A phenomenological mixture homogenization model for spark-ignition direct-injection engines

Abstract

In modern turbocharged direct-injection, spark-ignition engines, proper calibration of the engine control unit is essential to handle the increasing variability of actuators. The physically based simulation of engine processes such as mixture homogenization enables a model-based calibration of the engine control unit to identify an ideal set of actuator settings, for example, for efficient combustion with reduced exhaust emissions. In this work, a zero-dimensional phenomenological model for direct-injection, spark-ignition engines is presented that allows the equivalence ratio distribution function in the combustion chamber to be calculated and its development is tracked over time. The model considers the engine geometry, mixing time, charge motion and spray-charge interaction. Accompanying three-dimensional computational fluid dynamics, simulations are performed to obtain information on homogeneity at different operating conditions and to calibrate the model. The calibrated model matches the three-dimensional computational fluid dynamics reference both for the temporal homogeneity development and for the equivalence ratio distribution at the ignition time, respectively. When the model is validated outside the calibrated operating conditions, this shows satisfying results in terms of mixture homogeneity at the time of ignition. Additionally, only a slight modification of the calibration is shown to be required when transferring the model to a comparable engine. While the model is primarily aimed at target applications such as a direct-injection, spark-ignition soot emission model, its application to other issues, such as gaseous exhaust emissions, engine knock or cyclic fluctuations, is conceivable due to its general structure. The fast calculation enables mixture inhomogeneities to be estimated during driving cycle simulations.

A phenomenological modelling framework for particle emission simulation in a direct-injection gasoline engine

“…In the case of incomplete mixture formation (left colummn in Figure 1), local inhomogeneous mixture concentrations inside the combustion chamber can lead to soot-precursor formation described via virtual fuel-rich zones. Here, the model of Frommater et al 25 is incorporated which allows to transfer 3D effects into a quasi-dimensional model.…”

“…From these ideas, an empirically based model is created using information from optical measurements and 3D-CFD simulations of the injector tip area. 21,33 This model described in the following considers the film creation and the subsequent film evaporation depending on engine operation, injector geometry and deposition state (i.e. injector fouling).…”

“…32 Accompanying representative 3D-CFD simulations of the evaporation process at the injector are shown by Frommater. 33 Herein, an initially created film with an assumed film thickness has been virtually evaporated at different engine operating conditions and injector geometries by mapping a global in-cylinder CFD to a detailed CFD of the injector surrounding. It is found that velocity and injector temperature have the most significant influence.…”

Symposium for Combustion Control 2016

“…Model-based controls have proven to be a promising technology for dealing with non-linear processes. Advanced modeling techniques covering the range from reduced-order to detailed models have been presented by Frommater et al 3 and Pasternak et al 4 Real-time capability has become a key requirement for simulations utilizing Hardware-in-the-Loop environments for the calibration of electronic control units. The paper by Neumann et al 5 shows the potential of a zero-dimensional (0D) model to predict the combustion rate over a wide range of operation conditions of a modern diesel engine.…”

“…Model-based controls have proven to be a promising technology for dealing with non-linear processes. Advanced modeling techniques covering the range from reduced-order to detailed models have been presented by Frommater et al 3 and Pasternak et al 4…”