Marco Antonelli

Influence of Mixture Formation on Injection and Combustion Characteristics in a Compact GDI Engine

The spray characteristics are determining factors for the quality of mixture formation respectively for the combustion, when applying GDI. Their variation with load and speed is a basic criterion for the adaptability of an injection system type to an engine with known requirements. CFD models of the fluid flow dynamics, mixture formation and combustion are a determining condition for such adaptation. The paper presents the development results of a GDI four-stroke, four-valve, single cylinder engine. The pressure pulse injection system involved in this application is analyzed and presented from the fluid-dynamic behavior up to the obtained injection spray characteristics. The mixture formation and combustion processes are simulated for different load and speed values, respectively for favorable combinations of parameters, such as the injection system configuration, the opening pressure of the applied mechanical injector and the injection duration. Particular aspects of the combustion when using GDI, such as non-homogeneity of the mixture structure, super position of mixture formation and combustion and the influence of additional spark sources form an object of analysis. The results of numerical simulation are compared with the experimental results. Complete paper available under: http://www.sae.org/servlets/productDetail?PROD_TYP= PAPER&PROD_CD=2002-01-0997

Lumped Parameters Modeling of an Incinerator With Heat Recovery for Energy Production

This work shows the modeling of an incineration plant with energy recovery which operates in the vicinity of Pisa, Italy. The plant analysed was built formerly as an incineration plant and was recently refurbished with a heat recovery steam generator to drive a condensing steam turbine. In the foresight of an enlargement of the plant capacity, the Technical Office of the Company asked the Energetica Department of University of Pisa for an analysis of the recovery capability. The Technical Office and the Energetica Department decided to create a lumped parameter model in order to simulate the temperature behavior of the combustion products. This model was created inside Matlab/Simulink environment. The followed procedure led to the reproduction of the system interested by the cycle in steady state conditions in order to obtain a model simple enough but at the same time rigorous of the real behavior of steam cicle. After the description of the plant modeling, model calibration and validation is shown, by means of the comparison between the measured and simulated values of temperatures and mass flows in several load conditions. The model developed is currently used by the Technical Office of the Company for further developments of the plant.Copyright

A Cooling System Effectiveness Prediction Methodology through the use of Analytical and Numerical Techniques

ABSTRACT The use of numerical techniques is widely accepted bymanufactures in order to increase engine durability andperformances and reduce emissions. The effective thermalload prediction is always considered a nodal point tocorrectly assess the coolant mass flow rate and jacketsarrangement.In literature many approaches used to analyzed the in-cylinder heat transfer can be found and they can be classifiedas follows: methods based on the steady convective heattransfer, approaches based on the solution of the unsteadyheat conduction equation by means of the knowledge of thetemperature profile, approaches based on the energyconservation for the whole mass contained inside thecylinder.The purpose of this paper is to define a proper methodologyto evaluate the thermal flow distribution and intensity insidethe engine liner, head and coolant channel. In facts, this workshows the analysis of the cooling circuit of a small single-cylinder, four-stroke, high power density engine carried outwith a numerical, three-dimensional CFD analysis using acommercial CFD 3D code.A numerical conjugate analysis is presented in this work anda particular attention was used to define realistic boundaryconditions. Furthermore, a sensitivity study on mesh was alsocarried out.This study is based on the knowledge of the mean steady heatflow and takes into consideration the following topics:• the evaluation of the needed coolant mass flow by means ofan analysis based on the Woschni approach;• the analysis of the velocity and temperature field by meansof a conjugate heat transfer simulation of the whole head andcylinder group.This work includes the comparison of the numerical resultswith data collected by literature and experiments.

A NUMERICAL PROCEDURE FOR THE EVALUATION OF THE ENGINE HEAD-CYLINDER GROUP COOLING EFFECTIVENESS

The purpose of this paper is to investigate the thermal flows and heat transfer phenomena occurring in the cooling circuit of a high specific power engine and to suggest a valid method to evaluate its effectiveness in keeping the temperature below a safety limit even in the highest thermal power points. This is a first work showing the analysis of the cooling circuit of a small single-cylinder, four-stroke, high power density gasoline engine carried out with a numerical three-dimensional CFD analysis by means of a CFD conjugate simulation, whose boundary conditions have been taken from a validated one-dimensional fluid dynamic engine model. Once its validity has been assessed by the comparison between the simulation results and data collected by literature and experiments, the interest for this procedure relies on the fact that heat fluxes are directly calculated by the CFD code through the knowledge of gas temperatures and convective heat transfer coefficients. Hence an arbitrary, a priori subdivision of the total heat flux released by fuel combustion into heat converted into mechanical work, heat released to the cooling system, heat rejected to the exhaust, etc. can be avoided; at the same time, the model provides the proper distribution of the heat rejected to the various surfaces constituting the water jackets. The evaluation of the effectiveness of the cooling system is then directly performed in terms of temperature distribution. By this way, once the engine has been designed from a fluid dynamic and mechanical point of view, the effectiveness of the cooling system can be immediately verified through the application of the described procedure. This study takes into consideration the evaluation of average and instantaneous heat transfer coefficient and in-cylinder gas temperature through the use of a validated 1D CFD model, the analysis of the temperature field by means of a conjugate heat transfer simulation of the whole head and cylinder group and an example of the application of this procedure for the evaluation of a simple modification of the cooling system.Copyright

1d modelling and simulation of a piezo injector for spray guided gasoline direct injection systems

The aim of this work was the modelling and the simulation of the Piezo injector, developed by Siemens VDO Automotive for “spray guided” Gasoline Direct Injection (GDI) systems. The development of the model was based on a 1D lumped parameter approach, which was performed in the AMESim environment. The injector was accurately modelled in its three subsystems, namely the piezo actuator, the thermal compensator and the valve body, in order to have a complete control on its behaviour. The reliability and the accuracy of the models of each subsystem were evaluated through comparisons with experiments for various operating points. The last part of this work describes some applications where the model was used and it demonstrates how accurate modelling and simulation may allow a real contribution in the understanding and optimization of the injector behaviour, reducing time and costs that are involved in an only experimental analysis.Copyright

Optimization of an internal combustion engine for an hybrid scooter

A very stringent problem in most of European cities is the individual mobility. This problem is mainly caused by traffic jam and arising from this are two particularly interesting environmental issues: pollution and noise [1]. Use of two wheeler vehicles does not represent the final solution to these problems, nevertheless they can supply a useful aid to ease them. Recently, two stroke engines are being replaced with four stroke engines. For small capacity engines this means a true reduction in exhaust emissions, especially unburned hydrocarbons (HC), but, on the other hand it involves a performance reduction, particularly for sudden accelerations, which constitute an essential requirement for these vehicles [2, 3, 4, 5]. Hybridisation can help to fill the gap between two stroke engines and cleaner, but less performing four stroke engines [6]. At the same time, it can help to lower fuel consumption, by means of a reduction in the revolution speed [2, 5]. This paper presents a study on a parallel hybrid scooter prototype from the point of view of a better matching between the characteristics of the internal four stroke combustion engine and of the electric motor. Wave fluiddynamic 1D code was used in order to create a model of the internal combustion engine. The model validation was carried out by the comparison between the simulation results and the experimental data obtained with the roller test bench. Then, some modifications were analysed in order to optimise the behaviour of the engine at a lower revolution speed of the engine, thus diminishing the specific fuel consumption of the vehicle. Finally, such modifications were introduced in a Simulink (Matlab) model to evaluate their influence on the behaviour of the whole hybrid vehicle when running on different road cycle tests.