J. Galindo

Modelling of turbocharged diesel engines in transient operation. Part 2: Wave action models for calculating the transient operation in a high speed direct injection engine

Abstract Part 1 of this paper analysed the physical phenomena involved in the transient operation of turbocharged diesel engines, together with the principles of diesel combustion characterization during the transient process. This second part describes a calculation model developed to predict engine transient performance based on an existing wave action code. Relevant improvements introduced are combustion process simulation and modelling of heat transfer, variable geometry turbine behaviour and mechanical losses. Experimental load transient tests with a high speed direct injection engine have been performed, with the aim of assessing the model accuracy. The main evaluation parameters were instantaneous variation during turbocharger rotating speed transient, boost pressure, air mass flow, injected fuel and exhaust pressures.

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

A methodology to identify the intake charge cylinder-to-cylinder distribution in turbocharged direct injection Diesel engines

Exhaust gas recirculation (EGR) is currently the most important NOx emission control system. During the last few years the EGR rate has increased progressively as pollutant emission regulations have become more restrictive. High EGR rate levels have given the effect of the unsuitable EGR and air distribution between cylinders away, which causes undesirable engine behavior. In this sense, the study of the EGR distribution between cylinders achieves high importance. However, despite the fact that the EGR is continuously under study, not many studies have been undertaken to approach its distribution between cylinders. In concordance with the aspects outlined before, the aim of this paper is to propose a methodology that permits us to identify the EGR cylinder-to-cylinder dispersion in a commercial engine. In order to achieve this objective, experimental tests have been combined with both one-dimensional and three-dimensional fluid dynamic models.

Analysis and Modeling of the Fluid-Dynamic Effects in Branched Exhaust Junctions of ICE

The influence of exhaust junction geometry on flow-dynamics of exhaust gas is analyzed. The authors propose an experimental characterization method based on the measurement of the instantaneous pressure in the junction operating with engine exhaust flow and solving the problems posed for the accurate instantaneous pressure measurements under the adverse temperature condition. In this paper, the method is applied to two Y type junctions, with a reed being the unique difference between them, to determine the influence of this element on the junction behavior. The analysis of the experimental results denotes two major differences: the characteristics of the wave reflected at the junction, and the energy of the pulse transmitted to the lateral branch of the junction. The results of the analysis are introduced in the junction modeling used in a one-dimensional gas dynamic model with an important improvement in the agreement of the modeled predictions with the experimental measurements.

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 of a sequentially turbocharged diesel engine on real-life driving cycles

The article presents the development of the control manager of a parallel sequential turbocharger system. This control manager must decide the transition between the different operation modes of the boosting system. The control manager must protect the system from surge and over-speed risks.The methodology followed in the development process was based on the use of concurrence survey data from a similar engine, the simulation with a 1D code and finally the assessment on engine test bench. Real-life driving cycles were used during the development process, which were acquired in three different driving scenarios (city, road and mountain road).

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.

Coupling methodology of 1D finite difference and 3D finite volume CFD codes based on the Method of Characteristics

This paper describes the methodology followed to perform a co-simulation between 1D (OpenWAM) and 3D (FLUENT) CFD codes. The Method of Characteristics (MoC) has been chosen to transfer the information between the two domains by properly updating the boundary condition at the shared interface. A short explanation of the MoC is provided, including the modifications needed by the Riemann invariants when dealing with non-homentropic flow. The implementation of the coupling is explained, focusing on the particular approach required by FLUENT in order to obtain the Riemann invariants. Two validation tests have been performed. The Sods problem has been used to test the numerical accuracy of the coupling methodology. On the other hand, an impulse test rig configuration has been simulated to show the potential capability of a co-simulation in terms of reducing the computational cost. In both cases a good agreement in the solution is found.

Simulations and measurements of automotive turbocharger compressor whoosh noise

Turbocharger noise has become a major concern in downsized automotive engine development. In this paper, the analysis is focused on the whoosh noise produced by the compressor when it is working near surge. A centrifugal compressor has been acoustically characterized on a turbocharger test rig mounted on an anechoic chamber. Three in-duct pressure signals forming a linear array are registered in order to obtain pressure components. In this way, meaningful pressure spectra and sound intensity level (SIL) compressor maps are obtained, showing an increase of SIL in the frequency window corresponding to whoosh noise. Besides, detached eddy simulations (DES) of the centrifugal compressor flow in two operating conditions near surge are performed. Good agreement is found between the experimental measurements and the CFD solutions in terms of predicted pressure spectra. Flow analysis is used to identify patterns responsible for the different features of the pressure spectra. At the simulated conditions, rotating instabilities in the compressor diffuser and inducer cause pressure oscillations in the frequency range of whoosh noise.