Wall Impingement Model

Wall Impingement Model

Spray impingement on the walls occurs in many situations. For example, in internal combustion engines, gas turbines, spray painting in vehicles and ink-jet printing and also in the field of agriculture and medicine. Nowadays, the advancement in gasolines engines had led to the direct injection of gasoline into the combustion chamber, similar to direct-injection diesel engines. In gasoline direct injection engines, the fuel droplets may impact the combustion. In these engines, fuel is sprayed with pressure of up to 200 bar. At these pressures spray strikes the combustion chamber at high velocities due to short spay path. In case of port fuel injection, a large amount of fuel impinges on the walls of the intake port and the intake valve(s) [31].

In this work, drop-wall model by Naber and Reitz is considered. Three different droplet-wall models were considered. In the first and simplest called Stick, drops that reach the wall stick to the wall at the impingement location and continue to vaporize. In the second model called Reflect, drops that reach the wall rebound with their tangential

In this model the particles losses energy due to the inelastic collision with the wall. The particles rebounds of the wall with a change in momentum defined by coefficient of restitution (see figure. 5.3). Figure 5.3 Particle reflection at wall [33]

The normal coefficient of restitution defines the amount of momentum lost by the particle after collision to the before collision with the wall [33]. e_n=V_(2,n)/V_(1,n) (5.9)

Where V_n is the velocity of particle normal to the wall and subscripts 1 and 2 refer to the before and after collision. Similarly, tangential coefficient of restitution is defined tangential velocity component [33]. In the current thesis, the coefficient of restitution is considered to be 0.3.

The other models chosen to define the lagrangian spray modelling are given below in the Table