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In this work, diffused back-illumination extinction imaging and OH* chemiluminescence imaging were employed simultaneously to measure the soot production, spray liquid length and flame lift-off length. These experiments were conducted in a high-temperature, high-pressure constant-volume combustion chamber equipped with a common-rail fuel injector with a single 180-μm-diameter orifice. Soot formation characteristics of a blend fuel (B50) with 50% hydrogenated catalytic biodiesel (HCB) and 50% 0# fossil diesel in mass were studied. Besides, the pure 0# fossil diesel (B0) under the same operating conditions was also measured as a reference. Parametric variations of injection pressure (100 MPa, 150 MPa), ambient temperature (770 K, 820 K, 870 K) and oxygen concentration (15%, 18%, 21%) have been performed for each fuel. After analysis, it was found both liquid length and flame lift-off length of B50 are shorter than that of B0. Soot onset time of B50 appears earlier and soot initial location is closer to the nozzle than that of B0. Within the measured optical access, soot area of B50 is larger than that of B0 because of shorter lift-off length, while the difference on total soot production is less noticeable because fuel properties of B0 is more favorable for soot formation. [ABSTRACT FROM AUTHOR]

• The spray properties of liquid ammonia is studied in a constant pressure vessel at an injection pressure level up to 800 bar. • A slower initial penetratration and shorter quasi-steady liquid length of ammonia is observed compared to diesel. • Parametric trends are similar to diesel when changing ambient density, temperature, injection pressure and nozzle diameter. • 1D spray model results suggest the adequacy of mixing-controlled spray hypotheses for ammonia under non-reacting conditions. Ammonia is seen as a promising fuel to replace fossil fuels internal combustion engines, given the advantages of zero carbon emission and extensive experience in its synthesis at large scale. The ignition of ammonia in direct injection engine is still a challenge due to its unfavorable combustion characteristics, but the investigation of ammonia spray characteristics is an important step to shed light on the optimum combustion strategy. In this paper, the evolution of direct injection ammonia sprays was measured at engine-like conditions generated in a constant pressure facility by means of diffused back-illumination imaging and schlieren. In a first step, ammonia spray behavior is compared against that of Diesel fuel. Experimental results show a slower penetration of ammonia mainly due to a lagging starting penetration phase, which cannot be later recovered. In terms of liquid length, initial stages show the same pattern as for ammonia, while a shorter stabilized liquid length can be observed. Parametric trends over different operating conditions show a similar behavior to Diesel against ambient density and temperature, as well as with injection pressure and nozzle diameter. Such results, backed up by the application of a 1D spray model developed for Diesel-like fuels, suggest that ammonia sprays under non-reacting conditions have a mixing-controlled evolution. [ABSTRACT FROM AUTHOR]

Hydrogenated Catalytic Biodiesel (HCB), with excellent volatility and cetane number while without contain oxygen and aromatic hydrocarbons, have great potential to improve engine performance and emission characteristics. In this study, the effect of HCB/Diesel blended fuels properties (by mass fraction of biodiesel in diesel) on spray combustion characteristics was investigated at inert and reacting conditions in a constant volume combustion chamber. Laser (532 nm) Mie-scattering, OH∗ chemiluminescence and high-temperature luminosity were used to capture the spray liquid length, flame lift-off length and ignition delay simultaneously with the help of two intensifier charge coupled device cameras and a high speed Complementary Metal Oxide Semiconductor camera. Encouraging results were obtained at different ambient conditions (temperatures, densities, oxygen concentration) and injection pressures. The results showed that fuels with high cetane number generate shorter ignition delay, and faster auto-ignition results in a shorter flame lift-off length. A new theory was used to interpret the effect of cetane number on lift-off length. Under reacting conditions, the combustion heat release shorten spray liquid length apparently as compared with the results under inert conditions. The liquid length was slightly affected by the injection pressure and oxygen concentrations under both reacting and inert conditions, while the flame lift-off length is significantly influenced by ambient parameters and injection pressure. [ABSTRACT FROM AUTHOR]

Simultaneous imaging of OH ∗ chemiluminescence and Mie scattering of fuel spray have been performed under reacting conditions in a constant volume combustion chamber aimed for a second-generation biodiesel/diesel blended fuel. Mie scattering of 532 nm laser light technique was used for the liquid fuel measurement. In order to remove the interference signal from soot radial, filtered Mie scattered light from the fuel droplet was recorded with a charge coupled device (CCD) camera. The spray liquid length and the flame lift-off length for this high cetane-number fuel were investigated under different ambient gas conditions (temperature, density, oxygen concentration) and injection pressure. Experiments showed that the spray liquid length under the reacting condition was shorter than that under non-reacting condition. The flame lift-off length was significantly influenced by the ambient gas temperature, density, oxygen concentration and injection pressure, while the spray liquid length was slightly affected by the injection pressure and oxygen concentration. The overlap between liquid fuel and combustion flame easily happened at high temperature, high oxygen concentration, and low injection pressure conditions. [ABSTRACT FROM AUTHOR]

Methanol has been considered as a promising alternative fuel for combustion engines. However, it is quite challenging to use it directly in compressed ignition engines because of its ignition issues, especially for low load conditions. In this research, methanol was blended with hydrogenated catalytic biodiesel (HCB) using n-octanol as co-solvent. A fundamental study on spray and combustion characteristics of two ternary blends (68% HCB+17% octanol+ 15% methanol by volume; 58% HCB+17% octanol+ 25% methanol by volume) and the pure HCB was carried out within a constant volume combustion chamber equipped with a single-hole injector. As in Part Ⅰ, the spray morphology, ignition delay, and flame lift-off length have been studied in detail. This part focuses on liquid length and in-flame soot formation of reacting sprays, which were quantified utilizing a diffused back-illumination extinction imaging technique. There is an overlapping area between the fuel liquid phase and flame for all three fuels under all operating points. The reduction on liquid length after ignition is more noticeable for pure HCB than other blends, because of its shorter lift-off length. The results show that the liquid length increases with increasing fraction of methanol in the mixtures, which is mainly governed by the high latent heat of vaporization of methanol. Furthermore, extra methanol addition brings a considerable reduction on in-flame soot production because of the leaner fuel combustion at longer flame lift-off length, as well as the more oxygen content within the blends. • Methanol was blended with hydrogenated catalytic biodiesel using n-octanol as co-solvent. • The liquid length and in-flame soot of the ternary blends were measured utilizing a DBI technique. • Liquid length increases with higher methanol fraction because of its high latent heat of vaporization. • Extra methanol addition brings a considerable reduction on in-flame soot production. [ABSTRACT FROM AUTHOR]