Atomization and Sprays

EFFECT OF ETHANOL AND AMBIENT PRESSURE ON PORT-FUEL-INJECTION SPRAYS IN AN OPTICALLY ACCESSIBLE INTAKE CHAMBER

RESUMO

Ethanol-blended gasoline fuels are penetrating the market due to the renewable nature of ethanol and an anti-knock benefit associated with ethanol's higher octane number. Although ethanol usage is already popular in gasoline engines using port fuel injection (PFI), little fundamental information is available regarding important spray parameters. To address this issue, PFI sprays were studied in an optical chamber simulating boosted intake conditions. Using a high-resolution CCD camera, Mie-scattered spray images were obtained and processed to determine spray-tip penetration, mean droplet diameter, and number of droplets. The ethanol-to-gasoline ratio was varied to investigate the effect of ethanol blending on these spray parameters. Mie-scattering imaging was also performed for various intake pressures considering turbocharged or supercharged conditions. From the experiments, expected trends were observed such as increasing tip penetration and decreasing mean droplet diameter with increasing time after the start of injection. Evidence of droplet breakup and evaporation during the spray penetration was also identified from detailed analysis of mean droplet diameters and number of droplets. Unexpected trends were also observed from ethanol sprays. Despite its lower vapor pressure, higher boiling point, and higher heat of vaporization, ethanol sprays showed a lower tip penetration and smaller droplet size than gasoline. The multicomponent nature of conventional gasoline was used to explain this trend: Heavy molecules of gasoline break up and evaporate at a slower rate than ethanol. It was also found that increased ambient pressure caused a shorter spray-tip penetration due to higher ambient drag. By contrast, the mean droplet diameter was larger for higher ambient pressure because of decreased evaporation rate associated with increased saturation temperature. The fundamental information obtained in this study will help develop commercially viable ethanol-fueled engines without compromising high-power performance.