Publikationen / Ergebnisse
(Deutsch)
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Dieses Projekt strebt an, bestehende Simulationswerkzeuge zu erweitern um neuartigen Brennverfahren und unterschiedlichen Kraftstoffeigenschaften Rechnung tragen zu können und präzise Vorhersagen zu ermöglichen. Zu diesem Zwecke werden in Zusammenarbeit mit anderen nationalen und internationalen Forschungsvorhaben wertvolle Synergien genutzt. Die Problematik wird dabei von vier Seiten angegangen: Jeweils paarweise ein experimenteller Teil zur Bereitstellung der Validierungdaten und parallel dazu die Simulations-Code Entwicklungsarbeit. Die zweite „Achse“ besteht in der gezielten Ausnutzung der jeweiligen Vorteile von motorischen Versuchsträgern (welche die Validierung an technisch relevanten Verbrennungvorgängen erlaubt anhand globaler Grössen wie bspw. Zylinderdruck) und von ‚generischen‘ Experimenten an optisch zugänglichen Verbrennungskammern und Einhubtriebwerken (welche zusätzlich wertvolle, örtlich aufgelöste Informationen liefern für die Submodellvalidierung und –kalibrierung).
In 2008 konnte am LAV ein MTU 396 Einzylinder heavy duty Forschungsmotor erfolgreich in Betrieb genommen werden welcher einen flexiblen Austausch der Instrumentierung zulässt (schnelle Entnahmesonde, Mehrwellenpyrometrie, Ionenstrom-Sonden etc.). Der bestehende Conditional Moment Closure code wurde mittels Daten eines vorher ausgemessenen heavy-duty Motors für einen weiten Bereich von Betriebsbedingungen erfolgreich weiter-validiert anhand von Druckverläufen, Brennraten und NOx Emissionen, dies für konventionellen Dieselkraftstoff. Letztere Untersuchung wurde zur Publikation eingereicht für den SAE World Congress im April 2009.
Erste Modifikationen für die Inbetriebnahme des Einhubtriebwerkes im ‚dual-fuel‘-Betrieb, d.h. mit homogener Grundladung und Zündung mittels Dieselpilot sind erfolgt und eine umfangreiche Literaturstudie zu diesem Brennverfahren weitgehend abgeschlossen. Aufgrund von Rekrutierungsschwierigkeiten konnten auf der Seite der Kraftstoffvariationen noch keine Messungen durchgeführt werden, alle vorbereitenden Arbeiten sind weitestgehend abgeschlossen und die Infrastruktur und Messausrüstung steht ebenfalls bereit; Evaluationen und Interviews mit potentiellen Kandidaten erfolgen laufend.
Im nächsten Jahr wird der Schwerpunkt der Arbeit an der Generierung experimenteller Daten an den verschiedenen Versuchsträgern liegen, wobei die Simulation begleitend ausgebaut wird.
Auftragnehmer/Contractant/Contraente/Contractor:
ETH Zentrum, Institut für Energietechnik, Laboratorium für Aerothermochemie und Verbrennung
Autorschaft/Auteurs/Autori/Authors:
Wright,Yuri M.
Boulouchos,Konstantinos
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Schlussbericht
(Englisch)
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The availability of predictive simulation tools has become indispensable in the optimization process of combustion devices. This project is directed towards the further improvement of a ‚high-fidelity‘ numer-ical model for fuel spray combustion, with particular emphasis on improvements of the quantitative predictions of heat release and emissions.
To this end, numerical and experimental approaches are combined: On the measurement side, a sin-gle-cylinder heavy-duty research engine has been commissioned and subsequently employed to es-tablish a comprehensive dataset for engine model validation. An in-house high temperature high pres-sure optically accessible ‘generic’ combustion chamber has further been augmented with a hydrogen pre-combustion module, enabling data collection also at higher temperatures and for a broader range of fuels. Further data characterizing auto-ignition events of Diesel pilot sprays in lean premixed me-thane charges and subsequent flame propagation (dual fuel combustion) has been acquired by means of an in-house rapid compression/expansion machine with optical access.
The data-sets from these in-house experiments carried out during the course of this project are further supplemented by data from a large marine engine reference experiment installed at an industry part-ner (Wärtsilä Switzerland Ltd.) and additional data-sets documented in the literature. Based on this information, in-depth validation and further development of the Conditional Moment Closure (CMC) combustion model has been performed. The findings reported suggest that the model can capture a wide range of physical processes occurring in spray autoignition. As a consequence, the model is capable of providing excellent qualitative and to large extent very good quantitative predictions of igni-tion delays and locations, flame lift-off heights, heat release rates/pressure rise as well as NOx emis-sions and soot volume fraction distributions.
The project is structured in five work packages (APs), some of which are subdivided in an experi-mental and numerical part. These are summarized briefly as follows:
AP1: A heavy-duty single cylinder engine test rig with well-defined intake and exhaust plenum condi-tions has been commissioned and subsequently employed to generate a comprehensive dataset for model validation. Variations include on the one hand changes in the air path, i.e. air temperature and pressure combinations, especially also towards low temperature conditions typical for Miller valve timings. Secondly, the influence of parameters relating to the fuel path have been systematically in-vestigated, in particular the effect of injection pressure and injection strategies, which including piloted injections. The assembled matrix constitutes a highly challenging dataset for combustion and emission models. This data and the test rig will be used in two approved follow-up projects of the Swiss Innova-tion promotion agency (KTI) and the Competence Centre Energy and Mobility (CCEM) for further ex-perimental investigations as well as model validation and development.
In work package AP2a, the influence of the fuel composition on the injection process, spray formation, ignition and combustion for seven fuels which consist of six Fischer-Tropsch fuels (with varying paraf-finic, olefinic, naphthenic and aromatic contents) plus a reference Diesel synthetic has been character-ised by means of experiments carried out in the optically accessible high pressure and temperature cell (HTDZ) of LAV. In order to reach the high gas temperatures required for short ignition delays comparable to those found in Diesel engines, the test rig has further been supplemented with a new Hydrogen pre-combustion module in this project. The project was co-funded by the successfully com-pleted project „Future Fuels Diesel“ of the Forschungs-Vereinigung Verbrennungskraftmaschinen (FVV).
AP2b and AP4b: Experiments with diesel spray pilot injection in a methane air mixture under various conditions have been performed on an optically accessible single stroke machine installed at ETH. Optical and transient data of the dual fuel combustion processes were acquired for different operating conditions. The successful application of the developed combustion model for dual fuel combustion could be shown. Excellent agreement of computed and experimentally obtained ignition delay times as well as ignition locations and initial flame shapes with respect to the amount of methane in the ambient gas mixture is observed. Co-funding for both work packages is provided by two projects of the German FVV namely “Piloteinspritzung” and “Miller/Atkinson”, the former of which has been successfully completed.
AP3: This package consists of model validation by means of the broad range of experimental data from an the-house heavy-duty engine, the single stroke rapid compression/expansion machine and four different optically accessible spray test rigs of different sizes. In addition to the successful valida-tion of heat release rate predictions, ignition timing and location, flame lift-off heights for the generic test rigs, sensitivity analyses have been reported to various sub-models and uncertainties in the boundary conditions stemming from the experiment. Furthermore, on the emission side, qualitative trends of NOx emission have been demonstrated for the heavy-duty engine for a range of operating conditions and the influence of EGR is well reproduced. In addition the model has successfully been extended by a two-equation soot model implemented in the CMC context. Excellent predictions of soot volume fraction distributions are reported for a broad range of oxygen contents at two different engine relevant pressures.
AP4a: As part of AP4a, measurements from a medium speed diesel engine (Wärtsilä 6L20) have been used to study ignition delay as a function of in-cylinder conditions during injection. Particular emphasis is placed on conditions with different Miller valve timings and two-stage turbo-charging con-figurations, resulting in very broad temperature and pressure ranges. A correlation for ignition delays for this broad range of operating conditions has been successfully developed, based on a three-Arrhenius model which was developed in the framework of the FVV project “Kraftstoffkennzahlen” using shock tube data and co-funded by the Swiss Office of Energy (BfE). The engine is part of the CCEM-LERF engine test-bed, located in PSI, Villigen, and is further co-funded by the CCEM - CELaDE and EU FP7 HERCULES-B projects.
AP5: Publication and reporting has been carried out in parallel to the work packages and resulted in several peer reviewed journal publications and a number of conference proceedings. In addition, an-nual and intermediate reports have been provided to the Swiss Office of Energy (BfE).
Auftragnehmer/Contractant/Contraente/Contractor:
ETH Zentrum, Institut für Energietechnik, Laboratorium für Aerothermochemie und Verbrennung
Autorschaft/Auteurs/Autori/Authors:
Wright,Yuri M.
Bolla,Michele
Kyrtatos,Panagiotis
Obrecht,Peter
Schlatter,Stéphanie
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