| 1. |
- Andersson, Mats, 1963, et al.
(författare)
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Application of laser-induced fluorescence for imaging sprays of model fuels emulating gasoline and gasoline/ethanol blends
- 2009
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Ingår i: 11th International Annual Conference on Liquid Atomization and Spray Systems 2009, ICLASS 2009. - 9781617826535
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Konferensbidrag (refereegranskat)abstract
- The performance at cold start of spark-ignited car engines is still a challenge since slow and incomplete vaporization of the fuel causes high emissions of unburned hydrocarbons and may even cause difficulties to start at very low temperatures, in particular with alternative fuels such as ethanol. One approach to improve fuel evaporation is by direct injection into the cylinder late during the compression stroke. In this study the evaporation of fuel, including selective evaporation of fuel components of different volatility, has been studied, in sprays injected into air with a controlled pressure and temperature. Planar laser-induced fluorescence (PLIF) and Mie scattering were used to image the fuel distribution in vapor and liquid phase in a cross-section of sprays. A model fuel of non-fluorescent molecules was used and a fluorescent tracer molecule was added. To simulate a fuel with a distillation curve similar to gasoline a multi-component model fuel was selected. The fuel was composed of five iso- or cyclo-alkenes with boiling points that span the 30-190°C range. As fluorescence tracers ketones: acetone, 3-pentanone and methylcyclohexanone, were used to trace light, medium-heavy and heavy fuel fractions. Besides investigating the gasoline-like model fuel, ethanol and an ethanol/multi-components fuel blend were investigated. Spray imaging was carried out in a pressurized chamber. The injector was an outward-opening piezo-actuated injector generating a hollow-cone spray. A cross-section of the spray was illuminated by laser light at a wavelength of 266 nm formed into a thin sheet. Two intensified CCD-cameras were used to detect fluorescence and scattered light. The presence and penetration of liquid was determined by detecting Mie-scattered light. The PLIF-images provided the total distribution of fuel in liquid and vapor phase, and by comparing with the Mie-images it could be determined when the vapor started to appear in areas with little or no drops present indicating the presence of fuel vapor. It was found that at 90°C the light fuel components evaporated quickly, the medium-heavy components slowly while the heavy ones remained in liquid phase. At 140°C also the medium-heavy components evaporate relatively rapidly.
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| 2. |
- Berrocal, Edouard, et al.
(författare)
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Analysis of the SLIPI technique for multiple scattering suppression in planar imaging of fuel sprays
- 2009
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Ingår i: 11th Triennial International Annual Conference on Liquid Atomization and Spray Systems. - 9781617826535
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Konferensbidrag (refereegranskat)abstract
- Structured Laser Illumination Planar Imaging (SLIPI) is a new laser sheet based diagnostic able to significantly increase the contrast of spray images by removing the multiple scattering noise contribution. The technique has been recently developed and applied to the study of a conventional hollow-cone water spray, where the transmission through the near-field spray was 26%. In such condition, it has been shown that 44% of the total optical signal, corresponding to multiply scattered photons, could be removed. In order to now employ the technique to more challenging sprays, such as air-blast atomizer and Diesel sprays, where the transmission can be reduced down to ~0.25%, further investigations and refinements of the approach are required. This article focuses on the analysis, optimization and application of SLIPI for fuel sprays by means of a modern 3-dimensional computational model. The simulation is performed via a validated Monte Carlo code in association with a ray-tracing approach, to simulate the propagation of the incident laser radiation through the spray and the collection optics respectively. This computational work aims to quantify the amount of multiple light scattering detected by both the conventional Mie laser sheet imaging and the SLIPI technique. Results are compared for two hollow-cone fuel sprays of different transmission and droplet size properties. In the first spray the laser transmission, at λ = 532 nm, is 5% in the dense region and 27% in the dilute region, with a droplet size distribution ranging from 8 to 68 µm. The second spray is assumed to be more highly atomized, with a transmission of only 0.17% in the dense region and 7.5% in the dilute region, and with a droplets size distribution ranging from 4 to 34 µm. From these numerical calculations, it is observed that the resultant SLIPI signal tends to be closer from the pure single scattering signal when reducing the spatial period of the incident modulated light. We demonstrate here that the technique should be able to suppress an unwanted light contribution up to 91%, of the light intensity detected in the conventional planar imaging.
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