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Investigation of Flame Propagation Description in Quasi-Dimensional Spark Ignition Engine Modeling

Audi AG-Ulrich Baretzky, Hartmut Diel, Sebastian Wohlgemuth, Gordon Röttger
FKFS-Michael Grill
Published 2018-09-10 by SAE International in United States
The engine development process has been enhanced significantly by virtual engineering methods during the last decades. In terms of in-cylinder flow field, charge flow and combustion modelling, 3D-CFD (three dimensional) simulations enable detailed analysis and extended investigations in order to gain additional knowledge about design parameters. However, the computational time of the 3D-CFD is an obvious drawback that prevents a reasonable application for extensive analysis with varying speed, load and transient conditions. State-of-the-art 0D (zero dimensional) approaches close the gap between the demand of high computational efficiency and a satisfying accordance with experimental data. Recent improvements of phenomenological combustion approaches for gasoline spark ignition engines deal with the consideration of detailed flow parameters, the accuracy of the laminar flame speed calculation and the prediction of the knock limit. Little attention has been given to the influence of different combustion chamber designs on the prediction capability so far. This leads to an often used simplification consisting of a combustion chamber modeled as a disk and an acceptable inaccuracy of combustion modelling. With an increasing deviation of…
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Methodical Selection of Sustainable Fuels for High Performance Racing Engines

Audi AG-Stefan Dreyer, Ulrich Baretzky, Wolfgang Kotauschek, Sebastian Wohlgemuth, Florian Bach
Universitat Stuttgart-Michael Bargende
Published 2018-09-10 by SAE International in United States
As the importance of sustainability increases and dominates the powertrain development within the automotive sector, this issue has to be addressed in motorsports as well. The development of sustainable high-performance fuels defined for the use in motorsports offers technical and environmental potential with the possibility to increase the sustainability of motorsports at the same or even a better performance level. At the moment race cars are predominantly powered by fossil fuels. However due to the emerging shift regarding the focus of the regulations towards high efficient powertrains during the last years the further development of the used fuels gained in importance. Moreover during the last decades a huge variety of sustainable fuels emerged that offer a range of different characteristics and that are produced based on waste materials or carbon dioxide. This study investigates the question of which sustainable fuels offer the characteristics suitable for high-performance race engines. Equivalents to gasoline, diesel and natural gas are examined separately in order to present the options with various engine concepts. The requirements for a high-performance fuel are…
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Virtual Optimization of Race Engines Through an Extended Quasi Steady State Lap Time Simulation Approach

AUDI AG-Ulrich Baretzky, Hartmut Diel, Sebastian Wohlgemuth
FKFS-Michael Grill
Published 2018-04-03 by SAE International in United States
Minimizing the lap time for a given race track is the main target in racecar development. In order to achieve the highest possible performance of the vehicle configuration the mutual interaction at the level of assemblies and components requires a balance between the advantages and disadvantages for each design decision. Especially the major shift in the focus of racecar powerunit development to high efficiency powertrains is driving a development of lean boosted and rightsized engines. In terms of dynamic engine behavior the time delay from requested to provided torque could influence the lap time performance. Therefore, solely maximizing the full load behavior objective is insufficient to achieve minimal lap time.By means of continuous predictive virtual methods throughout the whole development process, the influence on lap time by dynamic power lags, e.g. caused by the boost system, can be recognized efficiently even in the early concept phase. As a first step, this paper presents a novel method that combines detailed 1D (one dimensional) gas dynamic engine models with the quasi steady state (QSS) lap time method.…
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Investigation of a Methane Scavenged Prechamber for Increased Efficiency of a Lean-Burn Natural Gas Engine for Automotive Applications

SAE International Journal of Engines

TU Muenchen-Laura Sophie Baumgartner, Sebastian Wohlgemuth, Sebastian Zirngibl, Georg Wachtmeister
  • Journal Article
  • 2015-01-0866
Published 2015-04-14 by SAE International in United States
Scarce resources of fossil fuels and increasingly stringent exhaust emission legislation push towards a stronger focus to alternative fuels. Natural gas is considered a promising solution for small engines and passenger cars due to its high availability and low carbon dioxide emissions. Furthermore, natural gas indicates great potential of increased engine efficiency at lean-burn operation. However, the ignition of these lean air/fuel mixtures leads to new challenges, which can be met by fuel scavenged prechambers.At the Institute of Internal Combustion Engines of the Technische Universitaet Muenchen an air cooled natural gas engine with a single cylinder displacement volume of 0.5 L is equipped with a methane scavenged prechamber for investigations of the combustion process under real engine conditions. The main combustion chamber is supplied with a lean premixed air/fuel mixture. As the excess air restrains a direct ignition by a spark plug, the prechamber must additionally be scavenged with methane to achieve nearly stoichiometric conditions and hence improve the ignition.To enhance the understanding of the processes occurring, the empirical studies are accompanied by supplementary three-dimensional…
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Piston Design Optimization for a Two-Cylinder Lean-Burn Natural Gas Engine - 3D-CFD-Simulation and Test Bed Measurements

TU Muenchen-Sebastian Wohlgemuth, Sebastian Roesler, Georg Wachtmeister
Published 2014-04-01 by SAE International in United States
The development of today's drivetrains focusses on the reduction of vehicles' CO2-emissions. Therefore, a drivetrain for urban and commuter traffic is under development at the Institute of Internal Combustion Engines. The concept is based on a lean-burn air cooled two-cylinder natural gas engine, which is combined with a hydraulic hybrid system.On the one hand, lean-burn combustion leads to low nitrogen oxides emissions and high thermal efficiency. On the other hand, there are several challenges concerning inflammability, combustion stability and combustion duration. An approach to optimize the combustion process is the design of the piston bowl.The paper presents the engine concept at first. Afterwards, a description of design parameters for pistons of natural gas engines and a technical overview of piston bowls is given. Subsequent to the analysis of the different piston bowls, a new design approach is presented. Different geometries are discussed concerning their suitability for the use in a two-cylinder natural gas engine. The piston bowls are evaluated by three dimensional computational fluid dynamics (3D-CFD) simulations. Afterwards the results of measurements at the engine…
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Turbocharging of a Two-cylinder Lean-Burn Natural Gas Engine with Uneven Firing Order

SA Charging Solutions AG-Peter Fledersbacher
TU Muenchen-Sebastian Wohlgemuth, Lisann Meiland, Georg Wachtmeister
Published 2014-04-01 by SAE International in United States
At the Institute of Internal Combustion Engines of the Technische Universitaet Muenchen a drivetrain for urban and commuter traffic is under development. The concept is based on a lean-burn air-cooled two-cylinder natural gas engine which is combined with a hydraulic hybrid system.The engine is initially mechanically charged which results in an engine speed dependent torque. Turbocharging the natural gas fuelled engine derives increased engine torque especially at low engine speeds and exploits the potential of better knock resistance of natural gas compared to gasoline fuel.The paper presents a turbocharging concept for the two-cylinder engine at first. The firing order of 180/540°CA due to the crank shaft design and the lean-burn combustion are challenging restrictions to cope with. The consequences of the uneven firing order are investigated using 1D-simulation and the matching of the exhaust gas turbocharger is shown. Afterwards, results of the engine test-bench at different engine operation points are opposed to the simulation results and evaluated. The results are compared to other approaches and assessed.Altogether, the paper describes design, application, 1D-simulation and test bench…
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Development of a Hydraulic Hybrid System for Urban Traffic

HYDAC Technology GmbH-Peter Kloft
TU Muenchen-Sebastian Wohlgemuth, Georg Wachtmeister
Published 2013-04-08 by SAE International in United States
The development of today's powertrains focuses on the reduction of CO₂ emissions. Therefore several new technologies for internal combustion engines have been established. A further tendency is the successive electrification of powertrains in hybrid vehicles. However, these trends lead to increasing system costs which are a very important aspect at the market segment of compact cars.At the Institute of Internal Combustion Engines of the Technical University of Munich a drivetrain concept for urban and commuter traffic is under development. It is based on a lean-burn air-cooled two-cylinder natural gas engine which is combined with a hydraulic hybrid system.The paper contains detailed information about the engine as well as the hybrid vehicle powertrain in parallel structure. Particular characteristics and innovations of the hydraulic hybrid system compared to systems known so far are shown. The size of the hydraulic pump is chosen in consideration of low pump losses and suitable torque in combination with the engine map. Furthermore, the paper puts emphasis on the selection of the hydraulic storage type regarding system efficiency, complexity and package. Subsequent…
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