CFD Modelling of Spray formation in Diesel Engines

There’s a lot of pressure in improving the designs of internal combustion chambers. The engines of the next generation need to be light, small, powerful, and good adaptability, with the usage of less fuel and less pollution. To meet these competing requirements, innovative engine designs are drawn. The ability to analyze the performance of many engine designs has also become critical. 

A computational fluid dynamics (CFD) modeling of the spray formation process in a Diesel engine, developed in ANSYS-FLUENT using its discrete phase modeling (DPM) capability and its IC-engine module. To know about the performance of an IC engine it is important to know the fluid’s interaction and also the moving parts of the engine. 

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Spray Model:

In an engine, atomization of fuel and spray formation in the gaseous phase with liquid dispersion increases the interface between the fluids and which is necessary for heat and mass transfer. In Diesel engines, the combustion process is dependent on the spray structure of fuel interaction with air in the combustion chamber. 

Analysis: 

A 3D geometry of the engine is made using the CAD software.

This geometry is then imported to the design modeler in Ansys where the next steps are carried out. The main step is meshing and then decomposition of the geometry. After decomposition, the engines gets divided into 3 parts: 

• port, 
• chamber and 
• valve.

These regions are again divided into smaller regions to allow a fixed or moving mesh depending on the kinematics of the engine. 

The spray formation process was modeled in ANSYS-FLUENT using the dispersed phase model (DPM). This model solves the problems based on the Eulerian approach and the Lagrangian approach. 

Two-way coupling between the spray and the continuous phase is considered in the current model. With varying levels of their mutual interaction with momentum, energy, and mass exchanges. 

The initial high momentum of the spray into a chamber of high pressure leads to the breakup of the droplets by higher drag forces. 

Droplet velocities are greatest at the spray axis and decrease in the radial direction due to interaction with the entrained gas. 

In the dense spray, the probability of droplet collisions is high. These collisions can result in a change of droplet velocity and size.

Droplets can break up into smaller ones, but they can also coalesce to form larger drops. 

After setting all the parameters and checking the engine for a particular velocity and pressure we can know 

• The temperature variation inside the engine 
• Estimate the duration of the engine 
• The perfect velocity of the inlet and outlet can be set 
• Number and size of droplets. 
• Best crank angle for working 

All the parameters can vary in working for the long run and can decrease further application. 

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CFD Modelling of Spray formation in Diesel Engines