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The spray characteristics of fuels when sprayed under superheated and elevated fuel pressure are markedly different than traditional fuel injection sprays. Studying fuel sprays under these conditions will help us understand the complex behaviors that may provide us with information to optimize future applications of certain technologies like supercritical spray combustion. In this work optical diagnostics are used to study the behavior of Jet A-1 under subcritical, transcritical, and supercritical sprays into open air test chambers. The experimental setup includes a high-pressure air driven pump to create the required high fuel pressure and a special heated injector to increase the temperature of the fuel inside the injector before injection to the required temperatures. Optical techniques like Schlieren and backlit shadowgraph are used to capture and study the sprays from a single hole high pressure diesel injector. A combination of 4 different temperatures and 4 different pressures are tested and the resultant images are processed to obtain quantitative measurements such as spray penetrations, spray cone angle, and spray optical density for each case. Moreover, the spray plume structure transition with changing parameters from subcritical, transcritical, and supercritical states for the fuel are also studied. The results show that with the fuel being in a transcritical state before injection there is a measurable variation in the spray cone formation and penetration for any fixed pressure. At this state the spray cone shows a bimodal spray angle distribution with increasing penetration. An increase in vapor turbulence is also observed indicating the occurrence of flash boiling of the fuel. With the fuels pushed to a supercritical state, the spray shows a thinner spray jet near the injector with a reduced overall penetration and reduced optical density near nozzle. The transition between the three different states as shown in this study gives us an interesting relationship between the spray penetration, spray cone angle and the spray optical density. This can be used as an indicator in understanding spray atomization of the fuels under supercritical spray conditions.
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A multispectral, extinction-based diagnostic for drop sizing in optically dense diesel sprays
Diesel sprays present a challenging environment for detailed quantitative measurement of the liquid field, and to date, there have been only a few efforts to characterize drop sizes within the family of Engine Combustion Network (ECN) diesel sprays. Drop sizing diagnostics, including optical microscopy and Ultra-Small Angle X-ray Scattering (USAXS), have been recently demonstrated in Spray A/D ECN activities, but little data exist to validate these results. This work therefore seeks to extend the available ECN data on the liquid phase field and provide a new comparative data set for assessment of previous ECN drop sizing measurements. In particular, this work presents the development of a two-wavelength, line-of-sight extinction measurement to examine liquid volume fraction and the corresponding droplet field in high-pressure fuel sprays. Here, extinction of lasers emitting at 10.6 μm and 0.633 μm are used for the measurement. To enable quantification of the liquid field in optically dense regions of the spray, a transfer function is developed to account for the influence of multiple scattering. The developed diagnostic is then applied to n-dodecane sprays from the ECN Spray A and Spray D injectors at varying fuel rail pressures and atmospheric chamber condition. Overall, the results show a reasonable agreement with droplet sizes measured using USAXS, as well as from more recent measurements using a Scattering-Absorption Measurement Ratio (SAMR) technique also developed in our group. This is particularly the case near the spray periphery, where on average, less than 40% difference in the measured Sauter mean diameter is observed. Nonetheless, an apparent discrepancy is observed between drop sizes from different diagnostics close to the jet centerline (i.e. nearly 100% difference between available data for Spray D injector). Moreover, the presented diagnostic shows an improved capability in the dilute regions of the spray, where x-ray-based diagnostics are generally subject to high noise and low signal sensitivity.
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- Award ID(s):
- 1653687
- PAR ID:
- 10547869
- Publisher / Repository:
- SAGE Publications
- Date Published:
- Journal Name:
- International Journal of Engine Research
- Volume:
- 21
- Issue:
- 1
- ISSN:
- 1468-0874
- Format(s):
- Medium: X Size: p. 15-25
- Size(s):
- p. 15-25
- Sponsoring Org:
- National Science Foundation
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