Maximilian Brauer

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.

Effects of new nozzle hole configurations on air utilization and soot emissions of diesel engines

With conventional combustion processes there remain unused regions with air between the injection jets. To utilize these a 14-hole nozzle and a nozzle with 6 smaller and 6 larger spray hole diameters were developed. Both nozzles show strongly increased soot emissions. The optical analyses reveal improved air utilization during the main injection which leads to higher local combustion temperatures for both. The higher temperatures support the soot formation. In the later stages of the combustion the new nozzles show poorer air utilization than the references. The reference nozzles show a distinct backflow of the combustion from the piston bowl which improves the air utilization and support the soot oxidation. With the new nozzles this is less developed because of a lower spray momentum due to the smaller spray hole diameters.

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.

Konzepte zur Reduzierung der dieselmotorischen Rohemissionen – eine Bewertung im Hinblick auf Kraftstoffverbrauch und künftige RDE Anforderungen

Weltweit werden ambitionierte Ziele zur Reduktion der verkehrsbezogenen CO2-Emission verfolgt. Vor diesem Hintergrund zeigt der in Europa konstant hohe Anteil von Dieselzulassungen, aber insbesondere auch der zunehmende Anteil in den USA, welche wichtige Rolle der Dieselmotor zur Senkung des CO2-Flottenausstoses einnimmt.