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Diesel sprays present a challenging environment for detailed quantitative measurement of the liquid field, and to date, there have been only a few efforts to characterize drop sizes within the family of Engine Combustion Network (ECN) diesel sprays. Drop sizing diagnostics, including optical microscopy and Ultra-Small Angle X-ray Scattering (USAXS), have been recently demonstrated in Spray A/D ECN activities, but little data exist to validate these results. This work therefore seeks to extend the available ECN data on the liquid phase field and provide a new comparative data set for assessment of previous ECN drop sizing measurements. In particular, this work presents the development of a two-wavelength, line-of-sight extinction measurement to examine liquid volume fraction and the corresponding droplet field in high-pressure fuel sprays. Here, extinction of lasers emitting at 10.6 μm and 0.633 μm are used for the measurement. To enable quantification of the liquid field in optically dense regions of the spray, a transfer function is developed to account for the influence of multiple scattering. The developed diagnostic is then applied to n-dodecane sprays from the ECN Spray A and Spray D injectors at varying fuel rail pressures and atmospheric chamber condition. Overall, the results show a reasonable agreement with droplet sizes measured using USAXS, as well as from more recent measurements using a Scattering-Absorption Measurement Ratio (SAMR) technique also developed in our group. This is particularly the case near the spray periphery, where on average, less than 40% difference in the measured Sauter mean diameter is observed. Nonetheless, an apparent discrepancy is observed between drop sizes from different diagnostics close to the jet centerline (i.e. nearly 100% difference between available data for Spray D injector). Moreover, the presented diagnostic shows an improved capability in the dilute regions of the spray, where x-ray-based diagnostics are generally subject to high noise and low signal sensitivity.

This paper presents analysis of results from optical diagnostics in a high-pressure combustor burning gaseous oxygen (GOX) and liquid kerosene RP-2 fuel through a jet-swirl coflow injector. The obj...

The “Twin-Fluid Jet-in-Crossflow (TF-JICF)” is a nascent variation of the classical JICF, in which a liquid jet is co-injected with an annular sleeve of gas into a gaseous crossflow. Jet-engine designers are interested in using TF-JICF for liquid-fuel injection and atomization in the next-generation combustors because it is expected to minimize combustor-damaging auto-ignition and fuel-coking tendencies. However, experimental data of TF-JICF are sparse. Furthermore, a widely accepted TF-JICF model that correlates the spray’s penetration to the combined liquid-gas momentum-flux ratio (Jeff) is increasingly showing discrepancy with emerging results, suggesting a gap in the current understanding of TF-JICF. This paper describes an investigation that addressed the gap by experimentally characterizing the TF-JICF produced by a single injector across wide ranges of operating conditions (i.e., jet-A injectant, crossflow of air, crossflow Weber number = 175-1050, crossflow pressure Pcf = 1.8-9.5 atm, momentum-flu...

This paper describes an experimental investigation of the effects of air-assist upon the penetration and dispersion of a liquid fuel jet that is injected into cross-flowing air. The spray patterns across the central longitudinal plane were investigated at flow conditions similar to those encountered at the combustor inlet of a modern gas turbine engine. Temperatures of the cross-flow and assist air were at 316 and 427°C, while test-channel pressures were set at 2.02 and 2.53MPa. Jet-A fuel was injected through a wall-recessed plain orifice into a rectangular test-channel where the cross-flow air velocity was Ucross-flow=75m/s. Assist air was injected from four slots surrounding the fuel orifice within the wall-recessed well. The air-assist jets impinged upon the fuel jet at a 45° angle. Pressure drops across the air-slots were limited to ≤4% of test-channel pressure to simulate the difference between stagnation and static pressures on a typical fuel-air mixer/injector. Thus, the assist-air-to-liquid fuel mass-flow ratios (ALR) were limited to 0.41, which was much lower than those used in traditional airblast atomizers with ALR in the range of 1 to 10. Momentum-flux ratios (J) of the fuel jet to cross-flow were varied between J=5 to 40. A 355nm planar laser was used to illuminate the spray’s central plane to capture images of liquid droplets Mie-scattering. An attempt was made at correlating the trajectories of the jet using an effective momentum-flux ratio Jeff that accounts for air-assist jets’ momentum. It was discovered that air-assist had limited influence on the spray’s outer-edge penetration, while it strongly enhances the penetration of the inner-edge and spray centerline. Air-assist’s effects were also found to be proportional to ALR. Contrary to the results of airblast jet-in-cross-flow researches, it was found that at J∼5, when the sprays’ inner-edges were close to the wall, air-assist enhanced the inner-edge penetration in a manner that was not well-captured by Jeff. Finally, it was also observed that sprays at 2.53MPa were more sensitive to J and air-assist variations than sprays at 2.02MPa.Copyright © 2015 by ASME

This study investigates the autoignition of a Jet-A fuel spray in a preheated air flow in a 75mm inner diameter quartz tube at atmospheric pressure. Fuel was injected via a pressure-swirl atomizing injector enclosed in an aerodynamically-shaped outer body (7mm diameter) that is installed coaxially with the flow using 3 water-cooled pylons. The air temperature and oxygen content were in the range of 1000–1400 K and 9–12%, respectively by controlling the equivalence ratio in the primary zone of the pre-burner/vitiator and by adding dilution air downstream. The co-flow air velocity ranged from 25–30 m/s for this study (Re = 10,000–12,000), with a trapezoidal profile. Fuel spray was characterized using PDPA. Shape of the spray was transitional between hollow and solid cone with the corner angle of 35° to the axis near injector which reduced to 22° downstream. Spray density varied significantly over cross-section of the tube with the minimum on the axes. Droplets produced have average diameters (D10) of 15–70μm on the axes and periphery, respectively, at 6 cm downstream from the injector. Character of the droplet size distribution was polydisperse. Auto-ignition time delays were captured using a time-averaged camera with CH* (432nm) filter. The measured values agree with delay times previously reported in literature. Two synchronized high-speed cameras with 432nm and 307nm filters were used to investigate dynamics of auto-ignition kernel initiation and convection by capturing of CH* and OH* chemiluminescence at 5000 f ps. This methodology allowed qualitative characterization of the equivalence ratio of kernels in process of their convection and growth. It was shown that kernels are always initiated on the axes of the spray where the average droplet size is minimum. Kernels were formed leaner and become richer as they grow down-stream as indicated by the increase of CH*/OH*intensity ratio. Additionally, kernel behavior depends greatly on air temperature with kernels transitioning from randomly appearing (i.e. single kernel), to periodic, to a constantly auto-igniting flame with the spatial scatter of ignition kernels decreasing with temperature.Copyright © 2015 by ASME

This paper describes the development of an empirical approach that attempts to predict blow-out of bluff body stabilized flames using global flow parameters in systems where liquid fuel injectors are located a short distance upstream of the wake. This approach was created on the hypothesis that flame stability in such a combustion system (referred to as a close-coupled injection) is determined by the strength of the heat source developed in the bluff body recirculation zone and by the availability of sufficient contact time with fresh mixture for its ignition, similar in nature to premixed combustion systems. Based on this concept, global equivalence ratio on the classical DeZubay stability map was replaced by local equivalence ratio in the recirculation zone of the bluff body. This local equivalence ratio was determined experimentally using a chemiluminescence measurement system. Tests were conducted using a single bluff body with a close-coupled injection system in a 76 × 152 mm (3 × 6 in.) combustion tunnel. A wide range of fuel–air ratios and velocities were achieved by variation of the global equivalence ratio, incoming flow velocity, and injector size. The obtained experimental dataset was used to develop a transfer function that allowed calculation of the local equivalence ratio in the recirculation zone based on the global flow parameters. Equivalence ratio in the recirculation zone was found to be exponentially dependent upon the square root of the fuel to air momentum flux ratio such that increasing the momentum flux ratio led to a reduction in the recirculation zone equivalence ratio. Additional adjustment of this general trend by the diameter of injector and air flow velocity was necessary to improve the quality of the prediction. The developed approach demonstrated a good prediction of the globally rich blow-out of the flame. In fact, the recirculation zone lean blow-out limit (corresponding with globally rich blow-out) predicted for close coupled injection using the developed transfer function closely coincided with the lean blow-out line of the classical DeZubay envelope and with results obtained with premixed injection using the same bluff body. On the contrary, globally lean (locally rich) blow-out was predicted ∼20% below the DeZubay rich blow-out line, possibly because of the limited range of the fuel flow rates on the experimental rig used.

This study demonstrates a new approach to liquid rocket engine (LRE) design, which permits the suppression of the severe 1-T spinning tangential combustion instability. Presently, control of the spinning tangential wave with a frequency of f ≈ 5000 Hz has been demonstrated in this laboratory reproduced liquid rocket engine combustor using an asymmetric fuel injector distribution. This combustor burns liquid fuel (Jet-A) with preheated air, and is equipped with six “smart” injectors, which have the ability to modify characteristics of their sprays without changing the fuel and oxidizer flow rates. To control the symmetry of the reaction zone, the combustor is equipped with capabilities to operate the spray characteristics of five of the injectors simultaneously, while varying the spray of the sixth injector separately. A high speed camera operating at 30,000 fps was used to take images of the tangential wave, while focusing on the reaction zone from the exhaust. Aside from the high speed camera, three pressure sensors (P’1, P’2 & P’3) and three fiber optic probes (FOP1,2,3) were strategically placed around the combustor. These diagnostic tools provided insight into the characterization associated with controlling the tangential mode instability. During testing, it was found that the high amplitude spinning tangential wave was able to be transformed into a low amplitude standing wave by altering the spray characteristics of the single injector. Across the tests, it was found that this transition in mode was characterized by an approximate 6X decrease in oscillatory pressure amplitude, while remaining at a constant frequency of f ≈ 5000 Hz. From this investigation, it has been suggested that breaking the symmetry of the reaction zone by controlling the spray pattern of a single injector in the group represents a viable LRE design approach to control the detrimental 1-T spinning tangential instability.

The placement of the fuel in combustors is significant for combustor design. Hence the study of the liquid penetration into a crossflow has received attention from various researchers. There have been various correlations suggested for the upper surface of the liquid jet trajectories suggested by several researchers. However, many of these correlations are applicable to specific operating conditions, injector geometries and measurement techniques. This study is an attempt to develop spray trajectory correlations that is applicable to a wide range of operating conditions and injector geometries. Previous studies have shown that the penetration of a spray created by round edged orifice is higher than that created by a sharp edged orifice. The approach is to develop trajectory correlations to the spray created by a round edged orifice that is expected to give the highest penetration. For the injectors of various other geometries, a correction factor is used to obtain the spray trajectories. Preliminary study has shown that the location of the column breakup point obtained by using the liquid jet light guiding technique could possibly be a part of the correction factor to the penetration of the spray. The trajectories of the jet and the location of the column breakup points are obtained for four different injectors at several operating conditions. These results are used for obtaining the correlation for the spray trajectory and the correction factor for the various injectors.

Spray created by Jet A fuel injection from a plate containing sharp edged orifice 0.018 inches (457 µm) in diameter and L/D ratio of 10 into the crossflow of preheated air (555 K) at elevated pressure in the test section (5 atm) was compared to that created by a smooth countersunk injector with a L/D ratio of approximately unity under the same flow conditions. The Weber number (We) of the spray and momentum flux ratio (q) of the spray were also investigated with measurements taken at We=500, 1000, and 1500 and q=10, 20, and 40. The smooth countersink design in the second injector is meant to decrease the turbulence within the fuel injection column. A two component Phase Doppler Particle Analyzer was used for measuring the characteristics of the spray along its centerline. Macro images of the spray were also taken for spray trajectory (outer-edge) measurements. It was found that the core of the spray produced by the smooth countersunk injector penetrates further into the test section away from the injector orifice by approximately 2mm. It was seen that large scale turbulent structures on the order of 0.5-1.0 diameters form on the surface of the liquid column using the sharp edged injector while the liquid jet column produced by the smooth injector has smaller surface wave structures that were of the order of 0.2d. The smooth injector also produces droplets with a smaller mean diameter (D10), especially close to the orifice. Meanwhile, droplets from this injector that are close to the wall have a higher average velocity in the direction of fuel injection.