The Ansys Forte CFD Package is designed for internal combustion engine design applications. The modeling approach described in this Theory manual is therefore tailored to provide the most accurate solutions possible for these applications, using computing resources that are practical for every-day design activities. Ansys Forte takes advantage of well-established theoretical representations of 3-D fluid flow, spray dynamics and combustion behavior.

The dynamics of spray combustion in diesel engines are controlled by both turbulent mixing dynamics and fuel combustion kinetics. Spray dynamics and fuel vaporization are typically the dominant contributors to the creation of stratified fuel/air mixtures. Subsequently, the ignition and combustion chemical kinetics are controlled by a complex network of reactions between fuel and air species under these stratified conditions. Both spray dynamics and chemical kinetics contribute to source terms in the reacting-flow transport equations. For flame propagation in spark-ignition engine, combustion kinetics in the end-gas also controls important phenomena, such as engine knocking and emissions production. For advanced-concept engines that are based on compression-ignition strategies or dual-fuel combustion, chemical kinetics becomes even more important.

The Ansys Forte CFD Package introduces important breakthroughs in chemistry-solution techniques that greatly enhance the accuracy achievable by engine simulation within commercial design time lines. These techniques reduce simulation time by as much as two orders of magnitude when compared to conventional CFD. Chemistry models that were previously thought of as only practical for 0-D simulations now become practical for full 3-D engine simulations with moving pistons and valves. Better handling of chemistry with multi-component fuel representation makes predictive simulation possible within the schedule constraints of the concept phase of design.

For direct-injection engines, Ansys Forte also sets a new standard for accuracy in the representation of fuel-spray droplet breakup and vaporization. For example, true multi-component fuel vaporization models can now work hand-in-hand with multi-component chemistry models. In addition, new approaches to representing the gas-transport part of the spray reduce the sensitivity of the spray model to the grid. These advances together with better chemistry allow more accurate simulations at reduced computational cost, and without the intervention of expert calibration.

Ansys Forte builds on models and sub-models that have been well validated against experimental data over a broad range of conditions and over many years by engine-simulation experts. This manual describes the model assumptions and solution techniques employed. The Ansys Forte User's Guide provides end-user instructions for model inputs and for the mechanics of using the Ansys Forte Simulate user interface.