J.R. Serrano

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.

Modelling of turbocharged diesel engines in transient operation. Part 1: Insight into the relevant physical phenomena

Abstract A new calculation model, able to predict the engine performance during an engine transient, has been developed, based on an existing wave action code. Previously to the model development, the turbocharged diesel engines transient phenomena (turbocharger lag, thermal transient and energy transport delay) were deeply analysed on the basis of experimental information. The study has been focused on the load transient, i.e. torque increase from idle, at constant engine speed of a high speed direct injection (DI) turbocharged engine. Experimental load transient tests have been performed, with the aim of obtaining a combustion database during engine transient operation, to input into a combustion simulation submodel. The applied methodology allows the characterization of the transient combustion process in any DI turbocharged engine.

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

An experimental procedure to determine heat transfer properties of turbochargers

Heat transfer phenomena in turbochargers have been a subject of investigation due to their importance for the correct determination of compressor real work when modelling. The commonly stated condition of adiabaticity for turbochargers during normal operation of an engine has been revaluated because important deviations from adiabatic behaviour have been stated in many studies in this issue especially when the turbocharger is running at low rotational speeds/loads. The deviations mentioned do not permit us to assess properly the turbine and compressor efficiencies since the pure aerodynamic effects cannot be separated from the non-desired heat transfer due to the presence of both phenomena during turbocharger operation. The correction of the aforesaid facts is necessary to properly feed engine models with reliable information and in this way increase the quality of the results in any modelling process. The present work proposes a thermal characterization methodology successfully applied in a turbocharger for a passenger car which is based on the physics of the turbocharger. Its application helps to understand the thermal behaviour of the turbocharger, and the results obtained constitute vital information for future modelling efforts which involve the use of the information obtained from the proposed methodology. The conductance values obtained from the proposed methodology have been applied to correct a procedure for measuring the mechanical efficiency of the tested turbocharger.

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.

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 Mechanical Losses Modeling in the Performance Prediction of Radial Turbochargers under Pulsating Flow Conditions

This work presents a study to characterize and quantify the mechanical losses in small automotive turbocharging systems. An experimental methodology to obtain the losses in the power transmission between the turbine and the compressor is presented. The experimental methodology is used during a measurement campaign of three different automotive turbochargers for petrol and diesel engines with displacements ranging from 1.2 l to 2.0 l and the results are presented. With this experimental data, a fast computational model is fitted and used to predict the behaviour of mechanical losses during stationary and pulsating flow conditions, showing good agreement with the experimental results. During pulsating flow conditions, the delay between compressor and turbine makes the mechanical efficiency to fluctuate. These fluctuations are shown to be critical in order to predict the turbocharger behaviour.

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.

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.

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.