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Technical Paper

Study of the Influence of the Injection System in a Multi-Dimensional Spray Simulation

The introduction of the high-pressure fully electronic-controlled injection systems has opened a number of new possibilities to optimize diesel engine performance and to reduce pollutant emissions. However greater research efforts are required to meet future European emission legislation. The control of the combustion process, which determines to a large extent the amount of pollutant emissions, requires primarily an understanding of its physics and chemistry as well as the capability to modify one or more of the interdependent process parameters in a given direction. Since many parameters have to be considered, a combined experimental-numerical approach is required.
Technical Paper

Study of the Impact on the Spray Shape Stability and the Combustion Process of Supply Pressure Fluctuations in CR-Diesel Injectors

The paper presents a study of the influence of fuel pressure supply fluctuations on the upstream side of the fuel injector atomizer. The study is performed over a wide range of pressures (70 to 130 Mpa) with two different common-rail (CR) high-pressure fuel injectors. The common atomizer is a VCO-type equipped with conically shaped atomizer bores. With the injector tip (nozzle) mounted in a counter-pressure vessel the pressure fluctuations in the fuel-rail and in the injector body are recorded simultaneously with stroboscopic Schlieren-visualization of the time-resolved spray behavior. It is demonstrated that not only the instantaneous mass flow is affected. As a function of rail-pressure, pulse-width and injection strategy the pressure fluctuations change the spray hard-core structure and its break-up behavior.
Technical Paper

Study of the Impact on the Combustion Process of Injector Nozzle Layout creating Enhanced Secondary Spray Break-up

The paper presents a study of a key-element in the mixture preparation process. A typical common-rail (CR) high-pressure fuel injector was fitted with a prototype injector nozzle with atomizer bores of a particular conical layout. It is demonstrated within certain layout limits, that a considerable enhancement can be obtained for the secondary break-up of the hard-core fluid sprays produced by the nozzle. The impact on the combustion process is examined in terms of pressure and heat release as well as of the engine-out pollutant emission. The results are compared to those of an earlier developed CR high-pressure injector nozzle. The atomization behavior of the prototype nozzle is illustrated through experimental results in terms of engine-out emissions from a 1.3-liter turbo-charged passenger car diesel engine. The detailed spray behavior is visualized on a component test rig by use of specially developed optical visualization techniques.
Technical Paper

Combustion and Spray Simulation of a DI Turbocharged Diesel Engine

The recent innovations on automotive Diesel engines require significant research efforts. The new generation of fully electronically controlled injection systems have opened new ways to reduce emissions and improve the efficiency of the engine. The free mapping of injection law together with the enhanced injection pressures favor, in fact, the optimization of mixture formation. In this field, the 3D simulation is playing a substantial role to support the design of combustion chamber. This paper presents a computational model to simulate the multi-injection process, the mixture formation and the combustion of DI diesel engines with high-pressure injection systems. The main code is a modified version of the KIVA 3V and the modifications presented in this work are a high pressure break up model and a multi component evaporation model. The code has been validated through experimental data on a 4-cylinder, 1910 cc, DI turbocharged Diesel engine (Fiat 1.9 JTD).
Technical Paper

Experimental Validation of a GDI Spray Model

A computational model and an experimental analysis have been performed to study the atomisation processes of hollow cone fuel sprays from a high pressure swirl injector for gasoline direct injection (GDI) engines. The objective has been to obtain reliable simulations and better understood structure and evolution of the spray and its interaction with air the flow field. The 3D computations are based on the KIVA 3 code in which basic spray sub models have been modified to simulate break-up phenomena and evaporation process. Spray characteristics have been measured using a system, able to gather and to process spray images, including a CCD camera, a frame grabber and a pulsed sheet obtained by the second harmonic of Nd-YAG laser (wavelength 532 nm, width 12 ns, thickness 80 μm). The readout system has been triggered by a TTL signal synchronized with the start of injection. A digital image processing software has been used to analyse the collected pictures.
Technical Paper

Atomization of High-Pressure Diesel Spray: Experimental Validation of a New Breakup Model

A hybrid model for the atomization of Diesel sprays was developed [1]. The model was added to the KIVA code to better simulate spray evolution. Different implementation for low-medium and high injection pressure sprays are performed. It has already been validated for the low-pressure case [1,2] and in this work it was tested for high injection pressure systems, in a vessel at ambient conditions. It distinguishes between jet primary breakup and droplet secondary breakup. For the latter distinct models are used, as the droplet Weber number changes in the various regimes, in order to take into account the effects of the different relevant forces. For high pressure Diesel spray the effects of jet turbulence, cavitation and nozzle flow on liquid core primary breakup must be considered. Due to the high droplet velocity the catastrophic secondary breakup regime may occur.
Technical Paper

Enhanced Mixture Preparation Approach for Lean Stratified SI-Combustion by a Combined Use of GDI and Electronically Controlled Valve-Timing

The first part of the paper gives an overview of the current status in fuel consumption gain of the GDI-vehicles previously launched on the European market. In order to increase the potential for a further gain in specific fuel consumption the behaviour of 3 different combustion chamber layouts are studied. The chamber layouts are aimed to adapt as well as possible to the particular requirements for application to a small displacement/small bore engine working in stratified lean conditions. The paper continues with a description of the application that shows the different steps of a structured optimisation methodology for a 1.2 litre, small bore 4-cylinder engine. The applications of an air-motion-guided and a wall-guided layout with a mechanically actuated valve train to the same combustion chamber are discussed. The potential of the air-motion-guided concept is enhanced through the introduction of an electromagnetic fully variable valve train.
Technical Paper

Experimental and Numerical Approach to Injection and Ignition Optimization of Lean GDI-Combustion Behavior

The first part of the paper gives an overview of the current development status of the GDI system layout for the middle displacement engine, typically 2 liter, using the stoichiometric or weak lean concept. Hereafter are discussed the particular requirements for the transition to a small displacement/small bore engine working in stratified lean conditions. The paper continues with a description of the application of the different steps of the optimization methodology for a 1.2 liter, small bore 4 cylinder engine from its original base line MPI version towards the lean stratified operation mode. The latest changes in the combustion model, used in the numerical simulation software applied to the combustion chamber design, are discussed and comparison made with the previous model. The redesign of the combustion chamber geometry, the proper choice of injector atomizer type and location and the use of two-stage injection and multi-spark strategies are discussed in detail.
Technical Paper

Mass Transfer Improvements in Catalytic Converter Channels: An Hybrid BGK-Finite Volume Numerical Simulation Method

For compliance with future LEV/ULEV emission standards in United States and Euro 2000/Euro 2005 standards in European Community, catalytic converter performance has to be remarkably improved. The development of simulation codes allows to investigate a high range of possible exhaust system configurations and engine operating parameters. In the present study an hybrid Lattice BGK-finite volume technique will be described, able to determine the mass transfer rates of the chemical species to the catalyzed wall of the monolith channels. The BGK code solves the fluid motion governing equations in a reduced form obtained by discretizing the continuum in a fixed number of particles. Each of them will be moved by a set of discrete velocities and collide with the neighbour particles according to a fixed pattern of particle-interaction.
Technical Paper

A Simulation Model for a High Pressure Injection Systems

Pollutant emissions from D.I. Diesel engines strongly depend on injection system characteristics and mainly on injection pressure and timing. In the latest years some solutions have been proposed based on very high fuel pressure values (up to 150 MPa). Among them, the so called “Common rail” system configuration, being able to electronically control needle lift and injection pressure, seems to be particularly promising. Much experimental and theoretical work has been done to improve system performance for automotive applications. With the aim of investigating the influence of some details of geometrical configuration on the injector operating mode, a mathematical model able to describe the pressure-time history in any section of the delivery pipe and the fuel injection rate through the nozzle has been developed, based on a semi-implicit finite volumes approach. The computed results have been compared with experimental data provided by the Institut Français du Pétrole.