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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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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 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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Valve Flow Coefficients under Engine Operation Conditions: Piston Influence and Flow Pulsation

FKFS-Michael Grill
University of Stuttgart-Sven Fasse, Michael Bargende
Published 2019-09-09 by SAE International in United States
Engine valve flow coefficients are used to describe the flow throughput performance of engine valve/port designs, and to model gas exchange in 0D/1D engine simulation. Valve flow coefficients are normally determined at a stationary flow test bench, separately for intake and exhaust side, in the absence of the piston. However, engine operation differs from this setup; i. a. the piston might interact with valve flow around scavenging top dead center, and instead of steady boundary conditions, valve flow is nearly always subjected to pressure pulsations, due to pressure wave reflections within the gas exchange ports. In this work the influences of piston position and flow pulsation on valve flow coefficients are investigated for different SI engine geometries by means of 3D CFD and measurements at an enhanced flow test bench. In the past, most research work on valve flow coefficients left aside possible piston influence and, for dynamic boundary conditions, it largely omitted subtraction of the gas inertia effects, which are already covered by 1D simulation. In this work, concerning piston influence, various valve overlap…
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Valve Flow Coefficients under Engine Operation Conditions: Pressure Ratios, Pressure and Temperature Levels

FKFS-Michael Grill
University of Stuttgart-Sven Fasse, Michael Bargende
Published 2019-01-15 by SAE International in United States
Engine valve flow coefficients are not only used to characterize the performance of valve/port designs, but also for modelling gas exchange in 0D/1D engine simulation. Flow coefficients are usually estimated with small pressure ratios and at ambient air conditions. In contrast, the ranges for pressure ratio, pressure and temperature level during engine operation are much more extensive. In this work the influences of these three parameters on SI engine poppet valve flow coefficients are investigated using 3D CFD and measurements for validation. While former investigations already showed some pressure ratio dependencies by measurement, here the use of 3D CFD allows a more comprehensive analysis and a deeper understanding of the relevant effects. At first, typical ranges for the three mentioned parameters during engine operation are presented. A preliminary study for a simple nozzle geometry shows the suitability of the utilized 3D CFD code for partially overcritical flow, and demonstrates the limits of the fundamental nozzle flow equation. Steady flow simulations of two different four-stroke SI engine cylinder head geometries reveal that valve flow coefficients show…
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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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A Simulation Study of Optimal Integration of a Rankine Cycle Based Waste Heat Recovery System into the Cooling System of a Long-Haul Heavy Duty Truck

FKFS-Kangyi Yang, Michael Grill
Universitat Stuttgart-Michael Bargende
Published 2018-09-10 by SAE International in United States
As a promising solution to improve fuel efficiency of a long-haul heavy duty truck with diesel engine, organic Rankine cycle (ORC) based waste heat recovery system (WHR) by utilizing the exhaust gas from internal combustion engine has continuously drawn attention from automobile industry in recent years. The most attractive concept of ORC-based WHR system is the conversion of the thermal energy of exhaust gas recirculation (EGR) and exhaust gas from Tailpipe (EGT) to kinetic energy which is provided to the engine crankshaft. Due to a shift of the operating point of the engine by applying WHR system, the efficiency of the overall system increases and the fuel consumption reduces respectively. However, the integration of WHR system in truck is challenging by using engine cooling system as heat sink for Rankine cycle. The coolant mass flow rate influences strongly on the exhaust gas bypass which ensures a defined subcooling after condenser to avoid cavitation of pump. The coolant temperature decides the condensation pressure which impacts on the efficiency of WHR system. This paper aims to investigate…
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