Gerhard Pirker

Konsistente Methodik zur Vorausrechnung der Verbrennung in Kolbenkraftmaschinen

Neben den heute weithin verwendeten Software-Paketen fur die dreidimensionale Simulation von Stromung, Gemischbildung und Verbrennung im Motor gibt es besonders zur Vor-Optimierung von Motorgeometrie und Betriebsparametern einen Bedarf an einfacher und schneller zu bedienenden Simulationstools. Das Kompetenzzentrum fur umweltfreundliche Stationarmotoren (Large Engines Competence Center, LEC) in Graz hat es sich zur Aufgabe gemacht, fur die besonders bei Grosmotoren beachtliche Vielfalt an Kraftstoffen und Verbrennungsverfahren eine konsistente Simulationsmethodik auf der Basis von null-dimensionalen Modellansatzen zu entwickeln.

Influence of Cavitation in the Injection Nozzle on Combustion in Diesel Engines

This paper is concerned with the influence of cavitation in the injection nozzle on combustion in diesel engines. After an overview of the fundamental definitions to characterize nozzles — where above all the injection pressure, the back pressure, the injection mass flow, and the spray momentum through the nozzle as well as the geometry play a role — the difference between a cavitating and a non-cavitating nozzle will be clarified both theoretically and based on engine measurements. To observe the influence of cavitation on combustion in isolation, a cavitating and a non-cavitating nozzle were designed in such a way that they possessed the same mass flow and the same nozzle discharge velocity. In addition to the manufacturers measurement, the nozzles were measured using a combined flowrate—spray momentum device at levels of injection pressure and back pressure close to those in an engine. A single-cylinder research engine with a modern common rail injection system served as the test engine for the experiments. The experiments revealed striking differences in emission levels. Especially notable are the differences in the soot values. To explore in more detail these differences between the cavitating and non-cavitating nozzle, optical investigations were conducted in an injection chamber. CCD high-speed imaging was used to visualize mixture formation of the two different nozzles.

Simulation Based Development of Combustion Concepts for Large Diesel Engines

The development of low-emission combustion concepts for large Diesel engines requires a specially adapted methodology. In all phases of the development process, it is essential that appropriate tools are used so that an optimized solution can be found within a short time. This paper will describe the methodology used for developing combustion concepts for large Diesel engines. In general, the development of a combustion concept for Diesel engines comprises the definition of the system (e.g. combustion chamber geometry, injection system, EGR system and charging system) and the calibration of engine parameters (e.g. injection parameters, EGR rate, charge pressure, excess air ratio and valve timing) for an application and its emission scenario. In the present case, the main objective was to develop concepts for applications to comply with emissions standards according to EU Stage III B and US EPA Tier 4. To this end, the LEC has developed the LDM method (LEC Development Methodology). This method is based on the intensive interaction of simulation with experimental investigations on single-cylinder research engines. As part of this development methodology, 3D CFD simulation as well as 0D and 1D engine cycle calculation are employed. Another approach used to handle the complexity of the systems is Design of Experiments (DoE) for simulation and experimental work. While 3D CFD simulation is used to optimize the details of the combustion and pollutant formation processes in the combustion chamber, 0D and 1D engine cycle simulation is applied to select the concepts and to pre-optimize important engine parameters. One great advantage of 0D and 1D models is their short calculation time, which allows the investigation of a great amount of variations in parameters. In order to apply the methodology, it must be guaranteed that the results from tests on the single-cylinder engine (SCE) can be transferred to the multi-cylinder engine (MCE). Therefore, it is necessary that the boundary conditions of the SCE are comparable to those of the MCE. Not only the same thermal boundary conditions but also the same conditions at the beginning of the high-pressure cycle (charge composition, pressure and temperature) must be maintained. The SCE measurement results that are generated serve to verify and calibrate the simulation models and deliver the necessary boundary conditions for further simulations. All in all, the paper comprises an evaluation of the different simulation models used and the applied development methodology in order to optimize fuel consumption and to reduce the emissions of large Diesel engines.Copyright

A new approach for combustion modeling of large dual-fuel engines

Until several years ago, large engines were primarily developed for single fuel operation, which has resulted in the availability of optimized gas and diesel combustion concepts. Today large engines are subject to new requirements that go beyond merely enhancing existing concepts. In a wide variety of areas of application, the focus is not only on attaining the highest efficiency with the lowest possible emissions but also on attaining the greatest possible flexibility in terms of fuel.

A consistent simulation methodology for combustion in piston engines

Along with the widely used software packages for three-dimensional simulation of flow, mixture formation, and combustion in engines, there is a need for simpler and faster-to-handle simulation tools especially for the preoptimisation of engine geometry and operating parameters. The Large Engines Competence Center (LEC) in Graz, Austria, has developed a consistent zero-dimensional simulation methodology for the particularly at large engines considerable variety of fuels and combustion systems.

Verbrennungsmodelle für Großgasmotoren

Null‐ und eindimensionale Simulationsmodelle sind insbesondere fur die Prognose der Eigenschaften eines Motors schon wahrend der Auslegungsphase geeignet. Bei Ottogasmotoren besteht die Herausforderung, dass eine Vielzahl von Brennverfahren und Kraftstoffen abzubilden sind. Um die Entwicklung von immer neuen Simulationsmodellen fur diese Spezialfalle vermeiden zu konnen, ist es nutzlich, eine moglichst allgemeingultige Modellierung zur Verfugung zu haben. Ein hohes Mas an Allgemeingultigkeit kann von Modellen erwartet werden, die weitgehend auf physikalischen Gesetzen beruhen und nur ein geringes Mas an Phanomenologie enthalten. Zu diesem Zweck wurde am LEC eine konsistente Simulationsmethodik entwickelt, die diesen Bedingungen genugt (vgl. Chmela et al. 2006, 2008). Eine Ubersicht uber die am LEC zur Modellierung der Vorgange im Gasmotor verfugbaren Simulationsmodelle findet sich in Abb. 45.1.

Modellierung des Ladungswechsels

Die Berechnung des Ladungswechsels ist fur thermodynamische Betrachtungen des Arbeitsprozesses von besonderer Bedeutung, da damit wichtige Eingangsgrosen fur die Analyse des Zylinderdruckverlaufs (Brennverlaufsauswertung, Verlustteilung …), wie Restgasgehalt und Ladungsmasse bei Einlassschluss, die entscheidend fur die Hochdruckrechnung sind, ermittelt werden konnen. Grundsatzlich konnen fur die Berechnung des Ladungswechsels folgende nulldimensionale Methoden eingesetzt werden: