A physical-based approach for modeling cycle-to-cycle variations within a zero-dimensional/one-dimensional simulation environment

Abstract

In the spark-ignition engine development and optimization process, the cyclic variability of combustion is an essential and current issue. Cycle-to-cycle variations are extensively investigated by means of quasi-dimensional (zero-dimensional/one-dimensional) simulation modeling. To date, these model approaches have been limited either because they neglected particularly significant physical causes and factors influencing cyclic combustion variations or because of their solely empirical combustion modeling basis. However, in order to ensure the high validity of simulation results, quasi-dimensional model approaches have to accurately describe the physical background of engine combustion. Therefore, a new cyclic combustion variation model is introduced in this study. This cycle-to-cycle variation model is based on previously developed, highly sophisticated physical turbulence, ignition and combustion models, thus for the first time enabling the physical description of cycle-to-cycle variation. The model integrates the most significant physical causes of combustion variations and the factors which influence them, obtained from a literature study. Hence, the derived cycle-to-cycle variation model can physically react to changes in engine parameters such as the engine speed, load, spark timing, valve lift and timing as well as the air–fuel equivalence ratio $\lambda$ . For validation, the new cycle-to-cycle variation model is compared to a state-of-the-art cycle-to-cycle variation model and analyzed by means of engines with different combustion processes. This new cycle-to-cycle variation model uniquely features the physical background of the underlying combustion model and the integration of more influencing factors than in previous approaches. Another unique feature is its basis on extensive experimental data, gained by changing various engine parameters for homogeneous charge spark-ignition engines with different combustion/engine concepts. These include engines with high turbulence generation or a long expansion stroke via crank and valve train.