Marco Chiodi

Calculating the thermodynamic properties of burnt gas and vapor fuel for user-defined fuels

For real working-process simulations it is essential to know the caloric properties of the working fluid, such as the specific enthalpy and the real gas constant. When using standard-fuels there are established models which describe the caloric variables as functions of temperature, air/fuel-ratio and pressure. In each case, these models were developed for a certain fuel composition and their application to alternative fuels is limited or not valid at all. Thus, an approach is discussed, which is valid for any user-defined fuel.For real working-process simulations it is essential to know the caloric properties of the working fluid, such as the specific enthalpy and the real gas constant. When using standard-fuels there are established models which describe the caloric variables as functions of temperature, air/fuel-ratio and pressure. In each case, these models were developed for a certain fuel composition and their application to alternative fuels is limited or not valid at all. Thus, an approach is discussed, which is valid for any user-defined fuel.

GDI Swirl Injector Spray Simulation:A Combined Phenomenological-CFD Approach

In this work the formation and the evolution of the fuel spray emerging from a hollow-cone swirl injector were investigated. The first aim of the work was to set up a tool for fuel spray simulation in a CFD analysis that can offer a reasonable accuracy with no significant increment in the computational time. The analysis started from a theoretical formulation of the fuel flow inside the injector, based on the potential theory, obtaining an injector model which allows the calculation of the main spray characteristics usually required by the CFD analysis (i.e. droplet velocity, fuel film thickness, droplet size distribution). These parameters can be obtained only from spray cone angle and mass flow rate, which are the data commonly provided by injector manufacturers. Furthermore, a phenomenological approach was also presented, in order to properly simulate in CFD analysis the spray tip penetration in the dense spray zone, without requiring an increase of the spatial grid resolution. Encouraging results were obtained that are in good agreement with the experimental data.

Berechnung der thermodynamischen Stoffwerte von Rauchgas und Kraftstoffdampf beliebiger Kraftstoffe

For real working-process simulations it is essential to know the caloric properties of the working fluid, such as the specific enthalpy and the real gas constant. When using standard-fuels there are established models which describe the caloric variables as functions of temperature, air/fuel-ratio and pressure. In each case, these models were developed for a certain fuel composition and their application to alternative fuels is limited or not valid at all. Thus, an approach is discussed, which is valid for any user-defined fuel.For real working-process simulations it is essential to know the caloric properties of the working fluid, such as the specific enthalpy and the real gas constant. When using standard-fuels there are established models which describe the caloric variables as functions of temperature, air/fuel-ratio and pressure. In each case, these models were developed for a certain fuel composition and their application to alternative fuels is limited or not valid at all. Thus, an approach is discussed, which is valid for any user-defined fuel.

3D-CFD analysis on scavenging and mixture formation for CNG direct injection with an outward-opening nozzle

On the basis of comprehensive experimental measurements, 3D-CFD analyses of CNG direct injection, using an outward-opening nozzle, were performed. Main objective of the presented work was the examination of influencing factors on the hollowcone jet propagation, fuel distribution and therewith directly associated back flow into the intake manifolds.

Investigation of the mixture formation process with combined injection strategies in high-performance SI-engines

An SI-race engine’s performance depends largely on how the combustible mixture is formed. In light of severely restrictive technical regulations of the various racing series, the optimization of the mixture formation process is one of the few remaining ways to increase engine performance. Being the predominant injection strategies in SI engines, both direct injection (DI) at high fuel pressures and port fuel injection (PFI) with much lower fuel pressures show intrinsic advantages. Hence, the potential of a combination of said injection strategies in the context of a motorsports application was investigated in a joint effort by means of both an experimental and a numerical approach. The former was carried out at the Institute of Internal Combustion Engines of the Technische Universitat Munchen (TUM). The latter, a 3d-CFD-simulation of the gas exchange and mixture formation process, was conducted by the Forschungsinstitut fur Kraftfahrwesen und Fahrzeugmotoren Stuttgart (FKFS). As the preliminary investigations revealed, the combination of said injection strategies seems to have increased engine performance by a marginal yet measurable amount, thus supporting the initial assumption that in a motorsports application the otherwise superior DI injection strategy has its limitations. Subsequently, the focus of this paper is to conduct a more thorough analysis to deepen the understanding of a combined injection system’s impact on the mixture formation process.

Stoffwerte von Rauchgas und Kraftstoffdampf beliebiger Kraftstoffe

Fur die Motorprozessrechnung ist die Kenntnis der kalorischen Stoffgrosen des Arbeitsgases von elementarer Bedeutung. Fur Standardkraftstoffe gibt es hierfur etablierte Modelle, die diese Grosen als Funktion von Temperatur, Druck und Luftverhaltnis beschreiben. Allerdings wurden diese Ansatze jeweils fur eine ganz bestimmte Kraftstoffzusammensetzung aufgestellt, und ihre Ubertragbarkeit auf alternative Kraftstoffe ist begrenzt oder nicht zulassig. Deshalb wurde am FKFS ein Ansatz fur beliebige Kraftstoffe entwickelt.

Development and Experimental Investigation of a Two-Stroke Opposed-Piston Free-Piston Engine

The proposed paper deals with the development process and initial measurement results of an opposed-piston combustion engine for application in a Free-Piston Linear Generator (FPLG). The FPLG, which is being developed at the German Aerospace Center (DLR), is an innovative internal combustion engine for a fuel based electrical power supply. With its arrangement, the pistons freely oscillate between the compression chamber of the combustion unit and a gas spring with no mechanical coupling like a crank shaft. Linear alternators convert the kinetic energy of the moving piston into electric energy. The virtual development of the novel combustion system is divided into two stages: On the one hand, the combustion system including e.g. a cylinder liner, pistons, cooling and lubrication concepts has to be developed. On the other hand, 3D-CFD-simulations are used in the early stage within the virtual development process toward the optimization of the geometry of the scavenging ports and ducts, the gas exchange, injection and ignition. With the high variability of the free piston concept, a strategy for a dual combustion mode operation with spark ignition and HCCI is developed. The new engine is constructed on and implemented at the hydraulic free-piston test bench at DLR and was successfully taken into operation. First measurement results show the engine behavior with dual spark ignition and two opposed injectors.

Modeling of a map based turbocharger in a three dimensional engine environment

The ongoing trend towards downsized engines with turbocharger intensifies the need for development tools capable of simulating complex engine layouts with a level of details that only multidimensional models offer. This is strongly driven by stringent emission limits and the effort to reduce CO2 emissions while ensuring the concurrently demanded vehicle performance. In turbocharged engines the coupling of the combustion chamber and turbocharger forms a complex system in which the components influence each other remarkably causing e.g. the well-known turbo-lag.

Virtuelle Motorentwicklung als Erfolgsfaktor in der F.I.A. Rallye-Weltmeisterschaft (WRC)

Im Bemuhen um stetige Leistungssteigerung sowie der Optimierung von Wirkungsgrad und Ansprechverhalten, unterliegt der Motorentwicklungsprozess im Rennsport erheblichem Zeit- und Kostendruck. Gezielt eingesetzte 3D-CFD-Simulationen konnen diesen Entwicklungsprozess masgeblich unterstutzen, indem das Verstandnis fur innermotorische Vorgange (Kraftstoffeinspritzung und -vermischung, Verbrennung, Wandwarmeubergang, usw.) sowie deren Beeinflussung durch Motor-Geometrien und Steuerungsstrategien verbessert wird.