Effervescent atomization of gasoline containing dissolved CO₂

An experimental study of the steady-state atomization process of gasoline containing dissolved CO₂, is presented. A fuel injection system has been designed to produce a spray having a lower Sauter mean diameter (SMD) than that obtained typically with a direct fuel injection system for the same injection pressure. The downstream part of the injector consists of an inlet orifice, an expansion chamber, a swirl duct, and a discharge orifice. When the mixture enters the expansion chamber, apart of the dissolved gas is transformed into tiny bubbles that grow inside the expansion chamber. When the mixture is driven out through the discharge orifice, these bubbles undergo a rapid flashing process, resulting in a rapid disintegration of the liquid bulk into small droplets. In the present work, we investigate experimentally the effect of the design parameters (geometric proportions, injection pressure, and CO₂ content) on the spray characteristics. The spray characteristics (SMD and D₉₀) were measured with a laser particle size analyzer (Malvern X-Mastersizer), and a digital camera was employed to record the spray angle. An overall analysis has been performed to evaluate the advantage of the proposed method over its counterparts, in terms of the total energy required to produce a desired spray. It is concluded that the atomization of gasoline fuel containing dissolved CO₂ is significantly promoted by the flash-boiling phenomenon and results in low-SMD and-D₉₀ sprays. It was also found that the spray structure of a fuel/dissolved gas mixture is essentially different from that of a single-component fuel.