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Fuel sprays for aerospace propulsion systems tend to have high optical densities which causes difficulties in making quantitative measurements using conventional diagnostics. Using advance photon tools such as X-ray radiography can overcome some of these issues. These slides summarize some of the issuers related to rocket sprays and provides an overview of the X-ray methods that have been applied to date., The original document contains color images.

Shear coaxial injectors are a common injector type for liquid-rocket-propulsion applications and can be found in many oxygen/hydrogen engines. These injectors rely on the shear between an outer lower-density, high-velocity annulus and a higher-density, low-velocity inner jet to atomize and mix the propellants. Because of the dense-jet core, the optical densities of these sprays are high, particularly near the injector where primary atomization and flame holding take place. The large optical density has prevented interrogation, detailed study, and understanding of this important region. The evolution of x-ray radiography techniques using intense x-ray sources (such as Argonne National Laboratory's Advanced Photon Source) has allowed the measurement of quantitative equivalent path lengths and projected densities in the near-injector regions of shear coaxial injectors. Using water and gaseous nitro-gen as propellant simulants at atmospheric backpressure, the effect of momentum flux ratio and mass flux ratio, are investigated for three injector geometries operating at momentum flux ratios spanning the range from 0.5 to 15., The original document contains color images. Presented at the Annual ILASS-Americas Conference (25th) held in Pittsburgh, PA on 5-8 May 2013.

Current limitations in available data and computational tools have led to an on-going reliance on experimental measurements for injector design. Unfortunately, the mass flow rates typically encountered in rocket engines create sprays with high optical densities and render the vast majority of optical and laser techniques ineffective. Data has been obtainable through mechanical patternation, but the technique has limitations especially near the injector. Time-gated ballistic imaging has also shown promise in rocket injectors but produces only qualitative information about the mass flux. An x-ray radiographic technique with a high-power x-ray source (the Advanced Photon Source at Argonne National Laboratory) has been applied to these high optical- density sprays. To achieve this testing a mobile flow facility was constructed; this facility simulates the rocket flows using water and nitrogen instead of fuel and oxidizer. The x-ray radiography technique can be applied in two ways. Time-averaged measurements provide information related to the mass flux and droplet velocity while time-resolved measurements have the ability to provide droplet size and velocity distributions. Both techniques have been applied toa specific injector type of interest in rocket propulsion, a gas-centered swirl-coaxial injector, and the results are used to show the complexities and strengths of x-ray radiography and illustrate the types of useful information that can be extracted, information that will aid in the development and improvement of rocket injectors., The original document contains color images. Presented at the JANNAF (7th LPS section) held in Colorado Springs, CO in June 2013. Prepared in cooperation with Argonne National Laboratory, Argonne, IL.

Gas-centered swirl coaxial injectors, a specific type of airblast atomizer, are of interest in rocket propulsion applications. These applications require good mixing of the liquid and gas to ensure complete combustion within the engine. While strides are being made on the computational front, predictions of the mass distributions achieved with this type of injector remain too costly or too inaccurate for engineering design. There has been, therefore, a reliance on experimental results. Unfortunately, the mass flow rates and the strong gas phase typically encountered in rocket engines create sprays with high optical densities and render the vast majority of optical and laser techniques ineffective. Data has been obtainable through mechanical patternation, but the technique has limitations. Time-gated ballistic imaging has also shown promise in rocket injectors but produces only qualitative information. An x-ray radiographic technique with a high-brilliance x-ray source (Advanced Photon Source) has been applied to these high-optical-density sprays. To achieve this testing a new, mobile flow facility was constructed; this facility simulates the rocket flows using water and nitrogen instead of fuel and oxidizer. The x-ray radiography technique has been able to measure equilvent path length in gas-centered swirl coaxial injectors at a range of typical operating conditions. These results and their implications for gas-centered swirl coaxial injector performance in liquid rocket engines are discussed., For presentation at the 12th International Conference on Liquid Atomization and Spray Systems (ICLASS), Heidelberg, Germany, 2-6 Sep 2012. The original document contains color images.

Tailored injectors near the wall of a combustion chamber are often an integral part of a rocket engine's thermal management. However, most studies of injectors utilize single, isolated elements. The ability of walls to affect the expansion and stability of single-phase jets has already been well established. The effect of a wall on a multiphase flow, a spray, has not been established. Reported here is the impact a single wall has on the behavior of a spray from a single injector. Of specific interest are parameters which may impact engine performance, specifically attachment length, spray growth and stability. The atomizer being studied is a gas-centered swirl coaxial injector which relies on a dominant gas flow to drive the atomization. High-speed images are analyzed to assess the spray's behavior both qualitatively and quantitatively. Three wall offset ratios, 0.57, 0.83 and 1.16, are compared to the free spray. Sprays are qualitatively similar, but the wall has a quantitative effect on spreading rate. The wall is able to decrease the variability in the spray, but not globally-only very near the wall., For presentation at the JANNAF 2011 Joint Subcommittee Meeting, Huntsville, AL, 5-9 Dec 2011.

High-speed movies of optically dense sprays exiting a Gas-Centered Swirl Coaxial (GCSC) injector are subjected to image analysis to determine spray characteristics. As a test for its efficacy in analysis of high-optical-density sprays, Proper Orthogonal Decomposition (POD) was applied to the image sequence prior to image analysis. Results of spray morphology including spray boundary, widths, angles and boundary oscillation frequencies, are compared with and without the application of POD. The most dominant modal reconstructions (between 2 and 5) of the spray are found to be sufficient to quantitatively describe the spray parameters, while the frequency of movement of the spray boundary is well predicted by the first two modes alone. Despite being computationally intensive, preprocessing of spray images using POD has advantages in - a) reduction of droplet noise in the spray boundaries thereby resulting in a smoother boundary for edge detection, and b) ability to process morphological parameters of ill-behaved sprays., To be presented the Annual Conference on Liquid Atomization and Spray Systems (23rd), ILASS Americas, in Ventura, CA, in May 2011.

An in-depth analysis of the uncertainties associated with small-scale rocket engine testing has been conducted. The analysis uses terminology and approaches detailed in the ISO ?Guide to the Expression of Uncertainty in Measurement? (GUM) and a recent NASA handbook on the subject (NASA HBK-8739.19-3). Along with this analysis, best practices for minimizing uncertainties are provided. AFRL?s Experimental Cell-1 facility is used as the example engine, and the data values provided come from this system. The facility is sized to test a single, full-scale element or an array of scaled-down elements producing thrust in the range of 100-500 pounds. The facility has recently completed an overhaul to increase the number of data channels available and to improve accuracy. The measurand being specifically evaluated is c*-efficiency (ηc*). However, details are given on all of the parameters which contribute to the measurement and calculation of this value. This analysis should aid in the design, upgrade, operation and data assessment of EC-1 and other small-scale facilities., Presented at the JANNAF 2011 Joint Subcommittee Meeting Conference held in Huntsville, AL on 5-9 December 2011.

Studies of injectors often utilize a single, isolated atomizer. In most applications, however, the atomizer is not isolated but is near one or more walls. It has been established that walls affect the expansion and stability of single-phase jets. Under study here is the effect of a single wall on spray behavior, specifically attachment length, spreading and stability. The atomizer being studied is a gas-centered swirl coaxial injector which relies on a dominant gas flow to drive the atomization. High-speed images are analyzed to assess the spray's behavior both qualitatively and quantitatively. Two different wall offset ratios, 0.83 and 1.16, are compared to the free spray. While both walls spacings affect the spray by reducing the spreading, only the 0.83 spacing shows an ability to stabilize the spray., For presentation at The Institute for Liquid Atomization and Spray Systems (ILASS)-Americas, Ventura, CA, 16-18 May 2011.

This paper describes subscale, risk-reduction tests of an efficient method for applying a fuel film cooling (FFC) layer to the chamber wall of a liquid-hydrocarbon/gaseous-oxygen boost engine. The method reduces the amount of fuel required to meet wall temperature requirements relative to barrier film cooling approaches, thereby reducing the impact of FFC on specific impulse and contributing to a major AFRL IHPRPT goal for this propulsion category. The test specimens were designed and fabricated by Aerojet Corporation and make use of platelet technology to achieve a precise application of the film cooled layer. The test articles consist of two FFC panels, a calorimeter panel to establish baseline heat flux levels, and two injectors with differing levels of barrier film cooling. The principal measurement for characterizing the effectiveness of the panel designs will be the intact length of the FFC layer which will be measured using a combination of axially resolved heat flux measurements and post-test soot markings. Intact lengths will be measured for a range of fuel film injection flow rates and gas stream conditions. In this paper we report on a series of cold flow visualization tests utilizing stimulant fluids which were performed to provide additional insight into the behavior of the designs with respect to the levels of liquid stripping, entrainment and uniformity of the FFC layers., To be presented at the JANNAF 57th Joint Subcommittee Meeting, held in Colorado Springs, CO, on 3-7 May 2010.

The ability to predict atomizer performance can reduce the cost of system development in many areas. This paper investigates the atomization efficiency and droplet distribution from films with strong gas-phase influences. A prediction of atomization efficiency based on a general theory of the droplet creation process is given. In this process a disturbance is created on the film surface then broken down into droplets via stripping. The theory relates the mass of film lost via atomization to the mass of liquid introduced into the atomizer to predict atomization efficiency and offers some estimations of primary droplet diameter. A specific example involving a gas-centered swirl coaxial injector is given to illustrate how the theory would be applied; however, efforts are made to keep the model as general as possible so that it applies to many types of atomizers and a wide range of operating conditions., Presented at The Institute for Liquid Atomization and Spray Systems Conference (ILASS 2007) in Chicago, IL on 15-18 May 2007.