NUMERICAL INVESTIGATION OF THE EFFECTS OF IN-CYLINDER FLOW AND MULTIPLE-INJECTION STRATEGY ON OVERALL SPRAY BEHAVIOR, EVAPORATION, AND MIXTURE FORMATION

Resumo

Using computational fluid dynamics (CFD), the effects of in-cylinder flow and injection timing were analyzed for two conditions of ethanol direct injection. The first condition consists in a unique injection during air admission, with a duration of 1.4ms, while the second condition aims to analyze the effect of splitting this injection in two injections of 0.7ms: one during air admission and another during compression. It was possible to study the spray behavior and differences between the conditions investigated, visualizing and tracking the droplets. Furthermore, it was possible to evaluate ethanol mass fraction, evaporation, mixture formation characteristics and influence of tumble and swirl on spray development during the engine cycle. Considering the cases of study, it was possible to verify the escape of fuel through admission port and poor mixture formation when the injection is made during the air admission, although fuel evaporation rate is better in this case than using two injections. It was also verified that multiple-injection can decrease the formation of fuel films, and that it is a good strategy to attain a good mixture formation and efficient combustion.