Pedro Piqueras

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

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

Assessment by means of gas dynamic modelling of a pre-turbo diesel particulate filter configuration in a turbocharged HSDI diesel engine under full-load transient operation

Diesel particulate filters (DPF) are becoming a standard technology in diesel engines because of the need for compliance with forthcoming regulations regarding soot emissions. When a great degree of maturity in management of filtration and regeneration has been attained, the influence of the DPF placement on the engine performance emerges as a key issue to be properly addressed. The novelty of this work leads to the study of an unusual location of an aftertreatment device in the architecture of the turbocharged diesel engine exhaust line. The problem of the pre-turbo DPF placement is tackled comparing the engine response under full-load transient operation as opposed to the traditional DPF location downstream of the turbine. The study has been performed on the basis of a gas dynamic simulation of the engine, which has been validated with experimental data obtained under steady-state and transient conditions. The DPF response has been simulated with a model able to deal with the characteristic highly pulsating flow upstream of the turbine. Several levels of DPF soot loading have been considered to represent fully the most exigent conditions in terms of performance requirements. As a result, the main physical phenomena controlling the engine and DPF response and interaction have been identified. Placing the DPF upstream of the turbine will lead to a number of important advantages, owing to the continuous regeneration mode at which the DPF will operate, the lower pressure drop in the DPF, and the thermal energy storage in the DPF, which is very useful to mitigate ‘turbocharger lag’ during engine transient operation. These three effects have been evidenced with calculations performed using the validated model and the results have been fully analysed and discussed.

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.

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.

Analysis of heavy-duty turbocharged diesel engine response under cold transient operation with a pre-turbo aftertreatment exhaust manifold configuration

Diesel particulate filters are the most useful technology to reduce particulate matter from the exhaust gas of internal combustion engines. Although these devices have suffered an intense development in terms of the management of filtration and regeneration, the effect of the system location on the engine performance is still a key issue that needs to be properly addressed. The present work is focused on a computational study regarding the effects of a pre-turbo aftertreatment placement under full and partial load transient operation at constant engine speed and low wall temperature along the exhaust line. The aim of the paper is to provide a comprehensive understanding of the engine response to define the guidelines of a control strategy that is able to get the standards of engine driveability during sudden accelerations under restraining thermal transient conditions governed by the aftertreatment thermal inertia. The proposed strategy overcomes the lack of temperature at the inlet of the turbine caused by the thermal transient by means of the boost and EGR control. It leads to a proper management of the power in the exhaust gas for the expansion in the turbine.

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.

Representation Limits of Mean Value Engine Models

Mean Value Engine Models (MVEMs) have been widely used for internal combustion engine modelling with main application areas on the design and development of engine control systems. However, modellers must be aware of the limitations of these MVEMs which are associated to the simplification of the geometry and the time scale, and the partial consideration of the physical phenomena involved. This chapter analyses through several real-life examples the effects of some of the most important simplifications done in MVEMs.

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

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 wall-flow monoliths. These elements are characterized by alternatively plugged channels with porous walls. It filters the particulates when the flow goes through the wall 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.

Analysis of shock capturing methods for chemical species transport in unsteady compressible flow

Abstract This paper presents a chemical species transport model to account for variable composition and gas properties along the flow path in internal combustion engines. The numerical solution to adapt the gas dynamic model to chemical species transport in boundary conditions by means of the Method of Characteristics and in volumes by means of a filling and emptying model is described. The performance for chemical species transport in 1D elements of shock-capturing methods, such as the two-step Lax–Wendroff method and the Sweby’s TVD scheme considering several flux limiter definitions, is carried out by means of shock-tube tests. The influence of the fluid modelling as perfect or non-perfect gas on the numerical methods features and the flow characteristics on shock-tube results are analysed.