A facility was built to examine the diesel spray/combustion process. The facility centers around a constant volume vessel, which consists of a visible and infrared optically accessible cold-wall, heated-interior pressure vessel coupled to an injection system. The combustion vessel is capable of operation at 50 atm and 1000 K ͑before injection͒, was used to simulate preinjection diesel in-cylinder conditions, and was coupled to a repeatable ͑for each fuel type͒, single shot, high pressure, metering fuel injection system. A number of experimental diagnostics have been applied to the facility and will be briefly discussed and examples of typical results offered. These diagnostics include: extractive post-combustion gas concentration experiments, droplet sizing measurements, and emission/absorption temperature measurements. Results from this facility capture the critical aspects of diesel spray combustion but do not include the change in pressure associated with heat release in a small volume and volume expansion due to piston motion.
Droplet diameter and volume fraction measurements are reported as a function of radial and axial position near the injector orifice within a high-pressure spray typical of diesel systems. Injection system parameters were peak pressures of ~ 80 MPa and a single orifice injector with a 0.16 mm diameter and an L/D ratio of ~ 4. Two cases are presented and discussed in detail; injection into room ambient conditions and injection with combustion (initial conditions: 873 K, 12.5 atm). Scattered light at two infrared wavelengths was collected from a spatially resolved probe volume and, through scattering theory, both Sauter mean diameter and liquid volume fraction were produced. Spray properties were determined as a function of time at a number of points, and these points form a grid based on multiple axial and radial positions within the spray. Results from multiple, yet identical, events were used to construct twodimensional contour plots of the Sauter mean diameter and volume fraction within the spray.
We quantify the maximum error due to multiple-scattering effects for an infrared scattering droplet izing technique. Errors in Sauter mean diameters (SMDs) and liquid volume fractions were estimated lased on experimentally determined polarization properties of the scattered light. Light that is multiply scattered from spherical particles becomes randomly polarized, whereas singly scattered light from a spherical particle contains no cross-polarization scattering component. Therefore measurement of the cross-polarization component (in this case parallel) of the scattering signal is a measure of the multiply scattered light. A ratio of parallel to perpendicular polarized scattered light was experimentally determined and used to calculate an error due to multiple scattering. The infrared scattering measurements and polarization measurements used to quantify the multiple-scattering errors were applied to a typical diesel spray that was injected into three different background conditions: a room ambient condition; a room-temperature, high-pressure condition; and a combusting condition. Droplet SMD, liquid volume fraction, and multiple-scattering errors were determined for a number of locations within the spray; results indicate that the combusting case is negligibly affected by multiple scattering. However, the room ambient case exhibited notable errors due to multiple scattering near the centerline of the spray, and the high-pressure case demonstrated susceptibility to multiple scattering throughout all regions investigated. It is important to note, however, that multiple-scattering errors in many cases translate into relatively small effects on the reported droplet sizes.
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