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Stuttgart Mühlhausen, Germany

Wolany A.,University of Stuttgart | Berner H.-J.,FKFS | Bargende M.,University of Stuttgart
SAE Technical Papers | Year: 2016

For scavenging the combustion chamber during the gas exchange, a temporary positive pressure gradient between the intake and the exhaust is required. On a single-scroll turbocharged four cylinder engine, the positive pressure gradient is not realized by the spatial separation of the exhaust manifold (twin-scroll), but by the use of suitable short exhaust valve opening times. In order to avoid any influence of the following firing cylinder onto the ongoing scavenging process, the valve opening time has to be shorter than 180 °CA. Such a short valve opening time has both, a strong influence on the gas exchange at the low-end torque and at the maximum engine power. This paper analyzes a phenomenon, which occurs due to short exhaust valve opening durations and late valve timings: A repeated compression of the burned cylinder charge after the bottom dead center, referred to as "recompression" in this paper. By means of a new energetic analysis (available technical work capacity) the energetic contribution of the recompression to the boost pressure generation has been examined and is presented in this paper. Furthermore two different variable exhaust valve train systems in combination with a part-scroll-separation exhaust manifold are compared in this paper. The aim is to reduce fuel consumption at the nominal power. The two exhaust valve train systems increase the valve opening duration by either a two step system or by a system with the ability to offset the valve timing. It is shown in simulation results how both systems in combination with a prolonged part-scroll-separation in the exhaust manifold reach a potential to reduce fuel consumption up to 10 %. © Copyright 2016 SAE International.

Kaal B.,University of Stuttgart | Grill M.,FKFS | Bargende M.,University of Stuttgart
SAE Technical Papers | Year: 2016

This paper presents a quasi-dimensional emission model for calculating the transient nitric oxide emissions of a diesel engine. Using conventional and high-speed measurement technology, steady-state and transient emissions of a V6 diesel engine were examined. Based on measured load steps and steady-state measurements a direct influence of the combustion chamber wall temperature on the nitric oxide emissions was found. Load steps to and from, as well as steady-state measurements down to almost stoichiometric global combustion air ratios were used to examine the behavior of nitric oxide formation under these operating conditions. An existing emission model was expanded in order to represent the direct influence of the combustion chamber wall temperature on the nitric oxide emissions as well as enabling the forecasting of nitric oxide emissions at low global combustion air ratios: Both particularly important aspects for the simulation of transient emissions. This also improves forecasting at steady-state operating points and enables forecasting for low global combustion air ratios in the first place. The improved model was validated for both steady-state and transient cases using measurements. In the area of the measured engine characteristics, an enhanced forecasting quality of the improved model was demonstrated for steady-state operating points. The simulated transient load steps delivered significantly better forecasts with the improved model. Overall, the improved model thus enables not only the prediction of nitric oxide emissions in a wider operating range, but rather also delivers more precise forecasts within the complete performance map, as well as in the case of transient operation. Copyright © 2016 SAE International.

Winke F.,FKFS | Berner H.-J.,FKFS | Bargende M.,University of Stuttgart
SAE Technical Papers | Year: 2015

This study presents a comparison of different approaches for the simulation of HEV fuel consumption. For this purpose a detailed 1D-CFD model within an HEV drivetrain is compared to a 'traditional' map-based combustion engine model as well as different types of simplified engine models which are able to reduce computing time significantly while keeping the model accuracy at a high level. First, a simplified air path model (fast running model) is coupled with a quasi dimensional, predictive combustion model. In a further step of reducing the computation time, an alternative way of modeling the in cylinder processes was evaluated, by replacing the combustion model with a mean value model. For this approach, the most important influencing factors of the 1D-CFD air path model (temperature, pressure, A/F-ratio) are used as input values into neural nets, while the corresponding outputs are in turn used as feedback for the air path model. However, while the computing speed of the simulation can be further increased, this model type loses its predictiveness, compared to detailed combustion models. The performance of said engine models is evaluated within a HEV drivetrain model. Results for the New European Driving Cycle as well as the Artemis Urban Driving Cycle are shown. © 2015 SAE International.

Seboldt D.,Robert Bosch GmbH | Lejsek D.,Robert Bosch GmbH | Wentsch M.,FKFS | Chiodi M.,FKFS | Bargende M.,University of Stuttgart
SAE Technical Papers | Year: 2016

CNG direct injection is a promising technology to promote the acceptance of natural gas engines. Among the beneficial properties of CNG, like reduced pollutants and CO2 emissions, the direct injection contributes to a higher volumetric efficiency and thus to a better driveability, one of the most limiting drawbacks of today's CNG vehicles. But such a combustion concept increases the demands on the injection system and mixture formation. Among other things it requires a much higher flow rate at low injection pressure. This can be only provided by an outward-opening nozzle due to its large cross-section. Nevertheless its hollow cone jet with a specific propagation behavior leads to an adverse fuel-air distribution especially at higher loads under scavenging conditions. This paper covers numerical and experimental analysis of CNG direct injection to understand its mixture formation. For this purpose experimental investigations were carried out by the Robert Bosch GmbH using a two-cylinder SI engine at a high load operating point with high scavenging degree. To understand the mixture phenomena the test-bench activities were supported by numerical simulations with the 3D-CFD-tool QuickSim at the FKFS. The experiments included various injection timings and valve overlaps. Additionally, the tests were performed with two different nozzle concepts (outward- and inward-opening injector) to identify the influence of the jet shape on the fuel-air distribution. The simulations also contained these parameters and particularly considered the jet development and flow field in the combustion chamber and the intake port. The test-bench investigations revealed a close dependence of the mixture formation on the injection timing and jet characteristic during scavenging operation. The associated numerical studies resulted in a good agreement with the engine performance and led to a conclusive interpretation of the observed phenomena. Copyright © 2016 SAE International.

Freuer A.,FKFS | Reuss H.-C.,FKFS
SAE International Journal of Alternative Powertrains | Year: 2013

This paper presents an autonomous cruise control for battery electric vehicles. The presented approach is based on the usage of predictive route data which is extracted out of a digital map and a wide range radar system in order to capture vehicles in front. By using the predictive route data and the information of the radar system, the autonomous cruise control can control the vehicle's speed over a wide range of driving situations without any driver interaction. The main aim of the presented autonomous cruise control is to optimize the battery electric vehicle's energy consumption. The main idea is to use predictive route data in order to calculate a consumption optimal vehicle speed trajectory by means of online optimization. The benefits of the autonomous cruise control are shown by means of real test drives and measured data evaluation. Also, this paper gives an outlook how energy consumption can be further optimized by using an automatic transmission in the battery electric vehicle in combination with a predictive gear selection strategy. Copyright © 2013 SAE International.

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