Species Transport: Engine Manifold

What You'll Build

This lesson walks you through a CFD simulation of air–fuel mixing in an engine manifold using the Species Transport model without chemical reactions. The manifold has two inlets — one supplying air, one supplying a multi-component fuel gas — and three outlets, of which only one is open while the other two are blocked (treated as walls). The goal is to study how the species mix as they travel through the manifold and to evaluate the pressure on the blocked surfaces.

What You'll Learn

• How the Species Transport model tracks multiple gas species as they convect, diffuse, and mix — without (yet) involving combustion reactions

• How to design a 3-outlet manifold fluid domain in Design Modeler

• How to generate an unstructured mesh (~231,646 elements) in ANSYS Meshing

• How to build a multi-species mixture from the Fluent database (N₂, O₂, CO₂, CO, H₂, CH₄, H₂O)

• How to activate the energy equation and enable inlet diffusion and diffusion energy source options

• How to set species mass fractions at each inlet — air (N₂ 0.79, O₂ 0.21) and a multi-component fuel stream (CO, CH₄, CO₂, N₂, H₂)

• How to apply mass-flow inlet boundary conditions (air at 0.2335 kg/s, fuel at 0.0374 kg/s) and model blocked outlets as walls

• How to use the k-ε Standard model with enhanced wall treatment and PISO pressure–velocity coupling

• How to post-process species distributions and evaluate the outlet mixture mass flow rate (0.271 kg/s) and the pressure on the blocked outlet surfaces (771.45 Pa and 780.98 Pa)

Why It Matters

Species Transport without reactions is the foundation for mixing, intake, dilution, and ventilation analysis. Mastering multi-species mixtures and mass-fraction boundary conditions here prepares you for combustion, emissions, and any flow where gas composition matters.