Browse Publications Technical Papers 2004-01-1840
2004-06-08

Numerical Simulation of the Evolution of the Soot Particle Size Distribution in a DI Diesel Engine Using an Emulsified Fuel of Diesel-Water 2004-01-1840

Soot formation in DI diesel engines is caused by the in-homogeneous mixture of evaporated diesel fuel and air. Locally fuel-rich regions are the origin of soot formation. Even though the higher temperatures during the combustion process assist the oxidation process, the formation of NOx pollutants increases with increasing temperature, which is known as soot-NOx trade-off. One measure to reduce both soot and NOx emissions uses an emulsified fuel where the fuel is replaced by an emulsion of diesel-water in order to homogenise the mixture formation process.
The influence of such an emulsion on the pollutant formation was numerically examined using the CFD code KIVA-3V for the flow and the Representative Interactive Flamelet model (RIF) for the combustion modelling and combustion turbulence interaction respectively. The diesel fuel was replaced by a surrogate fuel consisting of 70% n-decane and 30% α-methylnaphthalene. For this model fuel, a detailed reaction mechanism with 118 chemical species and 506 elementary reactions including sub-mechanisms for NOx and soot was used.
The results of the simulation are in a good agreement with the experimental data. The higher momentum of the injected emulsion and the higher latent heat of water lead to a better mixture formation process and reduced maximum temperatures. Therefore, less soot and less NOx can be found in the exhaust gas.
Since the equations of the first two moments of the particle size distribution are solved by the RIF-code, only the global quantities number density and soot concentration can be computed. Indeed, it is preferable to analyse the evolution of the particle size distribution. This was achieved by using the software package PREDICI [1] as a post-processing step. The evolution of the particle size distribution function shows that due to the injection of an emulsion of 49% water, by mass, the distribution function is broadened and its number size density is 60% less than compared to the injection of pure diesel.

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