Determination of heat flows inside turbochargers by means of a one dimensional lumped model

In the present paper, a methodology to calculate the heat fluxes inside a turbocharger from diesel passenger car is presented. The heat transfer phenomenon is solved by using a one dimensional lumped model that takes into account both the heat fluxes between the different turbocharger elements, as well as the heat fluxes between the working fluids and the turbocharger elements. This heat transfer study is supported by the high temperature differences between the working fluids passing through a typical diesel turbocharger. These flows are the hot exhaust gases coming from the diesel engine exhaust passing through the turbine, the fresh air taken by the compressor, and the lubrication oil passing through the housing. The model has been updated to be used with a new generation of passenger car turbochargers using an extra element in the heat transfer phenomenon that is the water cooling circuit. This procedure allows separating the aerodynamic from the heat transfer effects, permitting to study the behavior of compressor and turbine in a separated way. (C) 2011 Elsevier Ltd. All rights reserved.Olmeda González, PC.; Dolz Ruiz, V.; Arnau Martínez, FJ.; Reyes Belmonte, MA. (2013). Determination of heat flows inside turbochargers by means of a one dimensional lumped model. Mathematical and Computer Modelling. 57(7-8):1847-1852. doi:10.1016/j.mcm.2011.11.078S18471852577-

Application of the two-step Lax and Wendroff FCT and the CE-SE method to flow transport in wall-flow monoliths

[EN] Gas dynamic codes are computational tools applied to the analysis of air management in internal combustion engines. The governing equations in one-dimensional elements are approached assuming compressible unsteady non-homentropic flow and are commonly solved applying finite difference numerical methods. These techniques can also be applied to the calculation of flow transport in complex systems such as wallflow monoliths. These elements are characterized by alternatively plugged channels with porous walls. It filters the particulates when the flowgoes through thewall from the inlet to the outlet channels. Therefore, this process couples the solution of every pair of inlet and outlet channels. In this study, the adaptation of the two-step Lax and Wendroff method and the space-time Conservation Element and Solution Element method is performed to be applied in the solution of flow transport in wall-flow monolith channels. The influence on the prediction ability is analysed by a shock-tube test and experimental data obtained under impulsive flow conditions.This work has been partially supported by the Spanish Ministerio de Ciencia e Innovacion through grant number DPI2010-20891-C02-02.Serrano, JR.; Arnau Martínez, FJ.; Piqueras, P.; García Afonso, Ó. (2014). Application of the two-step Lax and Wendroff FCT and the CE-SE method to flow transport in wall-flow monoliths. International Journal of Computer Mathematics. 91(1):71-84. https://doi.org/10.1080/00207160.2013.783206S718491

Molecular-orbital theory for the stopping power of atoms in the low velocity regime:the case of helium in alkali metals

A free-parameter linear-combination-of-atomic-orbitals approach is presented for analyzing the stopping power of slow ions moving in a metal. The method is applied to the case of He moving in alkali metals. Mean stopping powers for He present a good agreement with local-density-approximation calculations. Our results show important variations in the stopping power of channeled atoms with respect to their mean values.Comment: LATEX, 3 PostScript Figures attached. Total size 0.54

Derivation of the method of characteristics for the fluid dynamic solution of flow advection along porous wall channels

This paper describes in detail a novel formulation of the method of characteristics for its application to solve one-dimensional compressible unsteady non-homentropic flow advected along porous wall channels. In particular, the method is implemented into a wall-flow monolith Diesel particulate filter model whose purpose is the pressure drop prediction. The flow inside the monolith channels is considered to be one-dimensional and the flow through the porous wall treated as a source term agree with the Darcy's law. The flow dynamic behaviour at internal nodes of the channels is solved by means of shock capturing methods, whereas the end nodes, or boundary conditions, are solved applying the method of characteristics. The derived solution in this study of the Riemann variables and the entropy level includes the variation along the space-time plane due to cross-section area changes, friction and heat transfer as traditionally stated, but also takes into account the key influence on every line of the flow leaving or entering to the channels through the porous walls. © 2011 Elsevier Inc.Desantes Fernández, JM.; Serrano Cruz, JR.; Arnau Martínez, FJ.; Piqueras Cabrera, P. (2012). Derivation of the method of characteristics for the fluid dynamic solution of flow advection along porous wall channels. Applied Mathematical Modelling. 36:3134-3152. doi:10.1016/j.apm.2011.09.090S313431523

On the effect of different flux limiters on the performance of an engine gas exchange gas-dynamic model

[EN] A suitable tool for the design of intake and exhaust systems of internal combustion engines is provided by time domain non-linear finite volume models. These models, however, are affected by overshoots at discontinuities and numerical dispersion unless some flux limiter is used. In this paper, the effect of the most relevant of such flux limiters on a non-linear staggered-mesh finite-volume model is evaluated. Flux-Corrected-Transport (FCT) and Total Variation Diminishing (TVD) schemes, together with a Momentum Diffusion Term (MDT) are presented for such a model, and the performance of the resulting methods is checked in different problems representative of the influence of engine gas exchange flows on engine performance and intake and exhaust noise. First, two one-dimensional cases are considered: the shock-tube problem, and the propagation of a finite amplitude pressure pulse. Secondly, a simple but representative three-dimensional geometry is studied. From the results obtained, it can be concluded that, even if none of the methods is able to handle properly the three problems considered, the FCT method provides the best overall performance. (C) 2017 Elsevier Ltd. All rights reserved.M. Hernandez is partially supported through contract FPI-S2-2015-1064 of Programa de Apoyo para la Investigacion y Desarrollo (PAID) of Universitat Politecnica de Valencia.Torregrosa, AJ.; Broatch, A.; Arnau Martínez, FJ.; Hernández-Marco, M. (2017). On the effect of different flux limiters on the performance of an engine gas exchange gas-dynamic model. International Journal of Mechanical Sciences. 133:740-751. https://doi.org/10.1016/j.ijmecsci.2017.09.029S74075113

Assessment of a methodology to mesh the spatial domain in the proximity of the boundary conditions for one-dimensional gas dynamic calculation

[EN] Solution of governing equations for one-dimensional compressible unsteady flow has been performed traditionally using a homogenously distributed spatial mesh. In the resulting node structure, the internal nodes are solved by applying a shock capturing finite difference numerical method whereas the solution of the end nodes, which define the boundary conditions of the pipe, is undertaken by means of the Method of Characteristics. Besides the independent solution of every method, the coupling between the information obtained by the method of characteristics and the finite difference method is key in order to reach a good accuracy in gas dynamics modeling. The classical spatial mesh could provide numerical problems leading the boundary to generate lack of mass, momentum and energy conservation because of the interpolation methodology usually applied to draw the characteristics and path lines from its departure point at calculation time to the end of the pipe during the next time-step. To deal with this undesirable behavior, in this work a modification of the traditional grid including an extra node close to the boundary is proposed in order to explore its ability to provide numerical results with higher conservation fulfillment. © 2010 Elsevier Ltd.J.R. Serrano; Arnau Martínez, FJ.; Piqueras, P.; Reyes Belmonte, MA. (2011). Assessment of a methodology to mesh the spatial domain in the proximity of the boundary conditions for one-dimensional gas dynamic calculation. Mathematical and Computer Modelling. 54:1747-1752. doi:10.1016/j.mcm.2010.11.073174717525

A fluid dynamic model for unsteady compressible flow in wall-flow diesel particulate filters

The use of particulate filters (DPF) in Diesel engines has become in recent years the standard technology for the control of soot aerosol emissions. Once emissions reduction through the management of filtration and regeneration aspects has reached its maturity, the effect of the system location on engine performance and acoustics are key topics to be addressed. In this paper, a fluid dynamic model for wall-flow monolith filters is described in which non-homentropic one-dimensional unsteady compressible flow is considered. The good agreement with experimental data confirms that the model is able to describe the mechanisms contributing to the pressure drop across the whole filter under steady and impulsive flow conditions. The approach of the flow governing equations provides a reliable evaluation of the contributions to the pressure drop with axial resolution in the description of the flow field properties. In addition, the frequency response predicted by the model confirms its ability to evaluate the dynamic response and acoustic potential of the DPF. © 2010 Elsevier Ltd.This work has been partially supported by the Spanish Ministerio de Ciencia e Innovacion through grant number DPI2010-20891-C02-02.Torregrosa Huguet, AJ.; Serrano Cruz, JR.; Arnau Martínez, FJ.; Piqueras Cabrera, P. (2011). A fluid dynamic model for unsteady compressible flow in wall-flow diesel particulate filters. Energy. 36(1):671-684. https://doi.org/10.1016/j.energy.2010.09.047S67168436