Luigi Martorano

Hydrogen injection in two-stroke reciprocating gas engines

Abstract A research study in the field of hydrogen-fed engines aims to obtain sufficient maximum power and to avoid any combustion anomaly which might prevent the engine from operating in normal conditions. Thus to investigate the direct injection of hydrogen into the cylinder, with the aim of better combustion with subsequent higher specific outputs, would seem, in the present state of the art, very interesting. During research directed at finding the optimum performance of the engine, three parameters were changed, namely: the quantity of injected hydrogen, total injection timing and timing of ignition before top dead center. This experimental set-up was performed for several injection nozzles using a two-stroke Piaggio engine of 200 cc.

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

Numerical Optimization of a Gasoline Direct Injection Concept Adapted for High Speed Two-Stroke Engines

The future development of two-stroke engines will be conditioned by the drastic reduction of pollutant emission, especially of hydrocarbon. This goal is not achievable only by scavenging improvement, rather a new quality of mixture formation using direct injection is imposed. However, the internal mixture formation in a large range of speed and load, considering the scavenge flow particularities of two-stroke engines as well, appears as an extremely complex process. Thereby a numerical simulation is in this case very effective for the adaptation of a direct injection method at the engine. The paper presents a concept for modeling and optimization of the mixture formation process within a high-speed two-stroke engine with liquid fuel injection system. The injection system generates a pressure pulse which is not dependent on the engine speed. The paper illustrates the mixture formation process as time and space related, in base on the fuel volume distribution and mixture velocity within the combustion chamber. The numerical simulation of the mixture formation is based on the commercial code FLUENT. The time dependent simulations covered both the injection duration and the subsequent mixing process, in order to evaluate the charge motion and the distribution of the fuel mass fraction inside the cylinder before ignition. Different combinations of injected fuel quantities, injection start, engine speed as well as the interaction between fuel and air flow are presented. The results of such optimization regarding the performances of a two-stroke engine with 50 cm3 with gasoline direct injection are a convicting validation of the numerical optimization. Complete paper available under: http://www.sae.org/servlets/productDetail?PROD_TYP=P APER&PROD_CD=1999-01-3286

Concept for Modeling and Optimization of the Mixture Formation using Gasoline Direct Injection in Compact High Speed Engines

The paper presents a concept for modeling and optimization of the mixture formation process during gasoline direct injection, using a high-pressure single fluid injection system which allows the modulation of the injection rate independently on the engine speed. Going from this favorable premise for the adaptation of the mixture formation to various load and speed conditions, the aim of modeling is to find the optimum combination between the adaptable elements as follows: form of the fuel pressure wave, injection timing, spray form, injector location, form of the combustion chamber. Moreover, the interaction between fuel and air flow within the cylinder during the mixture formation is considered as a determining factor for the combustion process, and forms thereby an important part of the modeling. Considering the most advanced GDI strategy, which consists in two stage control of mixture formation – at high load, respectively at low load the paper is focused on the mixture stratification process at low load as extremely sensible problem. The model was generated using the commercial code FLUENT. Different combinations of injected fuel quantity, injection start, engine speed as well as the interaction between fuel and air flow will be presented as time and space related sequences of fuel distribution and velocity within the combustion chamber. The program validation by spray visualization for distinct cases gives the possibility to calibrate the model, for the reliable simulation of a great number of parameter combinations, the extreme configurations being tested on the bench. Complete paper available under: http://www.sae.org/servlets/productDetail?PROD_TYP=PAPE R&PROD_CD=1999-01-2935

Principles for Optimisation of Air Cooling System Applied to the Two-Stroke Engine

The heat transfer process has always played an important role in internal combustion engine design. An area of importance is the thermal loading of engine structural components, and the optimization of engine cooling system. The engine cooling system of a vehicle makes up a significant portion of the total component cost. It also places demands on other vehicle systems, and the quality of its design is evident to the customer in terms of the power that it consumes that for a two-stroke engine with forced convection mr cooling can be also the 10% of the total brake power. An area of importance is the calculation of the thermal load of engine structural components, and the optimization of engine cooling system. Optimization of engine cooling requires the solution of the coupled problem of heat transfer from gases to walls and of heat convection from the structure (generally a finned surface) to the external environment. The aim of this work is to furnish some reference data about the heat transfer process and to fix some criteria to optimize the air cooling system, paying attention to the field of small displacement (50--250 cm{sup 3}) two-stroke engines.

Aspects of Mixture Formation and Combustion in GDI Engines

The internal mixture formation within SI engines using fuel direct injection has a significant potential regarding the reduction of bsfc and pollutant emission. However the short time available for injection and spray distribution, as well as the complexity of the fluid dynamic conditions, amplified in a wide load and speed range, form a different base for the combustion process than using external mixture formation. The intend of the present study is to develop a method for modeling and optimization of mixture formation and combustion using a general approach for the fuel direct injection, which consist in the modulation of the injection rate, independently on the engine speed. In the first stage of modeling, the optimum combination between mixture formation elements as fuel pressure history, injection timing, spray characteristics, injector location or combustion chamber design is of great importance, forming the conditions for the subsequent combustion process. Moreover the interaction between fuel and air flow within the cylinder during the mixture formation is determining for the flame propagation. The model was developed in base of the commercial code FLUENT. Different combinations of fuel quantity, injection timing, fuel/air interaction and engine speed are represented as timeand spacerelated sequences of mixture formation. The program calibration is made by spray visualization for distinct cases, as a base of reliable simulation in a wide range of parameters. Complete paper available under: http://www.sae.org/servlets/productDetail?PROD_T YP=PAPER&PROD_CD=2000-01-0648

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