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Neat Oxymethylene Ethers: Combustion Performance and Emissions of OME2, OME3, OME4 and OME5 in a Single-Cylinder Diesel Engine

Technical University of Munich-Patrick Dworschak, Vinicius Berger, Martin Härtl, Georg Wachtmeister
  • Technical Paper
  • 2020-01-0805
To be published on 2020-04-14 by SAE International in United States
Diesel engines are arguably the superior device in the ground transportation sector in terms of efficiency and reliability, but suffer from inferior emission performance due to the diffusive nature of diesel combustion. Great research efforts gradually reduced nitrogen oxide (NOX) and particulate matter (PM) emissions, but the PM-NOX trade-off remained to be a problem of major concern and was believed to be inevitable for a long time. In the process of engine development, the modification of fuel properties has lately gained great attention. In particular, the oxygenate fuel oxymethylene ether (OME) has proven potential to not only drastically reduce emissions, but possibly resolve the formerly inevitable trade-off completely. Although intensified investigations with OME were conducted within the past decade, little is known about the specific influence of fuel properties inherent to unimolecular, high chain length OME on combustion characteristics, emission performance and particle size. The latter is of special concern, as studies on oxygenate fuels reported increased formation of nanoparticles, which are known to have adverse effects on human health. In this paper, the authors…
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The potential of gasoline fueled pre-chamber ignition combined with elevated compression ratio

Hitachi Europe GmbH-Henning Sauerland
Technische Universitat Munchen-Andreas Stadler, Martin Härtl, Georg Wachtmeister
  • Technical Paper
  • 2020-01-0279
To be published on 2020-04-14 by SAE International in United States
A challenge in today’s automotive combustion research is to increase the thermal efficiency and to meet ever more stringent emission regulations at the same time. In this study, a single cylinder research engine is equipped with a tailored pre-chamber ignition system and operated at two different compression ratios, namely 10.5 and 14.2. Different pre-chamber design variants are evaluated considering both unfueled and gasoline-fueled operation. As for the latter, the influence of the fuel amount supplied to the pre-chamber is discussed. Due to its principle, the pre-chamber ignition system increases combustion speeds by generating enhanced in cylinder turbulence and multiple ignition sites. This property proves to be an effective measure to mitigate knocking effects. It is shown that less spark retard compared to conventional spark ignition allows to exploit the efficiency benefit of elevated compression ratios also in high load operation for stoichiometric mixtures. Furthermore, auxiliary fueling of the pre-chamber enables ultra-lean combustion (λ=2.0) with very low NOx emission levels. Apart from decreased throttling losses lean burn assists to further suppress knocking in case of elevated…
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A New Cavitation Algorithm to Support the Interpretation of LIF Measurements of Piston Rings

Technical University of Munich-Georg Wachtmeister
Technical University of Munich / Tenneco-Fabian H. Ruch
  • Technical Paper
  • 2020-01-1091
To be published on 2020-04-14 by SAE International in United States
To investigate oil transport mechanisms under real engine conditions, laser induced fluorescence (LIF) is used. The engine oil is mixed with a dye that can be induced by a laser. The emitted light intensity from the dye correlates with the residual oil at the sensor position and resulting oil film thicknesses can be determined in high detail for each crank angle. However, the general expectation is not always achieved, e.g. an exact representation of piston ring barrel shapes. In order to investigate the responsible lubrication effects of this behavior, a new cavitation algorithm for the Reynolds equation has been developed. The solution retains the mass conservation and does not use any switch function in its mathematical approach. In contrast to common approaches, no vapor-liquid ratio is used, but one or several bigger bubbles are approximated, as have been observed in other experiments already. As a result, not only the known boundary conditions for the Reynolds equation become unnecessary, but the solution also gives a clearer idea about the shape of the cavitation bubble. The combination…
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Development of a Measuring System for the Visualization of the Oil Film between the Piston and Cylinder Liner of a Gasoline Engine

SAE International Journal of Engines

Technical University of Munich, Germany-Julian Schäffer, Claus Kirner, Martin Härtl, Georg Wachtmeister
  • Journal Article
  • 03-13-02-0013
Published 2019-11-14 by SAE International in United States
The design of cylinder liners, pistons, and piston rings is subject to different conflicting goals. In addition to a loss-free seal of the combustion chamber, sufficient oil must be present between the friction partners. Both the reduction of piston assembly friction and the minimization of oil consumption are crucial to achieve the strictly defined CO2 and emission standards. To master this challenge and find the best compromise requires a lot of system-specific know-how. The automobile and engine manufacturers focus mainly on friction-reducing measures, which are analyzed with different measuring methods such as the floating-liner method, the strip-down method, or the instantaneous indicated mean effective pressure (IMEP) method. However, the interpretation of the results and the development of realistic simulation models lacks information about the oil film behavior and the film thickness. In order to gain this missing knowledge, instruments for oil film visualization and oil film thickness measurement have to be developed. In the FVV-project “Piston ring oil transport - Glassliner”, the two-dimensional laser-induced fluorescence method (2D-LIF) is used to visualize the lubricating oil film…
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Experimental Analysis of Gasoline Direct Injector Tip Wetting

SAE International Journal of Engines

Technical University of Munich, Germany-Fabian Backes, Sebastian Blochum, Martin Härtl, Georg Wachtmeister
  • Journal Article
  • 03-13-01-0006
Published 2019-10-14 by SAE International in United States
At gasoline direct injection, light-duty engines operated with homogeneous, stoichiometric combustion mode, particulate emissions are mainly formed in diffusion flames that result from prior fuel wall wetting. Besides the piston, liner, and intake valves, the injector tip acts as a main particulate source when fuel is adhered to it during an injection. Hence, this injector tip fuel wetting process and influences on this process need to be analyzed and understood to reduce engine-out particulate emissions. The present work analyzes the injector tip wetting process in an experimental way with a high-speed and high-resolution measurement system at an optically accessible pressure chamber. The performed measurements reveal that injector tip wetting can occur during the complete injection event by different mechanisms. Large spray cone angles at start and at end of injection or distortions of the spray result in direct contact of the fuel spray with the step-hole wall. Additionally, fuel accumulates during an injection in the step-hole volume and discharges onto the injector tip surface subsequently. Furthermore, a poor primary breakup at end of injection can…
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Virtual Investigation of Real Fuels by Means of 3D-CFD Engine Simulations

FKFS-Francesco Cupo, Marco Chiodi
Technical Univ of Munich-Daniel Koch, Georg Wachtmeister
  • Technical Paper
  • 2019-24-0090
Published 2019-09-09 by SAE International in United States
The reduction of both harmful emissions (CO, HC, NOx, etc.) and gases responsible for greenhouse effects (especially CO2) are mandatory aspects to be considered in the development process of any kind of propulsion concept. Focusing on ICEs, the main development topics are today not only the reduction of harmful emissions, increase of thermodynamic efficiency, etc. but also the decarbonization of fuels which offers the highest potential for the reduction of CO2 emissions. Accordingly, the development of future ICEs will be closely linked to the development of CO2 neutral fuels (e.g. biofuels and e-fuels) as they will be part of a common development process. This implies an increase in development complexity, which needs the support of engine simulations. In this work, the virtual modeling of real fuel behavior is addressed to improve current simulation capabilities in studying how a specific composition can affect the engine performance. The goal is to create a series of models that allow to virtually investigate different fuels and to minimize, as much as possible, the costly and time-consuming experimental tests. In…
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Gasoline Fueled Pre-Chamber Ignition System for a Light-Duty Passenger Car Engine with Extended Lean Limit

SAE International Journal of Engines

Technische Universitat München, Germany-Andreas Stadler, Maximilian Wessoly, Sebastian Blochum, Martin Härtl, Georg Wachtmeister
  • Journal Article
  • 03-12-03-0022
Published 2019-06-07 by SAE International in United States
In this work, a light-duty research engine based on a passenger car engine is equipped with an in-house developed pre-chamber (PC) ignition system replacing the conventional spark plug. By using such kind of ignition system, the combustion in the main chamber is enhanced by radical seeding through jets travelling from the pre-chamber to the main chamber. These radicals serve as high-energy ignition sites for the mixture in the main combustion chamber leading to enhanced burn rates and combustion speed. In contrast to conventional spark-ignited combustion starting from the spot of the electrode gap, an extended lean misfire limit and a mitigated knocking tendency are achieved. The presence of a gasoline direct injector inside the PC enables the system to operate in both passive and active mode. The injection of a small fuel amount allows separating the air-to-fuel equivalence ratio of the pre-chamber and the main chamber. By this, an overall lean mixture is ignited by providing a stoichiometric mixture near the PC spark plug. In this study, different orifice nozzles of the PC are investigated…
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Conceptual Investigations on Full Optical Accessibility to Large-Bore Medium-Speed Engines

SAE International Journal of Engines

TUM LVK, Germany-Stephan Bernhard Karmann, Maximilian Prager, Georg Wachtmeister
  • Journal Article
  • 03-12-03-0020
Published 2019-05-15 by SAE International in United States
Optically accessible engines are an essential tool to investigate the combustion process in internal combustion engines via optical and laser optical methods. These methods can be applied to analyze the mixing formation, injection, combustion, and emission formation in situ for a better understanding of the combustion process. The derived findings result in new potentials for increased efficiency and reduced emissions. While the application for passenger car- and truck-size engines is quite common, the application of such an optically accessible engine is rather rare for large-bore engines driving ships or power plants due to their huge scale. The following sections show a conceptual design study to make a large-bore dual-fuel (DF) engine with a bore of 350 mm and stroke of 440 mm fully optically accessible according to the Bowditch principle. As the layout was based on an already existing and working engine of the same principle but half the bore, numerical investigations of the critical parts of the presented large-scale fully optical engine were carried out to consolidate the feasibility of the design study. On…
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Compensation Strategies for Aging Effects of Common-Rail Injector Nozzles

Technical University of Munich-Sebastian Schuckert, Mark Huthmacher, Georg Wachtmeister
Published 2019-04-02 by SAE International in United States
The thermal and emission efficiency of diesel engines depends to a large extent on the quality of fuel injection. However, over engine lifetime, injection rate and quality will change due to adverse nozzle aging effects, such as coking or cavitation. In this study, we discuss the influences of these effects on injection and heat release rate. The injection rates of previously unused nozzles and a nozzle that had been operated in a vehicle engine were compared in order to clarify the impact of aging effects. The key to the detection of alterations of injection nozzles is the identification of strongly correlating parameters. As a first step, an instrumented injector was set up to measure fuel pressure inside the feed line of the injector and the lift of the control piston. Different nozzles showed a distinguishable control piston motion depending on their different geometric specifications, which also affect the injection rates. In a second step, engine simulations were performed to investigate the impact of nozzle aging on heat release rate and engine performance of a single-cylinder…
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Investigation of an Innovative Combustion Process for High-Performance Engines and Its Impact on Emissions

FKFS-Marco Chiodi, Andreas Kaechele
FKFS / IVK, University Stuttgart-Michael Bargende
Published 2019-01-15 by SAE International in United States
Over the past years, the question as to what may be the powertrain of the future has become ever more apparent. Aiming to improve upon a given technology, the internal combustion engine still offers a number of development paths in order to maintain its position in public and private mobility. In this study, an innovative combustion process is investigated with the goal to further approximate the ideal Otto cycle. Thus far, similar approaches such as Homogeneous Charge Compression Ignition (HCCI) shared the same objective yet were unable to be operated under high load conditions. Highly increased control efforts and excessive mechanical stress on the components are but a few examples of the drawbacks associated with HCCI. The approach employed in this work is the so-called Spark Assisted Compression Ignition (SACI) in combination with a pre-chamber spark plug, enabling short combustion durations even at high dilution levels. This operation mode leads to substantial improvements in terms of fuel consumption up to highest load conditions. Developed in close collaboration with Volkswagen Motorsport and the FKFS, the experimental…
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