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...

Measurements in an Acoustically Driven Coaxial Jet under Sub-, Near-, and Supercritical Conditions

“…The experimental facility, previously described by Chehroudi et al [13][14][15][16][17][18][19][20], has undergone considerable upgrades and modifications to improve the quality of the data and expand the operating range of the facility. Gaseous nitrogen (GN2) from the laboratory feed line was used to pressurize the test chamber and also to produce the jets issuing from a round coaxial injector's center post (or inner tube) and its outer annular coaxial region.…”

“…Davis et al [13,14] have assembled a single-element coaxial-jet noncombusting test rig operating at cryogenic temperatures, transcritical temperature ranges, sub-to supercritical pressures, realistic outer-to-inner-jet velocity ratios, and activation of an acoustical field inside the test chamber simulating one important aspect of the environment when combustion instability intensifies. Additional details on the development of this work can be found in previous papers by Davis et al [13][14][15] in which a coaxial jet injector was designed, based on a well-characterized single-jet injector investigated by Chehroudi et al [16][17][18][19][20].…”

“…12Plot a) dark-core length, and b) rms of variations, normalized by the inner diameter (cases[13][14][15][16][17][18][19].…”

Experimental Study of Fluid Jet Mixing at Supercritical Conditions

“…In other studies, the core length has been defined as the length up to which an appropriate threshold intensity [18] exists, or measuring the location when the standard deviation of the pixel intensity of a row is zero. Since the definition of the core length is not unique among existing studies [19,20], an algorithm has been developed here to calculate the core lengths of the jet based on the change of density along the central portion of the jet. The core length data for all three regimes were plotted against chamber-to-injectant density ratio.…”

Supercritical Pseudo-Boiling and its Relevance for Transcritical Injection

“…10 It is being replaced by studies of injection with acoustic excitation (Chehroudi and Talley, 17 Davis and Chehroudi 20,21 ) or of inert and reactive mixture behavior, such as assessments of the actual thermodynamic state of the oxygen / hydrogen mixture. While injection takes place at oxygen supercritical pressures, a local mixture might exhibit a different critical point (Yang, 58 Pfennig 46 ) with a substantially higher critical pressure.…”