Numerical Investigation of the Effect of Alcohol-Diesel Blending Fuels on the Spray-Wall Impingement Process 2016-01-1276
Impingement of spray against the cylinder wall or piston bowl is an unavoidable physical process in homogeneous charge compression ignition (HCCI) and premixed charge compression ignition (PCCI) engines using early injection strategy. It directly affects fuel-air mixture formation, combustion and exhaust emission. In addition, the alcohol fuels such as methanol, ethanol and n-butanol are regarded as hopeful alternative fuels as well as fuel additive for HCCI and PCCI diesel engines to improve the emission level. The better understanding for the effect of alcohol-diesel blending fuel on the spray-wall impingement process is helpful for the improvement of HCCI and PCCI diesel engines.
In this paper, the effects of three different alcohol-diesel blending fuels (methanol, ethanol and n-butanol) on the spray-wall impingement process were studied. Numerical investigation was performed in AVL FIRE code. The predicted equivalence ratio and droplet distribution in the spray-wall impingement region were discussed. The spray-wall impingement region was divided into three regions which were the main wall-jet region, the stagnation region, and the downstream region. The history of calculated droplet tangential velocity in each region was analyzed. Besides, overall Sauter mean diameter (SMD) and local SMD of the impinged spray at different heights were also compared.
Conclusions drawn from the simulation results suggested that methanol-diesel blending fuel with high substitution ratio could obtain more homogenous near-wall mixture and smaller local/overall SMD. The ratio of spray-wall impingement of the methanol-diesel blending fuel was smaller than the other two alcohol-diesel blending fuels due to the lower boiling point, smaller droplet SMD and higher droplet reverse velocity. In addition, droplet tangential velocity distribution of the different alcohol-diesel blending fuels was influenced by the combined effect of density, viscosity and surface tension. For droplet overall and local SMD, the effect of the boiling point should be considered.