versa [1]
Since it is necessary to model both combustion and soot emissions, two approaches are discussed here: Flamelet Generated Manifold (FGM) implemented in the tabulation framework, and kinetic soot model implemented in both Computational Fluid Dynamics (CFD) and tabulation
Summary
Diesel combustion is still very important in the modernday world, as it is being used in many fields, from transportation to energy production and heavy-duty applications. Empirical models are the simplest ones, presented by equations that are adjusted to match experimental soot profiles [6] Since they do not predict a time evolution of soot particles, but rather just a final value at exhaust for the engine, these models are of very limited use in CFD calculations and are used mainly for testing purposes. Pang et al showed a six-step phenomenological soot model with particle dynamics and PAH chemistry integrated into the model [7] It covers particle inception, surface growth, coagulation and surface oxidation, as well as soot precursor formation and oxidation. Surface growth, coagulation and surface oxidation, as well as soot precursor formation and oxidation It is an extensive model, but its usage is prohibited in industrial environments due to high computational complexity. A look-up procedure is used to retrieve this value during the online CFD simulation
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
