Search Results

The accuracy and robustness of spray models and their implementation in current commercial CFD codes vary substantially. However, common features are that the resulting spray penetration and levels of spray-generated turbulence - two factors that strongly influence the rate of heat released during combustion - are to a great extent grid size-dependent. In the work presented here a new kind of spray model has been implemented and thoroughly tested, under various ambient conditions, in the open source code OpenFOAM. In addition, since the turbulence model applied in simulations is known to strongly affect spray penetration rates, results obtained using both the standard k-ε and RNG k-ε models have been compared. In the new spray model, designated VSB2, the traditional Lagrangian parcel has been replaced by a so-called stochastic blob containing droplets with a distribution of sizes, rather than a number of uniform-sized droplets.

Soot formation and oxidation are complex and competing processes during diesel combustion. The balance between the two processes and their history determines engine-out soot values. Besides the efforts to lower soot formation with measures to influence the flame lift-off distance for example or to use HCCI-combustion, enhancement of late soot oxidation is of equal importance for low-λ diffusion-controlled low emissions combustion with EGR. The purpose of this study is to investigate soot oxidation in a heavy duty diesel engine by statistical analysis of engine data and in-cylinder endoscopic high speed photography together with CFD simulations with a main focus on large scale in-cylinder gas motion. Results from CFD simulations using a detailed soot model were used to reveal details about the soot oxidation.