Initial growth rate and visual characteristics of a round jet into a sub- to supercritical environment of relevance to rocket, gas turbine, and diesel engines

Abstract

Public reporting burden lor this eolation of information is estimated to average 1 hour per respo-se n-udrg ~e . ~e ■-• revewng instructions, searching existing datasources gathering and maintaining the data needed, and completing and reviewing this collection of information Send ccmme-fs recarcna tr s ouroen estimate or any other aspect of this collection of information including suggestions for reducing this burden to Department of Defense. Washington Headquarters Se vices Directorate tor Info-mation AbstractThe combustion chamber temperature and pressure in many liquid rocket, gas {urbin|, and diesel engines are quite high and can reach above the critical point *¥ the injected fuels and/or oxidizers. A high pressure chamber is used to investigate and understand the nature of the interaction between the injected fluid and the environment under such conditions. Pure N 2 , He, and 0 2 fluids are injected. Several chamber media are selected including, N 2 , He, and mixtures of CO+N 2 . The effects of chamber pressure ranging from a subcritical (i.e.*elative pressure, P r = P/Pinjeoantcridca! <D to a supercritical (P r > 1) value|"at a supercritical chamber temperature (i.e.^ relative temperature T r = TAr injectam critical >1) are photographically observed and documented near the injector hole exit region using a CCD camera illuminated by a shortduration back-lit strobe light. At low subcritical chamber pressures, the jets exhibit surface irregularities that amplify downstream, lookjggintact, shiny, but wavy (sinuous) on the surface mimS evenwglly break up into irregularly-shaped small entities./^urther increase of chamber pressure causes formation of many small droplets on the surface of the jet ejecting away only within a narrow region below the critical pressure of the injected fluid similar to a second wind-induced liquid jet breakup regime. Raising the chamber pressure, transition into a full atomization regime is inhibited by rejghing near, but slightly lower than, ^"critical pressure «fthe injectant where both surface tension and heat of vaporization are sufficiently reduced. The jet appearance changes abruptly at this point and remains the same «ter resemb}£a?turbulent gas jet injection. In this region, and within the imaging resolution limitation, no droplets are seen forming and/or departing from the jet. The jet initial total divergence angle, indicating initial growth or spreading rate, is extracted from a large set of images and plotted along with ^"available data on liquid fuel injection in £ diesel engine environment, turbulent incompressible, supersonic, and variable-density jets and for incompressible but variable-density turbulent mixing layers, thus quantitatively strengthening the gas-jet like appearance. Considering this agreement, the inhibition of Tfc*-transition to atomization regime and its confirmation through the examined atomization criteria, and the visual lack of any drop; the relevancy of current injection models and some drop vaporization/combustion results under conditions where...

Injection of Fluids Into Supercritical Environments

“…Studies at DLR have also included reacting flows. Details of each facility can be found in the respective authors' previous publications, many of which are listed in the extensive references provided at the end of this paper , Chehroudi et al (1999Chehroudi et al ( -2004, Davis and Chehroudi (2004), Decker et al (1998), Mayer et al ( -2003, Oschwald et al (1999Oschwald et al ( -2002). However, adequate information regarding the facility, injector geometries, and diagnostics used is necessary in order to better understand the results presented here and to make this paper reasonably selfsufficient and complete.…”

“…Therefore, Froude number values were calculated for the AFRL facility at each condition. As an example, Chehroudi et al (1999Chehroudi et al ( , 2002 showed that for their experiments the Froude number ranges from 42,000 to 110,000. Chen and Rodi (1980) suggested that the flow is momentum dominated when a defined length scale x b is less than 0.53, while Papanicolaou and List (1988) …”

“…To some extent, and for comparable cases, disagreements in this figure can be attributed to differences in the definition of the mixing layer thicknesses and the adopted measurement methods. For detailed discussion of this figure, see Chehroudi et al (1999Chehroudi et al ( , 2002.…”

“…Chehroudi et al (1999) were the first to extract quantitative measurements of this physical parameter from the images taken of a cryogenic N 2 jet injected into GN 2 under both subcritical and supercritical pressures. These measurements led to important conclusions regarding the character of the growth rate and the behavior of the jet under such conditions.…”

High Pressure and Supercritical Combustion: Interactions of Jets with Acoustic Waves

“…Until recently, the mechanisms controlling injection and mixing under these conditions were not well understood, even to the extent that significant qualitative questions existed. However, considerable progress has been made over the past decade by research performed under this task [1][2][3][4][5][6][7][8][9][10][11][12] as well as by others [13][14][15][16][17].…”