Numerical simulation of mixture homogenization through jet impingement on cylindrical obstacles

Abstract

The efficiency and cleanliness of a diesel engine is greatly improved by homogenizing the charge within the cylinder before compression combustion occurs. Homogenizing results in lower flame front temperatures and a leaner fuel–air mixture; simultaneously reducing NOx and particulate matter emissions. Experimental works have shown that high levels of dispersion and homogenization can be obtained by impinging the diesel jet onto a series of cylindrical obstacles simulating diesel spray interaction with three-dimensional highly porous structure. Each individual obstacle simulates spray interaction with wall junction of porous structure. Experiments have shown that geometrical configuration of obstacles is a key factor in optimizing multi-jet formation and spatial distribution of the charge. This paper develops computational fluid dynamics models that accurately predict the transient multi-jet formation behavior. Once validated, the numerical models have been used to generate two new five-obstacle configurations that were not tested experimentally. The models show the new configurations to have improved homogenization characteristics compared with those previously investigated and to be up to four times more space-efficient.