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This thesis summarizes the author’s developments of combustion models and multi-objective optimization methods for gasoline and diesel engines. The combustion models belong to the family of zero-dimensional stochastic reactor models introduced in the 1990s to improve the prediction of emissions with detailed chemistry in partially stirred reactors.
The first part introduces the fundamentals of the physical and chemical models describing the combustion process. As a novelty, k−ε turbulence models were implemented in the stochastic reactor model to predict the turbulent time and length scales in gasoline and diesel engines. This development allowed an improvement of the models for convective heat transfer, fuel evaporation, gas exchange across the valves, turbulent flame propagation and crevice flow, which depend on the turbulent time and length scales.
In the second part, the multi-objective optimization platform for automatic training of the stochastic reactor model is presented. The optimization method considers multiple operating points to find a set of model parameters that predict performance and emissions over the entire engine map. The Non-domination Sorting Genetic Algorithm II is combined with the stochastic reactor model and response surface models to find the best Pareto front. Multi-criteria decision making is used to select the best designs from the Pareto front.
Finally, the third part of this thesis deals with the validation of the stochastic reactor model and the multi-objective optimization platform. For this purpose, experiments of two single-cylinder research engines with spark ignition, one passenger car engine with compression ignition and one heavy duty engine with compression ignition are used. For the spark ignition engines, a set of model parameters was found that predicts well the power and emissions over the whole engine map. The calculated turbulent kinetic energy, dissipation, and angular momentum follow the trends of the three-dimensional computational fluid dynamic simulations to a good approximation for various operating points. For the two compression ignition engines, the prediction of combustion progress and nitrogen oxide emissions are in good agreement with the experiments. Larger discrepancies were found for the prediction of carbon monoxide and unburned hydrocarbon. Optimization of the soot model parameters improves the prediction of soot mass for operating points throughout the engine map.
Im Rahmen der vorliegenden Arbeit wird auf grundlegende Unterschiede im Brennverfahren von Benzin- und Erdgasmotoren eingegangen. Außerdem werden verschiedene Maßnahmen dargestellt, die bei einer konsequenten Auslegung des Brennverfahrens auf den Kraftstoff Erdgas zu deutlichen Wirkungsgradvorteilen führen und somit den Nachteil der geringen Speicherdichte von Erdgas (Reichweite von Erdgasfahrzeugen) verringert.
Die vorliegende Arbeit soll dem interessierten Ingenieur und Studenten des Maschinenbaus einen Überblick über die Nutzung gasförmiger Kraftstoffe für den Antrieb von Kraftfahrzeugen geben. Auf die Grundlagen der Thermodynamik und der motorischen Verbrennung wird dort näher eingegangen, wo es für das Verständnis der Zusammenhänge unabdingbar ist. Hier sei auch auf die einschlägige Literatur verwiesen. Ziel ist es zu zeigen, inwiefern sich die Brennverfahren für einen kleinvolumigen Pkw-Motor von den Großgasmotoren hinsichtlich des Nutzungsprofils unterscheiden und welche Wege zur Wirkungsgradsteigerung möglich sind.