Cross flow fuel injection is a widely used approach for injecting liquid fuel in gas turbine combustors and afterburners due to the higher penetration and rapid mixing of fuel and the cross flowing airstream. Because of the very limited residence time available in these combustors it is essential to ensure that smaller drop sizes are generated within a short axial distance from the injector in order to promote effective mixing. This requirement calls for detailed investigations into spray characteristics of different injector configurations in a cross-flow environment for identifying promising configurations. The drop size characteristics of a liquid jet issuing from a forward angled injector into a cross-flow of air were investigated experimentally at conditions relevant to gas turbine afterburners. A rig was designed and fabricated to investigate the injection of liquid jet in subsonic cross-flow with a rectangular test section of cross section measuring 50 mm by 70 mm. Experiments were done with a 10 degree forward angled 0.8 mm diameter plain orifice nozzle which was flush mounted on the bottom plate of test section. Laser diffraction using Malvern Spraytec particle analyzer was used to measure drops size and distributions in the near field of the spray. Measurements were performed at a distance of 70 mm from the injector at various locations along the height of the spray plume for a reasonable range of liquid flow rates as in practical devices. The sprays were characterized using the non dimensional parameters such as the Weber number and the momentum flux ratio and drop sizes were measured at three locations along the height of the spray from the bottom wall. The momentum flux ratio was varied from 5 to 25. Results indicate that with increase in momentum flux ratio the SMD reduced at the specific locations and an higher overall SMD was observed as one goes from the bottom to the top of the spray plume. This was accompanied by a narrowing of the drop size distribution.
The concept of endothermic fuels is not a strange thing to the aeronautical community. Research is going on, globally, to achieve these kinds of fuels experimentally; but restricted to laboratory scale test setup. This is because of the stringent and controlled method of cracking the fuel thermally as well as catalytically. In this research work we have followed a systematic approach, i.e, developed a laboratory scale reactor for the preliminary feasibility studies and a realistic experimental set up, for the development and analysis of the cracked fuel by simulating the conditions of combustor walls. Developing this technology indigenously involves many steps, namely identification of the suitable catalysts, developing the technology of preparation of catalytically active coatings and then the design and fabrication of the catalytic cracking core. Finally the catalytic cracking core has to be integrated to the test combustor with the experimental setup. To carry out the catalytic cracking reaction, a high pressure and high temperature catalytic reactor was designed and developed. The reactor can heat kerosene up to 725 K and maintain pressures up to 10 bar. The catalytic coatings were prepared with ZSM-5 and molecular sieves (20:80); coated on aluminum cylinders. A temperature drop of 114 K was obtained when kerosene fuel was passed through the catalytic system. This clearly shows the cooling effect by the endothermic fuel. A mixed bed catalytic system (Molecular sieves, Reformax-100 and ZSM-5) was also developed for the in-situ generation of Hydrogen gas along with the catalytic cracking process. The presence of Hydrogen gas in the cracked fuel is confirmed by gas chromatographic (GC) Retention time Vs Voltage investigation. The experimentation in test rig was carried out in two modes, one is for thermal cracking (absence of catalyst) of kerosene fuel and the other one is catalytic cracking. In both the cases, the combustor duct is heated by hot air to 1200 K. Skin temperatures were measured to study the cooling effect of the endothermic fuel and the results are reported in this paper. It is noticed that the chemical composition of the kerosene fuel has been changed and fragmented into lighter chains. It is evident in the Gas Chromatography results that the catalytically cracked kerosene samples (gaseous and liquid samples) are having 30% higher of lighter chains (Ethane, Propane and Butane) of chemical compounds than thermally cracked kerosene samples. As expected, the fuel has got cracked thermally and catalytically while cooling the wall of the duct (simulating the actual flight conditions to realize the practical feasibility of generating endothermic fuels rather than restricting it to laboratory scale experiments).
The flow field associated with a liquid jet injected transversely into a crossflow, also referred as transverse jet has numerous applications in industrial, environmental and natural systems. Examples of these applications include air-breathing engines (gas turbine afterburners, ramjet and scramjet combustors), rocket engines, environmental control systems and natural flows. Earliest research of a jet in a crossflow has been motivated by applications related to environmental problems such as plume dispersal from exhaust or pipe stacks or liquid effluent dispersal in streams. This method of liquid fuel/air mixture preparation enhances flame stabilization, fuel conversion efficiency, and reduction in emissions. In gas turbine applications because of the very limited residence time available for effective fuel air mixing, detailed investigations into spray characteristics of different injector configurations in a crossflow environment is desirable for identifying promising configurations with measurements in the near field to acquire reliable spray data for development of CFD models. The velocity field of a liquid jet in the near field ejecting out from an elliptic injector into a crossflow of air were investigated experimentally at conditions relevant to gas turbine applications. A rig was set up to investigate the injection of liquid jet in subsonic cross flow with a rectangular test section of cross section measuring 100 mm by 140 mm. Experiments were done with a two injector configurations a circular 0.8mm diameter plain orifice injector and a elliptic injector with an equivalent effective area of 0.7 mm (minor axis) by 0.95 mm (major axis) which was flush mounted on the bottom plate of test section. PIV technique was used to measure droplet velocity field and distributions in the near field of the spray. Measurements were performed at a distance of 5 mm from the bottom wall in the span wise plane and the results were compared with a circular injector. It was seen that no significant differences were observed in the u and v velocity components for the elliptic and circular injectors where the geometry changes are small suggesting that parameters like velocity are not significantly affected by small changes in injector exit geometry. Further for elliptic jets it was observed that increasing the crossflow velocity and maintaining the same liquid flow rate lead to an increase in the lateral spread of the spray with no significant change in the mean vorticity values.
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