Bernhard Geringer

Limits on downsizing in spark ignition engines due to pre-ignition

The combination of gasoline direct injection and supercharging technologies allows the substitution of naturally aspirated engines through downsized supercharged engines with comparable performance. However, increasing the mean effective pressure is limited by the occurrence of unwanted pre-ignition phenomena. The following article provides an insight into the pre-ignition phenomenon and its relevant triggering mechanisms. The presented results stem from a research project by Volkswagen AG Group Research, in cooperation with the Institute for Internal Combustion Engines and Automotive Engineering at Vienna University of Technology.

A Detailed Analysis of the Initiation of Abnormal Combustion with Reaction Kinetics and Multi-cycle Simulation

For highly boosted gasoline engines with direct injection (DI) the operating conditions with lowest fuel consumption are restricted by irregular combustion like knocking. Therefore, the initiation mechanism for knocking was the subject of this research work. A 4-cylinder DI test engine that was provided by GM Europe was set up at the institute’s test bench. Experimental data at low speed at the knock limit (2–3 knock events per 100 cycles) were the basis for numerical investigations. A 1D multi-cycle simulation of gas-exchange and combustion was applied to calculate the in-cylinder properties and charge composition for the knocking cycles. Additionally, a CFD-simulation was carried out in order to obtain the spatial in cylinder distribution of temperature, mixture and residual gas. These results served to set up a stochastic reactor model including the full chemistry of the low and high temperature combustion. The model was initialised with the boundary conditions of the knocking cycle and the temperature and concentration distributions from the CFD-simulation. This method enabled the analysis of knocking combustion on the basis of chemical principles. The results of the multi-cycle analysis showed that important charge properties like the charge temperature at inlet valve closing or the internal residual gas fraction were within a narrow range over all cycles. Furthermore it could be shown that the burn duration for converting 2 % of the fuel mass correlated with cycles showing autoignition. All cycles with an accelerated early flame development showed an irregular heat release later on during the combustion phase. A detailed modelling of this behaviour was carried out for the stochastic reactor model. It could be shown that only with an initial reactor temperature distribution according to the CFD simulation, which included hot regions, the autoignition occurred as early as in the measurement. The formation of typical intermediate species for the low temperature oxidation leading to autoignition could be described. Finally, a possibility was shown to introduce quasi-spatial information of the flame propagation into the zero dimensional reactor model. In this way critical regions for knocking were identified in accordance with optical measurements of knock sources on the test bench. Most theoretical investigations on abnormal combustion are based on a simplified approach considering the mean cycle for a given operating point. However, abnormal combustion never occurred for the mean cycle but rather for a very early cycle. For that reason, this work focused especially on the detailed reconstruction of a measured knocking cycle with reaction kinetics. Considering the effect of temperature inhomogeneities and flame propagation on knock initiation in a stochastic reactor model is thereby a new and innovative approach.

Dynamic matrix control applied to emission control of a diesel engine

In this paper we suggest a hierarchical control scheme, applicable to engine control. The chosen setup facilitates the simultaneous control of emissions and torque. On the top level a standard PID controller is installed, setting the injection quantity in order to reach the demand torque, which is a prerequisite to follow a given load profile. The second level is dedicated to the emission control. We apply dynamic matrix control (DMC), which is a specific form of model predictive control. DMC stands out by a very simple way of modeling the controlled process which is represented by step responses. Constraints on the absolute values and maximum rates of change are applied to the manipulable system inputs to cope with given hardware limitations. Moreover, we incorporate so-called operational constraints, thus constraining the input variables to certain polytopic operating regions. Thereby areas with high HC emissions can be excluded in advance. Furthermore we include the predefined demand torque as input to the DMC. With the known impact of transient torque changes on the emissions, the DMC can act in an optimal way with respect to the given load profile. To cope with the nonlinearities of a combustion engine, we apply a network of several DMCs, scheduled by engine speed and load as well as by the manipulable actuators. We also propose a procedure to reduce the amount of modeling data, by introducing a parameterized formulation of the measured step responses. The proposed control concept is then evaluated on a realistic, physically-based engine model for several representative driving sequences, amongst them the well-known New European Driving Cycle (NEDC) and the highly dynamic Worldwide Harmonized Light Duty Test Cycle (WLTC). The advantages of DMC against a conventional PID control are finally summarized and demonstrated on a typical load step.

Forschungsbedarf für das Elektrofahrzeug der Zukunft

SummaryToday the requirements posted to the electric vehicle are influenced by the conventional car with combustion engine. For the electric vehicle of the first generation there is mainly a need for the suburban short-distance traffic. For this purpose the available battery technologies are at the moment usable with their attainable driving range. For the next generation of electric vehicles there is a need for higher ranges due to improved efficiency by means of reduced mass, lower rolling resistance and lower energy demands for heating and cooling. These are the goals of future research. For the vehicle itself and the electric power train the needs of research are depicted.ZusammenfassungDie heute an das Elektrofahrzeug gestellten Anforderungen sind von den klassischen Fahrzeugen mit Verbrennungsmotor geprägt. Für Elektrofahrzeuge der ersten Generation besteht insbesondere Bedarf für den suburbanen Nahverkehr. Hierfür sind die verfügbaren Batterietechnologien in ihrer damit erzielbaren Reichweite bereits einsetzbar. Für die nächste Generation sind höhere Reichweiten durch verbesserte Effizienz mittels verminderter Masse, geringerem Rollwiderstand und niedrigerem Energiebedarf für Heizung und Kühlung die Forschungs- und Entwicklungsziele der Zukunft. Für das Fahrzeug und den Antrieb wird der Forschungsbedarf dargestellt.

Optimization of Hybrid Strategies with Heuristic Algorithms to Minimize Exhaust Emissions and Fuel Consumption

The hybrid powertrain is a promising concept to contribute to achieve future CO2-targets. This paper describes a method to improve future automotive powertrains efficiently in real world driving conditions. Beside the optimization of the internal combustion engine and the electric components, the operating strategy of the hybrid powertrain is of particular importance to minimize the vehicles fuel consumption. A combination of start/stop operation, downspeeding, load-point shifting and pure electric driving can provide substantial fuel savings compared to conventional powertrains. However, in addition to the fuel consumption the more and more stringent future emission legislation must be taken into the account when optimizing the operating strategy. A fast light-off of the catalytic converters and a control of the converter temperatures during pure electric driving must be achieved. Therefore, numerous parameters have to be optimized simultaneously to realize the best solution for the hybrid powertrain. A numerical optimization approach was used to define the operating strategies efficiently for the mentioned goals. The results of this optimization were compared to the fuel consumption and the exhaust emissions of the conventional powertrain. The potential of a further strategy optimisation could be evaluated. Generally, it could be shown that long phases of electric driving combined with aggressive load point shifting to balance the battery’s state of charge are most favorable in terms of efficiency. The phases of electric driving are additionally limited by the temperature drop of the catalysts and the lack of pollutant conversion after restart. This is a new and innovative approach to develop electrified powertrains efficiently. Finally it can be stated, that the numerical optimization method proved to be a powerful tool to support the development process of hybrid powertrains with numerous degrees of freedom.

On-Board Powerplant Numerical Optimization of Internal Combustion Engines in Series Hybrid-Powertrains

Serial-hybrid-powertrains in extended-range electric vehicles (E-REV) pose different requirements to internal combustion engines (ICE) than conventional vehicles. In E-REVs ICEs are not used for propulsion but for battery charging and cabin heating. This work deals with the design of ICEs in serial-hybrid-powertrains. It considers different operating strategies as well as the dimensioning of the electric components of the powertrain and the thermal management. Therefore, a longitudinal dynamic model was developed using GT-SUITE including the ICE and the thermal management. The engine was operated on a test bench in parallel to create the necessary maps for the numerical investigations. Due to the high amount of parameters that can be optimized when determining the operating strategies and dimensioning the components, by a numerical optimization method that was developed and customized for this problem. The numerical investigations showed that for higher vehicle speeds the direct propulsion of the ICE is more efficient while for lower speeds the operation of the ICE as a generator is the more efficient strategy. Additionally, the influence of the ambient temperature on the efficiency was taken into account. At low ambient temperatures it is necessary to heat up the driver’s cabin electrically. Using a thermal numerical model it was possible to show the dependency on the energy consumption, the component dimensioning and the configuration of the operation strategies. The most favourable powertrain setup and the most efficient operating strategies were achieved by using the described numerical optimization method. The new and comprehensive approach was to consider the entire vehicle including mechanical components, thermal components and operating strategies in the numerical model setup and the holistic optimization of them using self-developed numerical optimization software.

Evaluation of the residual gas tolerance of homogeneous combustion processes with high exhaust-gas recirculation rates

The development of concepts with low emissions and fuel consumption for gasoline engines requires an early knowledge of the combustion process’ residual gas tolerance. At the Institute for Internal Combustion Engines and Automotive Engineering at Vienna University of Technology a method was developed that allows the dimensioning of this significant parameter based on CFD simulation. For that reason two engines were investigated experimentally at the engine test bench as well as with CFD simulation methods to create an increased charge motion.

Using fuel figures to evaluate pre-ignition in gasoline engines

Due to the increasing power density of modern downsized gasoline engines, they sporadically exhibit combustion anomalies, known as pre-ignition, particularly in the low-end torque region. In addition to the variety of causes of pre-ignition the fuel plays an essential role in this regard. As part of a cooperative FVV project, two experimental methods have been developed at the Vienna University of Technology and the RWTH Aachen University, which evaluate the pre-ignition resistance of a fuel due to thermodynamically critical conditions in the gas phase.

Kraftstoffkennzahlen zur Beschreibung von Vorentflammung in Ottomotoren

Moderne Downsizing-Ottomotoren zeigen aufgrund der zunehmenden Leistungsdichte der Aggregate speziell im unteren Drehmomentbereich sporadisch auftretende Verbrennungsanomalien, sogenannte Vorentflammungen. Neben einer Vielzahl an innerbeziehungsweise außermotorischen Ursachen der Vorentflammung spielt der Kraftstoff in diesem Zusammenhang eine wesentliche Rolle. An der TU Wien und der RWTH Aachen wurden im Zuge eines kooperativen FVV-Vorhabens zwei experimentelle Methoden entwickelt, welche die Vorentflammungsresistenz eines Kraftstoffs infolge thermodynamisch kritischer Bedingungen in der Gasphase bewerten.

Elektromobilität – Chancen für die österreichische Wirtschaft

SummaryGradual electrification of the drive propulsion system and the associated new technologies for vehicle and infrastructure will lead to changes in the classic car industry as well as other industry sectors. In the course of these changes not only technological issues arise, but also questions about the impacts of new drive concepts on the Austrian economy and the industrial location. In order to analyze the impacts, the Federal Ministry of Economy, Family and Youth, the Austrian Economic Chambers and the Federation of Austrian Industries commissioned the Institute for Powertrains and Automotive Technology of the Vienna University of Technology and Fraunhofer Austria Research GmbH to conduct a study. Potentials for the establishment and development of value added and employment effects have been identified within detailed analyses of the strengths and weaknesses of the Austrian economy. The study identifies direct value added effects in the amount of € 300 million and 3800 full-time employees in 2020 and approximately € 1.2 billion and 14,800 full-time workers in 2030. Taking induced effects, the overall effects of electric mobility are estimated at a value added of € 2.9 billion and 35,600 full-time workers. The Austrian potentials used best in terms of expertise and market position even a potential in the amount of 57,100 full time employees will result for the year 2030.ZusammenfassungDie schrittweise Elektrifizierung des Antriebs und die damit verbundenen neuen Technologien für Fahrzeug und Infrastruktur werden zu Veränderungen im klassischen Automobilbereich und anderen Wirtschaftsbereichen führen. Im Zuge dieser Veränderungen geht es aber nicht immer nur um technologische Fragen, sondern auch um Fragestellungen hinsichtlich der Auswirkungen neuer Antriebskonzepte auf die österreichische Wirtschaft und den Industriestandort Österreich. Um diese Auswirkungen zu analysieren, wurde von Wirtschaftsministerium, Wirtschaftskammer Österreich und Industriellenvereinigung eine Studie beim Institut für Fahrzeugantriebe und Automobiltechnik der TU Wien und der Fraunhofer Austria Research GmbH in Auftrag gegeben. Über detaillierte Analysen der Stärken und Schwächen der österreichischen Wirtschaft wurden Potenziale zum Auf- und Ausbau der Wertschöpfung und Beschäftigung identifiziert. Die direkten Potenziale der Elektromobilität liegen bei einer Wertschöpfung in Höhe von 300 Mio. € und einer Beschäftigung von 3.800 Vollzeitbeschäftigten im Jahr 2020 und ca. 1,2 Mrd. € und 14.800 Vollzeitbeschäftigten in 2030. Unter Berücksichtigung induzierter Effekte wird die Gesamtwirkung der Elektromobilität auf eine Wertschöpfung von 2,9 Mrd. € und 35.600 Vollzeitbeschäftigte geschätzt. Werden die Potenziale Österreichs im Hinblick auf Kompetenz und Marktstellung bestmöglich genutzt, dann resultiert sogar ein Gesamtpotenzial von 57.100 Vollzeitbeschäftigen im Jahr 2030.