Jens Neumann

A quasi-dimensional model of turbulence and global charge motion for spark ignition engines with fully variable valvetrains

In this article, a new in-cylinder turbulence modeling approach aims at the improvement of quasi-dimensional simulations for modern spark ignition engines with fully variable valvetrains. Within the derived quasi-dimensional turbulence model, the turbulent production term can physically react on a change of engine operation (e.g. intake valve lift, intake valve timing, engine speed and boost pressure). Moreover, the approach offers access to detailed charge motion quantities for the first time in quasi-dimensional calculations. Hence, it is able to satisfy qualitative and quantitative turbulence descriptions within the entire operating range of the engine.

A Quasi-dimensional Model of the Ignition Delay for Combustion Modeling in Spark-Ignition Engines

Quasi-dimensional (QD) modeling of combustion in spark-ignition (SI) engines allows to describe the most relevant processes of heat release. Here, a submodel for the ignition delay is introduced and applied. The start of combustion is considered from ignition to the crank angle of 5 burned gas fraction. The introduced physical approach identifies the turbulent propagation velocity of the initiated kernel by taking into account early flame expansion and geometric restrictions of the flame propagation. The model is applied to stationary operation within an entire engine map of a turbocharged direct injection SI engine with fully variable valvetrain. Based on provided cycle-averaged input data, the model delivers good results within the margins of measured cycle-to-cycle fluctuations. Thus, it contributes to the assessment of the interplay between engine, engine control unit, drivetrain, and vehicle dynamics, hence making a step toward optimization and virtual engine calibration.

Application of a Phenomenological Model for the Engine-Out Emissions of Unburned Hydrocarbons in Driving Cycles

In this work, the application of a phenomenological model to determine engine-out hydrocarbon (HC) emissions in driving cycles is presented. The calculation is coupled to a physical-based simulation environment consisting of interacting submodels of engine, vehicle, and engine control. As a novelty, this virtual calibration methodology can be applied to optimize the energy conversion inside a spark-ignited (SI) internal combustion engine at transient operation. Using detailed information about the combustion process, the main origins and formation mechanisms of unburned HCs like piston crevice, oil layer, and wall quenching are considered in the prediction, as well as the in-cylinder postoxidation. Several parameterization approaches, especially, of the oil layer mechanism are discussed. After calibrating the emission model to a steady-state engine map, the transient results are validated successfully against measurements of various driving cycles based on different calibration strategies of engine operation.

Nutzung der Ladungswechsel- und Motorprozesssimulation zur Gesamtsystembewertung von CO 2 - und Rohemissionen in Fahrzyklen

Die Verknappung fossiler Brennstoffe, steigende gesetzliche Anforderungen an das Emissionsverhalten sowie gestiegenes Umweltbewusstsein fuhren zu neuen Herausforderungen in der Entwicklung von Automobilen. Trotz der steten Verringerung des Kraftstoffverbrauchs steigen die Anspruche der Kunden in Bezug auf die bisher gewohnten Fahrleistungen, die sich im Ansprech- und Beschleunigungsverhalten des Fahrzeugs widerspiegeln. Um die Gesamtheit aller, zum Teil widerspruchlicher Anforderungen zu erfullen, gibt es verschiedene technische Ansatze, die unter anderem zu mehr Variabilitat bei den Motorstellgrosen fuhren. Auf Grund der groser werdenden Komplexitat von Verbrennungsmotoren und somit auch der Motoransteuerung und zur Kompensation der daraus steigenden Applikationskosten spielen virtuelle Methoden in der Antriebsentwicklung eine immer bedeutendere Rolle.

Aufbau einer fahrzyklusfähigen Simulationsmethodik zur Modellierung der Partikelemissionen direkteinspritzender Ottomotoren

Die Technologie der Direkteinspritzung moderner, turboaufgeladener Ottomotoren ermoglicht die Nutzung einer Reihe von effizienzsteigernden Effekten. Diese sind etwa die Erhohung des Kompressionsenddruckes durch Ladungskuhlung oder das Uberspulen ohne zusatzlichen Kraftstoffverbrauch. Durch das direkte Einbringen des Kraftstoffs in den Brennraum kann es jedoch auch zu steigenden Emissionen von Ruspartikeln kommen, die zuvor in erster Linie von Dieselmotoren bekannt waren.

A phenomenological mixture homogenization model for spark-ignition direct-injection engines

In modern turbocharged direct-injection, spark-ignition engines, proper calibration of the engine control unit is essential to handle the increasing variability of actuators. The physically based simulation of engine processes such as mixture homogenization enables a model-based calibration of the engine control unit to identify an ideal set of actuator settings, for example, for efficient combustion with reduced exhaust emissions. In this work, a zero-dimensional phenomenological model for direct-injection, spark-ignition engines is presented that allows the equivalence ratio distribution function in the combustion chamber to be calculated and its development is tracked over time. The model considers the engine geometry, mixing time, charge motion and spray–charge interaction. Accompanying three-dimensional computational fluid dynamics, simulations are performed to obtain information on homogeneity at different operating conditions and to calibrate the model. The calibrated model matches the three-dimensional computational fluid dynamics reference both for the temporal homogeneity development and for the equivalence ratio distribution at the ignition time, respectively. When the model is validated outside the calibrated operating conditions, this shows satisfying results in terms of mixture homogeneity at the time of ignition. Additionally, only a slight modification of the calibration is shown to be required when transferring the model to a comparable engine. While the model is primarily aimed at target applications such as a direct-injection, spark-ignition soot emission model, its application to other issues, such as gaseous exhaust emissions, engine knock or cyclic fluctuations, is conceivable due to its general structure. The fast calculation enables mixture inhomogeneities to be estimated during driving cycle simulations.