Scaling spray penetration at supersonic conditions through shockwave analysis. (15th January 2020)

• Record Type: Journal Article
• Authors: Salvador, Francisco Javier; De la Morena, Joaquín; Taghavifar, Hadi; Nemati, Arash
• Is Part Of: Fuel. Volume 260(2020)
• Publication Date: 2020-01-15
• Subjects: Diesel spray -- Shockwave -- Penetration -- Visualization; Fuel -- Periodicals; Coal -- Periodicals; Coal; Fuel; Periodicals; 662.6
• DOI: 10.1016/j.fuel.2019.116308
• Languages: English
• ISSNs: 0016-2361

Abstract

Highlights: Supersonic spray visualization is performed by injecting on sulfur hexafluoride. Normal and oblique shockwaves appear depending on the spray tip Mach reached. Supersonic penetration is higher than subsonic one at same injection conditions. Differences in penetration are due to the density gradient across the shockwave. A methodology to estimate the supersonic penetration is proposed and validated. Abstract: In the current paper, an investigation of the supersonic flow effect on shockwave generation and diesel spray penetration scaling has been performed. For this purpose, spray visualization tests have been carried out in a constant-pressure chamber at room temperature using shadowgraphy technique. Two working gases have been used: nitrogen, with similar thermodynamic characteristics to the engine environment, and sulfur hexafluoride, aimed at producing supersonic conditions at moderate injection pressure values. A total of 60 operating points, including different nozzle geometries, injection pressures and chamber densities have been studied. From the visualization study, two different kinds of shockwaves have been detected: normal or frontal, for moderate spray tip Mach (between 1 and 1.5); and oblique, when the Mach is higher than 1.5. The penetration results show that, for the same injection conditions in terms of injection pressure and chamber density, the spray propagation is equal for SF6 and N2 when the spray is on subsonic conditions, while penetration is higher for SF6 when supersonic velocity is reached. This behavior has been related to the density gradient appearing across the shockwave. A new methodology to extrapolate supersonic penetration from the well-known subsonic penetration law has been proposed, showing good agreement with the experimental results.