Supercritical droplet vaporization and combustion studies

Givler, Shawn; Abraham, John

doi:10.1016/0360-1285(95)00013-5

Cited by 145 publications

(58 citation statements)

References 51 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Transient characteristics of liquid-and gas-phases, the non-ideal behavior of the gas-phase, the real gas effects on the heat of vaporization and on the vapor-liquid equilibrium conditions at the droplet interface, and the solubility of the ambient inert species into the liquid droplet, become important at high pressure and high temperature environments. Studies on droplet evaporation at high pressures have been reported by several authors [1][2][3]. Several investigators [4][5][6][7][8][9][10][11][12], have addressed the problem of gas solubility in their research works on high pressure droplet vaporization.…”

Section: Introductionmentioning

confidence: 99%

“…Several investigators [4][5][6][7][8][9][10][11][12], have addressed the problem of gas solubility in their research works on high pressure droplet vaporization. Nomura et al [13] have measured experimentally the temporal variation of (d / d 0 ) 2 for an n-heptane droplet at different ambient pressures and temperatures under microgravity conditions. Several investigators have reported about the transition from subcritical to supercritical vaporization regime and several others have studied the characteristics of droplet gasification at supercritical conditions [14][15][16][17][18][19][20][21][22][23][24][25].…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Subcritical and supercritical droplet evaporation within a zero-gravity environment: Low Weber number relative motion

Zhang

Raghavan

Gogos

2008

International Communications in Heat and Mass Transfer

View full text Add to dashboard Cite

A validated comprehensive axisymmetric numerical model, which includes the high pressure transient effects, variable thermo-physical properties and inert species solubility in the liquid phase, has been employed to study the evaporation of moving n-heptane droplets within a zero-gravity nitrogen environment, for a wide range of ambient pressures and initial freestream velocities. At the high ambient temperature considered (1000 K), the evaporation constant increases with the ambient pressure. At low ambient pressure, the evaporation constant becomes almost a constant during the end of the lifetime. At high ambient pressures, the transient behavior is present throughout the droplet lifetime. The final penetration distance of a moving droplet decreases exponentially with increasing ambient pressure. The average evaporation constant increases with ambient pressure. The variation is almost linear for reduced ambient pressures smaller than approximately 2. For higher values, depending on the initial freestream velocity, the average evaporation constant either becomes a constant (at low initial freestream velocities) or it non-linearly increases (at high initial freestream velocities) with the ambient pressure. Droplet lifetime decreases with increasing ambient pressure and/or increasing initial freestream velocity.

show abstract

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Subcritical and supercritical droplet evaporation within a zero-gravity environment: Low Weber number relative motion

Zhang

Raghavan

Gogos

2008

International Communications in Heat and Mass Transfer

View full text Add to dashboard Cite

show abstract

“…Above T r of 2, gasification lifetime drops sharply with pressure, see Giveler and Abraham [6], to a minimum at about P r of 5, ■ J)see Umemura [5], and rises again due to lowered mass diffusivity at high pressures. Initial decline in gasification time with pressure is primarily due to reduced enthalpy of vaporization but later when it vanishes, low mass diffusivities slow down the gasification process.…”

Section: Introductionmentioning

confidence: 99%

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

Chehroudi¹,

Talley²,

Coy³

1998

View full text Add to dashboard Cite

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! 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...

show abstract

“…As such, this process was called diffusive mixing. It can be noted that a number of publications have been referring to this process as supercritical evaporation [13,14], but diffusive mixing appears to be more descriptive of such process.…”

Section: Resultsmentioning

confidence: 99%

Transcritical mixing of sprays for multi-component fuel mixtures

Manin

Crua

Pickett

2017

Proceedings ILASS–Europe 2017. 28th Conference on Liquid Atomization and Spray Systems

View full text Add to dashboard Cite

The mixing of fuels with oxidizer has been an increasingly interesting area of research with new engine technologies and the need to reduce emissions, while leveraging efficiency. High-efficiency combustion systems such as diesel engines rely on elevated chamber pressures to maximize power density, producing higher output. In such systems, the fuel is injected under liquid state in a chamber filled with pressurized air at high temperatures. Theoretical calculations on the thermodynamics of fuel mixing processes under these conditions suggest that the injected liquid can undergo a transcritical change of state. Our previous experimental efforts in that regard showed through highspeed imaging that spray droplets transition to fluid parcels mixing without notable surface tension forces, supporting a transcritical process. Only mono-component fuels were used in these studies to provide full control over boundary conditions, which prevented extrapolation of the findings to real systems in which multi-component fuels are injected. Multi-component fuels add another layer of complexity, especially when detailed experiments serve model development, requiring the fuels to be well characterized. In this work, we performed high-speed microscopy in the near-field of high-pressure sprays injected into elevated temperature and pressure environments. A reference diesel fuel and several multi-component surrogates were studied and compared to single component fuels. The results support that a transition occurs under certain thermodynamic conditions for all fuels. As anticipated, the transition from classical evaporation to diffusive mixing is affected by ambient conditions, fuel properties, droplet size and velocity, as well as time scales. Analogous to previous observations made with the normal alkane sprays, the behavior of the multi-component fuels correlate well with their bulk critical properties. KeywordsDiesel sprays, Transcritical mixing, Multi-component fuels. IntroductionDespite the growth of alternative technologies for power generation in transportations systems, these technologies only represent a fraction of the worldwide vehicle fleet. Forecasts predict that thermal engines are still going to be highly dominant in decades to come [1]. The same predictions expect a 75 % increase in fuel demand between air, marine and rail transportation, while heavy-duty alone would account for 40 % of the total transportation energy demand. Even with the substantial improvements in gasoline direct-injection and the development of promising new combustion strategies (e.g., homogeneous-charge compression-ignition, spray-guided spark ignition or gasoline compression-ignition), heavy-duty, marine and rail transportation are expected to rely on diesel combustion for years to come. The mixing process between the injected fuel and the oxidizer in diesel engines has been long identified as a key parameter to efficient and clean combustion. Experiments have been devoted to understanding mixing under such conditions, but gaps remain ...

show abstract

Supercritical droplet vaporization and combustion studies

Cited by 145 publications

References 51 publications

Subcritical and supercritical droplet evaporation within a zero-gravity environment: Low Weber number relative motion

Subcritical and supercritical droplet evaporation within a zero-gravity environment: Low Weber number relative motion

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

Transcritical mixing of sprays for multi-component fuel mixtures

Contact Info

Product

Resources

About