Development of a one-dimensional computational fluid dynamics modeling approach to predict cycle-to-cycle variability in spark-ignition engines based on physical understanding acquired from large-eddy simulation

In order to satisfy emission standards and CO2 targets, spark-ignition engines are designed to operate with high dilution rates, compression ratios and boost levels, thus increasing the propensity for unstable combustion. Therefore it is important to address cycle-to-cycle variability (CCV) in complete engine simulators in order to support the design of viable architectures and control strategies. This work concerns the development, validation and application to a multi-cylinder spark-ignition engine of a physics-based one-dimensional combustion model able to render CCV. Its basis relies on the analysis of Large-Eddy Simulation (LES) of flow in a single-cylinder engine used to extract information relating physics to cyclic fluctuations. A one-dimensional CCV model is derived, accounting for variability related to in-cylinder aerodynamics, turbulence and mixture composition. A detailed spark-ignition model is developed, and the resulting model captures the strongly non-linear interactions between flow and combustion, starting from spark ignition and covering laminar/turbulent transition and wrinkling of the flame surface. A first validation is presented against dedicated experimental data from a single-cylinder engine. Detailed comparisons between measurements and predictions are reported on a set of parametric variations around a reference point to assess the physical bases of the model. The resulting model is applied to the simulation of the operating map of a multi-cylinder turbocharged engine. It is found able to reproduce CCV without the need to perform specific LES of that engine, highlighting a certain level of generality of the developed model.