Novel approach for adaptive coefficient tuning for the simulation of evaporating high-speed sprays injected into a high-temperature and high-pressure environment

Abstract

Producing reliable in-cylinder simulations for quick-turnaround engine development for industrial purposes is a challenging task for modern computational fluid dynamics, mostly because of the tuning effort required for the sub-models used in the various frameworks (the Reynolds-averaged Navier–Stokes and large eddy simulation). Tuning is required because of the need for modern engines to operate under a wider range of conditions and fuels. In this article, we suggest a novel methodology based on automated simulation parameter optimisation that is capable of delivering a priori a coefficient matrix for each operating condition. This approach produces excellent results for multiple comparison metrics like liquid and vapour penetration lengths, radial and axial mass fraction and temperature distributions. In this article, we also show for the first time that input model coefficients can potentially be linked to ambient boundary conditions in a physically consistent manner. Changes in injection pressure, charge pressure and charge density are considered. This paves the way for the tabulation of the constants in order to eliminate lengthy tuning iterations between operating conditions and move towards adaptive simulations as the piston moves changing the in-cylinder conditions. An additional discussion is performed for the validity range of existent models given that in recent years there has been a shift towards more extreme thermodynamic conditions in the injection stage (reaching the limits of transcritical flows). Although in this work the framework was implemented in the Reynolds-averaged Navier–Stokes context because this is the tool of preference of digital engineering currently by automotive industries, the approach can be easily extended in large eddy simulation.

A comprehensive investigation of RANS and LES turbulence models for diesel spray modeling via experimental diesel schlieren imaging

“…6 An excellent review of different LES modeling approaches can be found in the literature by Pope. 20 Nsikane and et al, 21 in a study published in 2019, studied the effect of different turbulence models on hightemperature diesel spray. In this study, the effect of different constants on the penetration depth of the spray was investigated.…”

Microscopic spray characteristics of ethanol and methanol blended gasoline in a direct injection spark ignition engine

“…3,4 In fact, combustion knock is a major barrier in achieving higher thermal efficiency in SI engines [1][2][3][4][5][6][7] Performance of a gasoline/ alcohol blend fuelled direct injection SI engine significantly depends on fuel spray phenomenon, therefore recently many researchers have focused on resolving this issue. [8][9][10][11][12] Also, understanding spray characteristics of both 'gasoline' and 'renewable fuels' has become very important. 13,14 Parameters that improve fuel-air mixing characteristics in internal combustion (IC) engines include spray atomization, droplet sizevelocity distribution and evaporation characteristics of the fuels.…”

Hole-to-hole variations in coupled flow and spray simulation of a double-layer multi-holes diesel nozzle

“…[21][22][23] Given the limited quantitative information around the flow structure inside diesel injectors, fuel injection equipment manufacturers require robust predictive Computational Fluid Dynamics (CFD) tools, in order to understand the physical mechanisms taking place during injection. From a physical viewpoint, modelling of such flow conditions requires the fluid compressibility 24 , mass transfer (cavitation, flash boiling, evaporation 25,26 ) and heat transfer [27][28][29] to be taken into account, which increase the complexity as well as the computational cost of the simulations. Additionally, the fluid dynamics processes occur at high Reynolds number and therefore accounting for the effect of turbulent structures and vortex dynamics, is key in explaining how the injected fuel spray is formed [30][31][32][33][34] ; this can only be resolved using very fine computational grids and scale resolving simulations, such as Large Eddy Simulation (LES), as initially presented in 35 for nozzle flows.…”