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The Virtual Engine Development for Enhancing the Compression Ratio of DISI-Engines by Means of Water Injection and Variable Valve Timing

FKFS-Antonino Vacca, Francesco Cupo, Marco Chiodi, Michael Bargende
Ford Werke GmbH-Oliver Berkemeier, Maziar Khosravi
  • Technical Paper
  • 2020-37-0010
To be published on 2020-06-23 by SAE International in United States
With the aim of significantly reducing emissions, while keeping CO2 production under control, gasoline engines are faced with a new challenge to survive the constraints imposed by the RDE cycles. Current downsized engines are developed with the most recent techniques for increasing efficiency, such as high direct injection pressure, selective valve actuation, variable turbine geometry, and innovative thermal management system. The factor limiting their further step towards enhanced efficiency is the onset of abnormal combustion process. Therefore the challenge for the further boost of modern engine efficiency is the improvement of the combustion process. Different combustion technics such as HCCI and the employment of pre-chamber have been investigated, but the possibility of effectively use them in a wide range of the engine map, by fulfilling at the same time the needing of fast load control are still limiting their dissemination. For these reasons the technologies for improving the characteristics of a standard combustion process are still deeply investigated. Among these water injection in combination with either early or late intake valve closing offers the possibility…
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Potential Analysis and Virtual Development of SI Engines Operated with Synthetic Fuel DMC+

FKFS-Cornelius Wagner, Michael Grill, Mahir-Tim Keskin
FKFS / University of Stuttgart-Michael Bargende
  • Technical Paper
  • 2020-01-0342
To be published on 2020-04-14 by SAE International in United States
On the way to emission-free mobility, future fuels must be CO2 neutral. To achieve this, synthetic fuels are being developed. In order to better assess the effects of the new fuels on the engine process, simulation models are being developed that reproduce the chemical and physical properties of these fuels.In this paper, the fuel DMC+ is examined. DMC+ (a mixture of dimethyl carbonate (DMC) and methyl formate (MeFo) mainly, characterized by the lack of C-C Bonds and high oxygen content) offers advantages with regard to evaporation heat, demand of oxygen and knock resistance. Furthermore, its combustion is almost particle free. With the aid of modern 0D/1D simulation methods, an assessment of the potential of DMC+ can be made.It is shown that the simulative conversion of a state-of-the-art gasoline engine to DMC+ fuel offers advantages in terms of efficiency in many operating points even if the engine design is not altered. This is mainly due to the higher knock resistance and the lower temperatures in the intake stroke resulting from the higher amount of evaporated fuel.…
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Virtual Development of Injector Spray Targeting by Coupling 3D-CFD Simulations with Optical Investigations

FKFS-Marco Chiodi
University of Stuttgart-Antonino Vacca, Simon Hummel, Karsten Müller, Marc Reichenbacher, Michael Bargende
  • Technical Paper
  • 2020-01-1157
To be published on 2020-04-14 by SAE International in United States
Further improvements of internal combustion engines to reduce fuel consumption and to face future legislation constraints are strictly related to the study of mixture formation. The reason for that is the desire to supply the engine with homogeneous charge, towards the direction of a global stoichiometric blend in the combustion chamber. Fuel evaporation and thus mixture quality mostly depend on injector atomization features and charge motion within the cylinder. 3D-CFD simulations offer great potential to study not only injector atomization quality but also the evaporation behavior. Nevertheless coupling optical measurements and simulations for injector analysis is an open discussion because of the large number of influencing parameters and interactions affecting the fuel injection’s reproducibility. For this purpose, detailed numerical investigations are used to describe the injection phenomena. These intensive calculations are not advisable considering CFD virtual engine development. It is rather reasonable to find a methodology for a numerical characterization of the fuel injection process that takes into account both macroscopic and microscopic spray properties and to integrate these models into the complete engine simulations.…
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A Quasi-Dimensional SI Burn Rate Model for Predicting the Effects of Changing Fuel, Air-Fuel-Ratio, EGR and Water Injection

FKFS-Michael Grill
IVK, University of Stuttgart-Sebastian Hann, Michael Bargende
  • Technical Paper
  • 2020-01-0574
To be published on 2020-04-14 by SAE International in United States
As a result of the shifted R&D focus from internal combustion engines to electrified powertrains, resources for the development of internal combustion engines are restricted more and more. With that, the importance of highly efficient engine development tools is increased. In this context, 0D/1D engine simulation offers the advantage of low computational effort and fast engine model set-up. To ensure a high predictive ability of the engine simulation, a reliable combustion model is needed. Considering the increasing interest in alternative fuels, the aspect of predicting the fuel influence on combustion is of special importance. To reach these targets, the change of engine combustion characteristics with changing fuels and changing air-fuel-ratios is investigated systematically in a first step. For this purpose, engine test bed data is compared with expected fuel-dependent flame wrinkling trends based on Markstein / Lewis-number theory. Furthermore, the possibility of influences caused by the Darrieus-Landau instability is evaluated. Based on these comparisons, an existing combustion model is improved by adapting the sub-models for laminar and turbulent flame speed as well as the approach…
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A Phenomenological Homogenization Model Considering Direct Fuel Injection and EGR for SI Engines

FKFS-Michael Grill
IAV GmbH-Oliver Dingel
  • Technical Paper
  • 2020-01-0576
To be published on 2020-04-14 by SAE International in United States
As a consequence of reduced fuel consumption, direct injection gasoline engines have already prevailed against port fuel injection. However, in-cylinder fuel homogenization strongly depends on charge motion and injection strategies and can be challenging due to the reduced available time for mixture formation. An insufficient homogenization has generally a negative impact on the combustion and therefore also on efficiency and emissions. In order to reach the targets of the intensified CO2 legislation, further increase in efficiency of SI engines is essential. In this connection, 0D/1D simulation is a fundamental tool due to its applica-tion area in an early stage of development and its relatively low computational costs. Certainly, inhomogeneities are still not considered in quasi dimensional combustion models because the prediction of mixture formation is not included in the state of the art 0D/1D simulation. Therefore, a phenomenological homogenization model has been developed in this work based on 3D CFD simulations. The model is based on a finite volume approximation of the 2D convection diffusion equation rep-resenting the in-cylinder flow field. The velocity field is…
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The Isochoric Engine

University of Stuttgart-Benjamin Burger, Michael Bargende
  • Technical Paper
  • 2020-01-0796
To be published on 2020-04-14 by SAE International in United States
For the gasoline engine, the isochoric process is the ideal limit of the ideal processes. During the project, a combustion engine with real isochoric boundary conditions is built.A “resting time” of the piston for several degrees crank angle in the top dead center (TDC) can be realized with a special crank drive. This crank drive consists of two crankshafts with different strokes, which are combined. The two crankshafts rotate with a ratio of two to one in opposite directions.The total stroke corresponds to the amount of the first crankshaft, so it is possible to investigate different strokes of the second crankshaft in the same crankcase. Different “resting times” can be achieved by different strokes of the second crankshaft. A specific combination of both crankshafts make a stroke possible which corresponds to that of a conventional combustion engine.In addition to the standard cylinder pressure sensor, a quick surface temperature probe is also used as supplementary measurement technology. The influence of isochoric combustion is studied with constant air mass and constant lambda at three different strokes of…
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The Application of E-Fuel Oxymethylene Ether OME1 in a Virtual Heavy-Duty Diesel Engine for Ultra-Low Emissions

FKFS-Michael Grill
Universitat Stuttgart-Qirui Yang, Michael Bargende
  • Technical Paper
  • 2020-01-0349
To be published on 2020-04-14 by SAE International in United States
For long haul transport, diesel engine due to its low fuel consumption and low operating costs will remain dominant over a long term. In order to achieve CO2 neutrality, the use of electricity-based, synthetic fuels (e-fuels) provides a solution. Especially the group of oxymethylene ethers (OME) is given much attention because of its soot-free combustion. However, the new fuel properties and the changed combustion characteristics place new demands on engine design. Meanwhile, the use of new fuels also creates new degrees of freedom to operate diesel engines. In this work, the application of dimethoxymethane (OME1) is investigated by means of 1D simulation at three operating points in a truck diesel engine. The subsystems of fuel injection, air path and exhaust gas are sequentially adjusted for the purpose of low emissions, especially for low nitrogen oxides (NOx). Thanks to the inexistent soot-NOx trade-off, NOx can be considerably reduced by high exhaust gas recirculation (EGR) at a nearly stoichiometric operation. In addition, conceivable configurations of exhaust after-treatment system are analyzed. At last, a holistic layout of a…
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Predicting the Influence of Charge Air Temperature Reduction on Engine Efficiency, CCV and NOx-Emissions of a Large Gas Engine Using a SI Burn Rate Model

Caterpillar Energy Solutions GmbH-Stefan Palaveev, Matthias Veltman
FKFS-Sebastian Hann, Michael Grill
  • Technical Paper
  • 2020-01-0575
To be published on 2020-04-14 by SAE International in United States
In order to meet increasingly stringent exhaust emission regulations, new engine concepts need to be developed. Lean combustion systems for stationary running large gas engines can reduce raw NOx-emissions to a very low level and enable the compliance with the exhaust emission standards without using a cost-intensive SCR-aftertreatment system. Experimental investigations in the past have already confirmed that a strong reduction of the charge air temperature even below ambient conditions by using an absorption chiller can significantly reduce NOx emissions. However, test bench operation of large gas engines is costly and time-consuming. To increase the efficiency of the engine development process, the possibility to use 0D/1D engine simulation prior to test bench studies of new concepts is investigated using the example of low temperature charge air cooling. In this context, a reliable prediction of engine efficiency and NOx-emissions is important. Furthermore, restrictions to the engine operation like increase of cycle-to-cycle fluctuations due to high excess air ratio or late combustion need to be predicted as well in the engine simulation.For this purposes, a combustion model…
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Discretization and Heat Transfer Calculation of Engine Water Jackets in 1D-Simulation

FKFS-Michael Grill
University of Stuttgart-Florian Mandl, Michael Bargende
  • Technical Paper
  • 2020-01-1349
To be published on 2020-04-14 by SAE International in United States
The industry is working intensively on the precision of thermal management. By using complex thermal management strategies, it is possible to make engine heat distribution more accurate and dynamic, thereby increasing efficiency. Significant efforts are made to improve the cooling efficiency of the engine water jacket by using 3D CFD. As well, 1D simulation plays a significant role in the design and analysis of the cooling system, especially for considering transient behaviour of the engine. In this work, a practice-oriented universal method for creating a 1D water jacket model is presented. The focus is on the discretization strategy of 3D geometry and the calculation of heat transfer using Nusselt correlations. The basis and reference are 3D CFD simulations of the water jacket. Guidelines for the water jacket discretization are proposed. The heat transfer calculation in the 1D-templates is based on Nusselt-correlations (Nu = Nu(Re, Pr)), which are derived from 3D CFD simulations. Furthermore, additional modifications in the calculation routines and helpful criterions allow to handle the specific characteristics of the complex water jacket geometry user-friendly. The 1D results…
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A Method for Improvement in Data Quality of Heat Release Metrics Utilizing Dynamic Calculation of Cylinder Compression Ratio

SAE International Journal of Engines

Kistler AG, Switzerland-Mario Nahkle, David R. Rogers, Janko Meier
University of Stuttgart, Germany-Hubert Fusshoeller, Michael Bargende
  • Journal Article
  • 03-13-02-0010
Published 2019-10-29 by SAE International in United States
One of the key factors for accurate mass fraction burned and energy conversion point calculations is the accuracy of the compression ratio. The method presented in this article suggests a workflow that can be applied to determine or correct the compression ratio estimated geometrically or measured using liquid displacement. It is derived using the observation that, in a motored engine, the heat losses are symmetrical about a certain crank angle, which allows for the derivation of an expression for the clearance volume [1]. In this article, a workflow is implemented in real time, in a current production engine indicating system. The goal is to improve measurement data quality and stability for the energy conversion points calculated during measurement procedures. Experimental and simulation data is presented to highlight the benefits and improvement that can be achieved, especially at the start of combustion. The method calculated a compression ratio correction of 0.3 and 0.25 on two different gasoline engines, respectively. At 2000 rpm a deviation in the 5% and 10% energy conversion angles (CA05 and CA10) of…
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