The addition of water dispersed phase into the diesel continuous phase will lead to the formation of water-in-diesel (W/D) emulsion, which significantly reduces the pollution level of NOx and particulate matters in the diesel engines. Small amount, 0.2% by volume, of surfactant material was necessary in the preparation of a stable W/D emulsion. The study of the physical and chemical properties of stable W/D emulsions is important to understand the flow behavior characteristics of these emulsions. Pure diesel fuel and three samples of W/D emulsions (10%, 20% and 30% by volume water) were examined in this study. The following properties are measured according to the corresponding ASTM standards for the pure diesel and its emulsions with 10%, 20% and 30% water: heating value, pour point, flash point, distillation data, density, viscosity, calculated cetane index, total acid number, and sulfur content. The addition of water in the emulsion caused a drop in the calorific value, final boiling point, cetane index, total acid number, and sulfur content. Increasing the water also increased the pour point, flash point, and density.
The use of elliptical jets for combustion control is an attractive passive technique due to their ability to induce flow perturbation, fluid entrainment, and jet shearing. This study presents an experimental investigation of inverse diffusion jet flames emanating from a double elliptic burner with a central circular air stream. The inner and outer streams are fed with air, while the middle one is fed with liquefied petroleum gas (LPG) as fuel. The impact of the inner-to-outer air ratio and outer elliptical tube angle on flame appearance and mean in-flame temperature was examined at a constant total air flow rate and fixed thermal input. Flame visual and thermal structures are analyzed through shadowgraph and temperature measurements in both major and minor planes of the inner elliptic fuel tube. The results reveal a dual-flame structure for all flames, with longer flames resembling normal diffusion flames as the outer air percentage increases. The outer elliptic tube angle has a minor effect on the flame length and centerline temperature, while increasing the angle enhances air/fuel mixing, as indicated by the decrease in luminosity due to the two elliptical jets' interaction.
Today's gas turbine technology is established in a wide range of applications, including (i) the production of electrical power, (ii) thrust generation in turbojets and (iii) driving large size pumps and compressors. The greatest advantages of gas turbines against other prime mover systems e.g. steam turbine systems and piston engine systems, lie in its higher specific power, compact design and low initial costs based on power output. A major problem in gas turbine combustors is combustion instabilities which may cause many undesirable effects including; (a) increased noise levels, (b) oscillating thrust, (c) mechanical vibration that may lead to serious damage and even total loss of the system. These instabilities are characterized by large oscillations of the flow parameters, which in many circumstances may result in the inability of the combustion process to sustain these large oscillations; leading to partial or total flame blow-off. These combustion oscillations could, however be desirable as in pulsed combustors; as it enhance combustion intensity, increase thermal efficiency and reduce the emission of pollutants like NOx, CO and soot. In light of the above mentioned concepts, the present study is directed towards extending the previous studies on the recently introduced turbojet EV burner having twocircumferential swirling entry air passages by a fourcircumferential swirling air entries configuration. This burner design concept appears to offer many advantages, including: The replacement of the traditional fixed vane swirler by circumferential swirling air passages; and hence not only minimizes blockage and allows prior premixing of fuel and air within the conically shaped entry section to the combustor but also eliminates possible risk in case of swirler blade damage. The study is an experimental investigations of the acoustic signature of a newly designed 4-slot EV burner. All the results are to be compared with those obtained by the previously developed 2-slot configuration. This allows the identification of the merits and/or drawbacks of both designs.
The basic mechanisms leading to combustion oscillations is in the presence of pressure waves, the flow features large scale motions which drive the instability. The dynamics of the flame is then dominated by processes of hydrodynamic instability, vortex roll-up, vortex interactions, front and reacting stream pulsations, periodic extinctions and resignations, self-acceleration. Combustion instabilities are a major problem in the design of high performance propulsion systems (rocket motors, jet engine afterburners, ramjets). Instabilities are also observed in power plants and in various industrial processes. They are characterized by large oscillations of the flow parameters, which have many undesirable effects. Low frequency oscillations induce large mechanical vibrations in the system, including the combustion chamber, the feeding lines and the connected rotating machinery. Unstable operation enhances, the heat transfer rates at the combustor walls and in extreme cases this may lead to serious damage and even a total loss of the system. The present work investigates the changes induced by pilot injections in the acoustic signature of a newly designed 4slot EV burner using pilot injector at reacting and nonreacting conditions. These changes are affecting the flame stabilization especially in the lean premixed combustion due to the large structures resulting from vortex breakdown and the swirling shear-layers. Pilot injector offered good results in flame stability. The injector position influences the flow field and in turns the flame stability. Different pilot injector fuel shift inside the burner are tested. All the results are to be compared with those obtained by the previously developed 2-slot and 4-slot configuration without pilot injector. This allows the identification of the merits and/or drawbacks of both designs.
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