Franz Chmela

Advanced Heat Transfer Model for CI Engines

A realistic simulation of the wall heat transfer is an imperative condition for the accurate analysis and simulation of the working process of IC engines. Due to its simplicity in application, zero-dimensional wall heat transfer models dominate engine cycle simulation in practice. However, experience shows that existing zero-dimensional models for wall heat transfer do not yield satisfactory results in certain applications. This is mainly due to a lack of consideration of the actual flow field in the cylinder. In this paper a quasi-dimensional heat transfer model, which is based on a detailed description of the turbulent flow field in the combustion chamber, is described. The model presents a consistent approach for the high pressure as well as the low pressure part of the cycle. The results of the heat transfer model are compared with results from the correlation by Woschni/Huber and with experimental results from various Dl Diesel engines.

Die Vorausberechnung des Brennverlaufs von Dieselmotoren mit direkter Einspritzung auf der Basis des Einspritzverlaufs

Unter der Annahme einer ausschlieslich mischungsgesteuerten Verbrennung wurde im Rahmen der Verbrennungsforschung der AVL ein neuer nulldimensionaler Ansatz fur den Brennverlauf von Dieselmotoren mit Direkteinspritzung entwickelt (MCC-Ansatz). Mit diesem auf der kinetischen Strahlenergie basierenden Ansatz sind schon wahrend der Konstruktionsphase Vorausrechnungen des Brennverlaufs aus Simulationsdaten uber Einspritzdruckverlauf und Nadelhubverlauf moglich. Ein weiteres Anwendungsgebiet ist die Analyse von realen Brennverlaufen. Die Kenntnis des funktionalen Zusammenhangs zwischen Einspritzvorgang und Brennverlauf kann auch zur Ruckrechnung der Einspritzparameter aus einem gewunschten Brennverlauf genutzt werden.

Emissionsverbesserung an Dieselmotoren mit Direkteinspritzung mittels Einspritzverlaufsformung

Der vorliegende Bericht ist das wissenschaftliche Ergebnis einer Forschungsaufgabe, die von der Forschungsvereinigung Verbrennungskraftmaschinen e.V. (FVV, Frankfurt) gestellt und von der AVL List GmbH bearbeitet wurde. Das wesentliche Ziel des Forschungsvorhabens war es, eine genauere Kenntnis der Zusammenhange zwischen dem Einspritzvorgang einerseits und den Abgasemissionen sowie dem spezifischen Kraftstoffverbrauch andererseits zu gewinnen. Die Durchfuhrung der Arbeiten gliederte sich in drei Abschnitte, namlich in die Adaption des Brennverfahrens, in die Untersuchung verschiedenster Varianten der Einspritzratenformung und schlieslich in die Ausschopfung des Verbesserungspotentials der Einspritzverlaufsformung durch die Hinzufugung der Abgasruckfuhrung.

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.

Parameter Based Combustion Model for Large Prechamber Gas Engines

Challenging requirements for modern large engines regarding power output, fuel consumption, and emissions can only be achieved with carefully adapted combustion systems. With the improvement of simulation methods simulation work is playing a more and more important role for the engine development. Due to their simplicity and short computing time, one-dimensional and zero-dimensional calculation methods are widely applied for the engine cycle simulation and optimization. While the gas dynamic processes in the intake and exhaust systems can already be simulated with sufficient precision, it still represents a considerable difficulty to predict the combustion process exactly. In this contribution, an empirical combustion model for large prechamber gas engines is presented, which was evolved based on measurements on a single cylinder research engine using the design of experiment method. The combustion process in prechamber gas engines is investigated and reproduced successfully by means of a double-vibe function. The mathematical relationship between the engine operating parameters and the parameters of the double-vibe function was determined as a transfer model on the base of comprehensive measurements. The effects of engine operating parameters, e.g., boost pressure, charge temperature, ignition timing, and air/fuel ratio on the combustion process are taken into account in the transfer model. After adding modification functions, the model can be applied to gas engines operated with various gas fuels taking into account the actual air humidity. Comprehensive verifications were conducted on a single-cylinder engine as well as on full-scale engines. With the combination of the combustion model and a gas exchange simulation model the engine performance has been predicted satisfactorily. Due to the simple phenomenological structure of the model, a user-friendly model application and a short computing time is achieved.

Integration von Simulationswerkzeugen zur Optimierung von Motorkonzepten

Der folgende Beitrag der AVL List GmbH befasst sich mit einer integrierten Anwendung von Simulationswerkzeugen zur Festlegung des Motorkonzepts und Optimierung der Thermodynamik-Auslegung. Es werden die drei wesentlichen Schritte der Vorgangsweise, Parameter-Spezifikation, Ausfuhrung der Variationsrechnung und automatisierte Optimierung beschrieben. Zur umfassenden Darstellung der innermotorischen Vorgange werden neue beziehungsweise verbesserte Simulationsansatzefur die Verbrennung, die Stickoxidbildung und den Warmeubergang benutzt.Verifikationsbeispiele belegen die Aussagefahigkeit der eingesetzten Berechnungsmodelle. Anhand der Erstellung eines Motorkonzepts wird die Arbeitsweise der Auslegungsmethode verdeutlicht.

Parameter Based Combustion Model for Large Pre-Chamber Gas Engines

Challenging requirements for modern large engines regarding power output, fuel consumption and emissions can only be achieved with carefully adapted combustion systems. With the improvement of simulation methods simulation work is playing a more and more important role for the engine development. Due to their simplicity and short computing time, one-dimensional and zero-dimensional calculation methods are widely applied for the engine cycle simulation and optimization. While the gas dynamic processes in the intake and exhaust system can already be simulated with sufficient precision, it still represents a considerable difficulty to predict the combustion process exactly. In this contribution, an empirical combustion model for large pre-chamber gas engines is presented, which was evolved based on measurements on a single cylinder research engine using the DOE (Design of Experiments) method. The combustion process in pre-chamber gas engines is investigated and reproduced successfully by means of a Double-Vibe function. The mathematical relationship between the engine operating parameters and the parameters of the Double-Vibe function was determined as a transfer model on the base of comprehensive measurements. The effects of engine operating parameters e.g. boost pressure, charge temperature, ignition timing, air/fuel ratio on the combustion process are taken into account in the transfer model. After adding modification functions, the model can be applied to gas engines operated with various gas fuels taking into account the actual air humidity. Comprehensive verifications were conducted on a single cylinder engine as well as on full scale engines. With the combination of the combustion model and a gas exchange simulation model the engine performance has been predicted satisfactorily. Due to the simple phenomenological structure of the model, a user-friendly model application and a short computing time is achieved.© 2009 ASME

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.