Multi-Dimensional Modeling of Ignition and Combustion in Premixed and DIS/CI (Direct Injection Spark/Compression Ignition) Engines

Tan, Z. Multi-Dimensional Modeling of Ignition and Combustion in Premixed and DIS/CI (Direct Injection Spark/Compression Ignition) Engines. University of Wisconsin-Madison, 2003.

Ignition and combustion models for SI (spark ignition), DISI (Direct Injection Spark Ignition) and diesel engines were developed and implemented in the KIVA-3V code. An equation to calculate ignition kernel growth rate was derived. The effects of the spark discharge energy and flow turbulence on the kernel growth were considered. To make it suitable for 3-D simulations, the kernel flame growth was tracked by Lagrangian Marker particles. The predicted ignition kernel size was compared with available measurement and good agreement was obtained.

Once the ignition kernel grows to a size where the turbulent flame is fully developed, a newly developed G-equation model (level set method) was used to track the mean turbulent flame propagation. When combined with a characteristic time scale combustion model, the models were also used to simulate stratified combustion in DISI engines. It was shown that by ignoring the detailed turbulent flame brush structure, fine numerical resolution is not required, thus making the models suitable for use in multidimensional modeling of engine combustion.

The ignition and combustion models were first applied to a homogeneous charge pancake geometry-combustion-chamber engine for which experimental heat flux data from probes in the engine head and cylinder liner was available. By comparing the flame arrival timings with the simulations, the models were validated. The models were also applied to a homogeneous charge Caterpillar converted propane-fueled engine. Good agreement with experimental cylinder pressures and NOx data was obtained as a function of ignition timing, engine speed and EGR levels.

To investigate the details of the triple flame structure, a ?designed? stratified mixture was introduced. It was found that the triple flame structure could be well resolved using the present combustion model. In addition, the present models were applied to simulate the ignition and combustion processes of a DISI two-stroke engine. Good agreement between the experimental data and the predictions was obtained.

The present combustion model was also successfully applied to simulate diesel combustion. It was shown that the resulting diesel combustion predictions agree very well with the conceptual model formulated by Dec [1997] from laser-based measurements.