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To improve today’s 1D engine simulation techniques it is important to investigate how well complex geometries such as the manifold are modeled by these engine simulation tools and to identify the inaccuracies that can be attributed to the 1D assumption. Time resolved 1D and 3D calculations have been performed on the turbulent flow through the outer runners of an exhaust manifold of a 2 liter turbocharged SI engine passenger car The total pressure drop over the exhaust manifold, computed with the 1D and 3D approach, showed to differ over an exhaust pulse. This is so even though a pressure loss coefficient correction has been employed in the 1D model to account for 3D flow effects. The 3D flow in the two outer runners of the manifold shows the presence of secondary flow motion downstream of the first major curvature. The axial velocity profile downstream of the first turn loses its symmetry. As the flow enters the second curvature a swirling motion is formed.

It has been observed that intermittent injection leads to improved spray characteristics in terms of mixing and gas entrainment. Although some experimental work has been carried out in the past, the disintegration mechanisms that govern the breakup of intermittent jets remain unknown. In this paper we have carried out a systematic numerical analysis of the breakup of pulsated jets under different injection conditions. More specifically, the duty cycle (share of active injection during one cycle) is varied, while the total cycle time is kept constant. The advection of the liquid phase is handled through the Volume of Fluid approach and, in order to provide an accurate, yet computationally acceptable, resolution of the turbulent structures, the implicit Large Eddy Simulation has been adopted. The results show that the primary disintegration results from a combination of stretching, collision and aerodynamic interaction effects.

In this work, the effect of swirl to tumble ratio on homogeneity, turbulence and mixing in a generic heavy duty Diesel engine during compression, is investigated using Large-Eddy Simulations. The main conclusion is that the relative importance of dilatation (relative volume change) increases whereas the effect of tumble breakdown decreases with the swirl to tumble ratio. In detail, we show that an increase in tumble raises the peak turbulence level and shifts the peak to earlier crank angles, which in turn leads to higher dissipation. Moreover, maximum turbulence level at top dead center is obtained for a combination of swirl and tumble rather than for pure tumble. Furthermore, it is observed that the peak turbulent kinetic energy displays levels three times greater than the initial kinetic energy of the tumble motion. Thus, energy is added to the flow (turbulence) by the piston through generation of vorticity by vorticity-dilatation interaction.

In this work simulation results of a round spray jet are presented using the combination of Large-Eddy Simulation (LES) and Lagrangian Particle Tracking (LPT). The simulation setup serves as a synthetic model of non-atomizing spray particles taken from the Rosin-Rammler size distribution that enter a chamber filled with gas through an inlet hole with diameter D. At the inlet gas velocity and droplet velocities are specified in addition to the initial size distribution of droplets. The Reynolds number as referred to the gas inflow velocity and jet diameter is Re=10000. The setup is advantageous for understanding the details of diesel sprays since it avoids near-nozzle spray modeling and thereof the corresponding error which is especially important in LES. Here, the implicit LES is applied so that the compressible Navier-Stokes equations are solved directly with a numerical algorithm in a fine mesh without a subgrid scale model.

Turbochargers are commonly used in automotive engines to increase the internal combustion engine performance during off design operation conditions. When used, a most wide operation range for the turbocharger is desired, which is limited on the compressor side by the choke condition and the surge phenomenon. The ported shroud technology is used to extend the operable working range of the compressor, which permits flow disturbances that block the blade passage to escape and stream back through the shroud cavity to the compressor inlet. The impact of this technology on a speed-line at near optimal operation condition and near surge operation condition is investigated. A numerical study investigating the flow-field in a centrifugal compressor of an automotive turbocharger has been performed using Large Eddy Simulation. The wheel rotation is handled by the numerically expensive sliding mesh technique. In this analysis, the full compressor geometry (360 deg) is considered.

In this paper, the performance of a radial turbine working under pulsatile flow conditions is computed with two different modeling approaches, time resolved 1-dimensional (1-D) and 3-dimensional (3-D) CFD. The 1-D modeling approach is based on measured turbine maps which are used to compute the mass flow rate and work output from the turbine for a given expansion ratio and temperature at the inlet. The map is measured under non-pulsatile flow conditions, and in the 1-D method the turbine is treated as being a quasi-stationary flow device. In the 3-D CFD approach, a Large Eddy Simulation (LES) turbulence approach is used. The objective of LES is to explicitly compute the large scales of the turbulence while modeling the effects of the unresolved scales. Three different cases are considered, where the simplest case only consist of the turbine and the most complex case consist of an exhaust manifold and the turbine.

Surge is a phenomenon that limits the operational range of the compressor at low mass flow rates. The objective of this research is to study effective operational range for a ported shroud compressor. The size of the compressor is typical for a turbocharger used on diesel engines. To be able to extend the operational range, the surge characteristics have to be assessed. This is done by performing measurement of the flow at the inlet to the compressor wheel and pressure fluctuations at the inlet and outlet of the compressor housing. Detailed numerical computations of the flow in the entire compressor section under similar operating conditions have also been carried out. The experimental work includes Particle Imaging Velocimetry (PIV) measurements of the instantaneous and mean velocity field at the inlet. At surge, low frequency pulsations are detected that seem to result from back flow already observed in stall.

In this work a comparative study between 1-D and 3-D calculations has been performed on different junctions. The geometries are a 90° T-junction with an area ratio of unity and a 45° junction with an area ratio of 1.78 between the main pipe and the side branch. The latter case had an offset between the centerlines of the main and the branched pipe. The 3-D modeling framework uses the Reynolds Averaged Navier-Stokes (RANS) equations with the k-ε model both for the steady and the unsteady flow cases. The comparison is made both under steady and pulsating flow conditions. The aim has been to assess the 1-D/3-D differences in terms of measures for flow losses. For the steady flow cases it is shown that there is a large difference between the 1-D and 3-D computed losses for both junction geometries. The differences are largest in the junction and right downstream of it.