F. J. Arnau

Description of a Semi-Independent Time Discretization Methodology for a One-Dimensional Gas Dynamics Model

Modeling has become an essential technique in design and opti- mization processes of internal combustion engines. As a conse- quence, the development of accurate modeling tools is, in this moment, an important research topic. In this paper, a gas- dynamics modeling tool is presented. The model is able to repro- duce the global behavior of complete engines. This paper empha- sizes an innovative feature: the independent time discretization of ducts. It is well known that 1D models solve the flow through the duct by means of finite difference methods in which a stability requirement limits the time step depending on the mesh size. Thus, the use of small ducts in some parts of the engine reduces the speed of the calculation. The model presented solves this limita- tion due to the independent calculation for each element. The different elements of the engine are calculated following their own stability criterion and a global manager of the model intercon- nects them. This new structure provides time saving of up to 50% depending on the engine configuration. DOI: 10.1115/1.2983015

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

Abstract 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.

Description and Analysis of a One-Dimensional Gas-Dynamic Model With Independent Time Discretization

Modeling has become an essential technique in design and optimization processes of internal combustion engines. As a consequence, the development of accurate modeling tools is, in this moment, an important research topic. In this paper, a gas-dynamics modeling tool is presented. The model is able to reproduce the global behavior of complete engines. Besides, it is able to calculate different components of the engine individually like the turbocharger, the intercooler, the catalyst, the cylinders or the diesel particulate filter. Finally, the paper emphasizes an innovative feature: the independent time discretization of ducts. It is well known that 1-D models solve the flow through the duct by means of finite difference methods in which a stability requirement limits the time step depending on the mesh size. Thus, the use of small ducts in some parts of the engine reduces the speed of the calculation. The model presented solves this limitation due to the independent calculation for each element. The different elements of the engine are calculate following their own stability criterion and a global manager of the model interconnects them. This new structure provides time saving of up to 50% depending on the engine configuration.Copyright

Importance of Heat Transfer Phenomena in Small Turbochargers for Passenger Car Applications

This paper is partially supported by the Universitat Politecnica de Valencia PAID-06-11 2034.

A semi-implicit space-time CE-SE method to improve mass conservation through tapered ducts in internal combustion engines

In this work, we present a semi-implicit method based on the CE-SE numerical scheme (space time conservation-element and solution-element). In particular, we apply this method to a hyperbolic system that models the dynamics of an unsteady flow along a tapered duct with friction and heat transfer. Conditions on the scheme in order to get real numerical solutions are given. The improvement that offers the semi-implicit method versus the scheme CE-SE is compared by means of numerical simulations based on the property of the mass conservation.

Solution of the turbocompressor boundary condition for one-dimensional gas-dynamic codes

Nowadays, turbocharged engines are widely used in cars and trucks. Gas-dynamic codes are an important tool in design and optimization of these types of engines. These codes solve the one-dimensional governing equations in ducts for compressible, unsteady and non-homoentropic flow. The ducts are generally solved using finite difference schemes, the volumes are solved by means of filling and emptying models and the connections represent the boundary conditions of the ducts. One important boundary condition is the compressor which connects two ducts. In this junction an increment of momentum and energy is undergone by the flow but depending on its sense the behaviour is different. This paper presents the mathematical base of a compressor model which solves this complex boundary condition. The governing equations of the model have been presented in detail. The solution involves a non-linear equation system that has to be solved iteratively. The Newton-Raphson root-finding method has been chosen to get its solution. Finally, some results of the model have been compared to measurements focusing in surge prediction.

On-engine measurement of turbocharger surge limit

In this article a new experimental technique is presented to measure the turbocharger surge limit in a regular engine test bench. It is known that the surge margin on engine tests may be very different from that obtained in a steady-flow gas-stand. In particular, surge is very dependent on the flow pattern produced by the compressor inlet duct and also on the piping upstream and downstream the compressor. The proposed technique that is based on the injection of pressurized air into the intake manifold is compared with the other ways of measuring the compressor map on engine. Some results with different compressor arrangements are presented and discussed. It is demonstrated that this technique allows for measuring not only the actual surge line but also the complete compressor performance map.

1D gas dynamic modelling of mass conservation in engine duct systems with thermal contact discontinuities

A detailed analysis of mass non-conservation in the proximity of thermal contact discontinuities, when solving 1-D gas dynamic flow equations with finite difference numerical methods, is carried out in this paper. A wide spectrum of finite difference numerical methods has been applied to solve such conditions. Thermal contact discontinuities are very common in current diesel engines due to back-flow in the intake valves during the valve overlap period. Every method has been shown to be incapable of correctly solving the problem raised, displaying (or revealing) a different behavior. Taking as base line these analyses a study regarding mesh size reduction in ducts has been also performed. This solution becomes suitable since it leads to making mass conservation problems disappear. Nevertheless, most extended calculation structure in 1D gas dynamic models is not advised due to the increase of computational effort required. Thus, a new calculation structure for solving governing equations in ducts is suggested. This proposed calculation structure is based on independent time discretisation of every duct according to its CFL stability criterion. Its application to thermal contact discontinuities points out its advantages with regard to computational demand as the calculation time of every duct is adapted to its mesh size.

High-frequency response of a calculation methodology for gas dynamics based on Independent Time Discretisation

A calculation methodology to solve the one-dimensional governing equations system is presented. This calculation methodology is based on the Independent Time Discretisation (ITD) of the ducts composing the system. The purpose is the improvement of the trade-off between the accuracy and the computational cost that the current 1D gas dynamic models can yield. The ITD methodology is applied to the specific problem of noise prediction in internal combustion engines in order to evaluate its performance in the frequency domain. The application of the ITD methodology to the well-known acoustic configurations which are representative of the main attenuation mechanisms in commercial mufflers shows its ability. The potential is evaluated in terms of reduction of the computational cost and the accuracy and robustness provided by the results as a function of the spatial mesh size and the family of finite difference numerical method applied.

General Procedure for the Determination of Heat Transfer Properties in Small Automotive Turbochargers

The work has been partially supported by Ministerio de Economia y Competitividad, Secretaria de Estado de Investigacion. Subdireccion de proyectos de investigacion (TRA2013-40853-R).