Modal decomposition of the unsteady flow field in compression-ignited combustion chambers

[EN] In this paper, the unsteady behaviour of a compression-ignited (CI) engine combustion chamber is studied by analysing the results of a Computational Fluid Dynamics (CFD) model through the application of different flow decomposition techniques, aiming to resolve the underlying modal structure of the process. Experimental validation for the combustion simulation is provided, and a methodology for extracting coherent pressure information is proposed in order to provide a suitable input for different analysis methods. These range from straightforward Fourier transform techniques to more sophisticated modal decomposition approaches. In particular Proper Orthogonal Decomposition (POD) is shown to provide valuable insight into the time-spatial structure of the combustion flow field, allowing the establishment of correlations between pressure modes and physical parameters of the combustion, such as the injection timing or the chamber geometry. Dynamic Mode Decomposition (DMD) on the other hand is proven to successfully highlight the link between the frequency of the unsteady energy components and their spatial distribution within the chamber. Advantage is then taken of the modal characterization of the unsteady behaviour in the chamber to showcase how physical parameters such as the spray angle can be modified to optimize the acoustic signature of the combustion process, helping CI internal combustion engines reduce their acoustic environmental impact (C) 2017 The Combustion Institute. Published by Elsevier Inc. All rights reserved.The equipment used in this work has been partially supported by FEDER project funds "Dotacidn de infraestructuras cientifico tecnicas para el Centro Integral de Mejora Energetica y Medioambiental de Sistemas de Transporte (CiMeT)" [grant number FEDER-ICTS-2012-06], framed in the operational program of unique scientific and technical infrastructure of the Spanish Government.Torregrosa, AJ.; Broatch, A.; Garcia Tiscar, J.; Gómez-Soriano, J. (2018). Modal decomposition of the unsteady flow field in compression-ignited combustion chambers. Combustion and Flame. 188:469-482. https://doi.org/10.1016/j.combustflame.2017.10.007S46948218

An experimental and modeling study of the shock tube ignition of a mixture of n-heptane and n-propylbenzene as a surrogate for a large alkyl benzene

Journal articleAlkyl aromatics are an important chemical class in gasoline, jet and diesel fuels. In the present work, an n-propylbenzene and n-heptane mixture is studied as a possible surrogate for large alkyl benzenes contained in diesel fuels. To evaluate it as a surrogate, ignition delay times have been measured in a heated high pressure shock tube (HPST) for a mixture of 57% n-propylbenzene/43% n-heptane in air (approximate to 21% O-2, approximate to 79% N-2) at equivalence ratios of 0.29, 0.49, 0.98 and 1.95 and compressed pressures of 1, 10 and 30 atm over a temperature range of 1000-1600 K. The effects of reflected-shock pressure and equivalence ratio on ignition delay time were determined and common trends highlighted. A combined n-propylbenzene and n-heptane reaction mechanism was assembled and simulations of the shock tube experiments were carried out. The simulation results showed very good agreement with the experimental data for ignition delay times. Sensitivity and reaction pathway analyses have been performed to reveal the important reactions responsible for fuel oxidation under the shock tube conditions studied. It was found that at 1000 K, the main consumption pathways for n-propylbenzene are abstraction reactions on the alkyl chain, with particular selectivity to the allylic site. In comparison at 1500 K, the unimolecular decomposition of the fuel is the main consumption pathway. (C) 2012 The Combustion Institute. Published by Elsevier Inc. All rights reserved.Saudi Aramc