Large Eddy Simulation of Diesel injector including cavitation effects and correlation to erosion damage

Abstract

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Application of X-ray micro-computed tomography on high-speed cavitating diesel fuel flows

“…Under these circumstances, cavitation has been found to develop inside fuel injection nozzles at the early studies of Badock et al (1999), Bergwerk (1959), Chaves et al (1995) and Nurick (1976), followed by Arcoumanis et al (2000), Blessing et al (2003), Mitroglou et al (2014) and Roth et al (2002) in more realistic real-size nozzle geometries offering optical access; equally helpful studies performed in transparent enlarged nozzle replicas [selectively (Andriotis et al 2008;Arcoumanis et al 2000;Miranda et al 2003; Mitroglou and Gavaises 2013;Powell et al 2000)] also indicate that cavitation plays an increasingly significant role in the nozzle's internal flow structure and development. Cavitation inside an injection hole is believed to enhance spray atomisation, either directly through the implosion of cavitation bubbles or indirectly because it increases turbulence in the nozzle flow (Badock et al 1999;Walther 2002); unfortunately, under certain circumstances induces erosion (Dular and Petkovšek 2015;Koukouvinis et al 2016) that may lead to catastrophic failures. Moreover, cavitation inside the injection holes promotes shot-toshot spray instabilities (Mitroglou et al 2011(Mitroglou et al , 2012Suh and Lee 2008), which, in turn, are responsible for poor combustion efficiency and increased emissions (Hayashi et al 2013).…”

Large Eddy Simulation of the Internal Injector Flow During Pilot Injection

“…The presented single bubble dynamics models do not satisfy a priori the thermodynamic equilibrium, and a finite relaxation time is required for the phase-change to happen depending on the mass transfer and time step. In the current model the mass transfer is tuned with a single parameter, similarly to [5], in order to obtain physically acceptable thermodynamic states. The bubble number density, , is then artificially increased to higher values than experimental measurements.…”

“…In [4] a density-based solver with a cavitation model based on thermodynamic equilibrium and LES assumptions was applied to the main injection of a 9-hole injector with a realistic needle-lift profile. Two different designs of an injector showing erosive cavitation were instead simulated in [5].…”

Topology and Distinct Features of Flashing Flow in an Injector Nozzle

“…The two-fluid Eulerian model has also been for the simulation of two-phase flows (Battistoni et al, 2014;Habchi 2015), since it offers generality of the solution, as the pressure and velocity fields are resolved for each phase, however it is associated with additional computational cost and increased risk of numerical instability compared to the mixture model, since a set of governing equations must be solved for each of the two phases. However, the use of the mixture model has been proven adequate for predicting cavitating/flashing flows Schmidt et al, 2010), even high-velocity compressible flows within complex geometrical layouts (Koukouvinis et al, 2016). Hence, the use of a single-fluid model is justified in replicating a twophase distribution by a density ratio, provided that the grid resolution is fine enough.…”