George Strotos

EVAPORATION OF A SUSPENDED MULTICOMPONENT DROPLET UNDER CONVECTIVE CONDITIONS

Computational fluid dynamics results of an evaporating suspended multi-component liquid fuel droplet are presented. The droplet consists of n-heptane, n-decane or a mixture of the two and it is held in suspension at the end of a thin diameter pipe. The droplet is exposed to a uniform air flow having temperature higher than that of the droplet. The Navier-Stokes equations are numerically solved together with the VOF methodology employed for tracking the liquid-gas interface using an adaptive local grid refinement methodology. The vapour concentration of each component within the air is calculated from its corresponding transport concentration equation. The droplet temperature and its evaporation rate are predicted as function of time using a local evaporation model applicable to cases where the droplet’s shape deviates from the spherical one. The numerical results are compared against experimental data available in the literature. The ‘final’ equilibrium position of the suspended droplet is predicted as well as the internal liquid circulation which results to the entrapment of the more volatile species inside the droplet centre.

Numerical investigation of the aerodynamic breakup of diesel droplets under various gas pressures

Financial support from the MSCA-ITN-ETN of the European Union’s H2020 programme, under REA grant agreement n. 675676 is acknowledged.

Evaluation of friction heating in cavitating high pressure Diesel injector nozzles

Variation of fuel properties occurring during extreme fuel pressurisation in Diesel fuel injectors relative to those under atmospheric pressure and room temperature conditions may affect significantly fuel delivery, fuel injection temperature, injector durability and thus engine performance. Indicative results of flow simulations during the full injection event of a Diesel injector are presented. In addition to the Navier-Stokes equations, the enthalpy conservation equation is considered for predicting the fuel temperature. Cavitation is simulated using an Eulerian-Lagrangian cavitation model fully coupled with the flow equations. Compressible bubble dynamics based on the R-P equation also consider thermal effects. Variable fuel properties function of the local pressure and temperature are taken from literature and correspond to a reference so-called summer Diesel fuel. Fuel pressurisation up to 3000bar pressure is considered while various wall temperature boundary conditions are tested in order to compare their effect relative to those of the fuel heating caused during the depressurisation of the fuel as it passes through the injection orifices. The results indicate formation of strong temperature gradients inside the fuel injector while heating resulting from the extreme friction may result to local temperatures above the fuels boiling point. Predictions indicate bulk fuel temperature increase of more than 100°C during the opening phase of the needle valve. Overall, it is concluded that such effects are significant for the injector performance and should be considered in relevant simulation tools.

Role of heat transfer in bubble dynamics neglecting phase change. A numerical study

Financial support from the MSCA-ITN-ETN of the European Union’s H2020 programme, under REA grant agreement n. 675676 is acknowledged.