Reza Rezaei

Phenomenological modeling of combustion and NOx emissions using detailed tabulated chemistry methods in diesel engines

Enhancing the predictive quality of engine models, while maintaining an affordable computational cost, is of great importance. In this study, a phenomenological combustion and a tabulated NOx model, focusing on efficient modeling and improvement of computational effort, is presented. The proposed approach employs physical and chemical sub-models for local processes such as injection, spray formation, ignition, combustion, and NOx formation, being based on detailed tabulated chemistry methods. The applied combustion model accounts for the turbulence-controlled as well as the chemistry-controlled combustion. The phenomenological combustion model is first assessed for passenger car application, especially with multiple pilot injections and high exhaust gas recirculation ratios for low-load operating points. The validation results are presented for representative operating conditions from a single-cylinder light-duty diesel engine and over the entire engine map of a heavy-duty diesel engine. In the second part of this study, a novel approach for accurate and very fast modeling of NO formation in combustion engines is proposed. The major focus of this study is on the development of a very fast-running NO mechanism for usage in the next generation of the engine control units. This approach is based on tabulation of a detailed chemical kinetic mechanism and is validated against the detailed chemical reaction mechanism at all engine-relevant conditions with the variation in pressure, temperature, and air–fuel ratio under stationary and ramp-type transient conditions in a perfectly stirred reactor. Using this approach, a very good match to the results from calculations with the detailed chemical mechanism is observed. Finally, the tabulated NOx kinetic model is implemented in the combustion model for in-cylinder NOx prediction and compared with the experimental engine measurement data.

Brennverfahrensauslegung an Heavy-Duty-Motoren mittels gekoppelter Hydraulik- und Verbrennungssimulation

Fur eine pradiktive Motorarbeitsprozessrechnung ist eine hohe Genauigkeit bezuglich des hydraulischen Injektorverhaltens Voraussetzung. Bei IAV wird mittels Reverse Engineering der Injektor in der 1D-Simulation detailgetreu abgebildet. Dazu werden geometrische und mechanische Kenngrosen (z.B. Federrate, Drosseldurchmesser), die bei der Einspritzung eine wichtige Rolle spielen ermittelt und in das Modell implementiert. Damit ergibt sich eine hohe Modellgute hinsichtlich Einspritzrate und - menge im gesamten Betriebsbereich des Injektors.

Control of predefined diesel combustion processes by a burn-rate model

The interaction between air-path and injection system is of great importance for the future engine control concepts. Currently, some of these interactions like reduction of the injection quantity at the smoke limit are considered. However, a physically-based consideration of the real effects of the intake air states like temperature, pressure, and composition under transient engine operating conditions should be more developed.

Neue Technologien für Aufladung – Abgasnachbehandlung – Kraftstoffe

Engine manufacturers have been increasingly pressured by legislation and economics to reduce emissions and deliver improved fuel economy. A common strategy is to downsize and downspeed engines, and then compensate for the affected transient drivability through turbocharging, transmission and axle adjustments. This strategy can be highly effective, but there is a limit to how far it can be exploited before transient boost pressure, and hence transient torque, becomes too detrimental. Turbocharger manufacturers have mitigated this transient lack of exhaust enthalpy using technologies such as VTG (variable turbine geometry) and two-stage charging, especially with EGR-equipped air systems. Parallel to this issue but not separate is the scenario that sometimes the engine has more exhaust enthalpy than what is needed to power the turbocharger compressor. As a function of driver behaviour and the type of vehicle mission, the usage typically oscillates between these two conditions – too much energy or not enough.