Microgravity Combustion Diagnostics Workshop

Through the Microgravity Science and Applications Division (MSAD) of the Office of Space Science and Applications (OSSA) at NASA Headquarters, a program entitled, Advanced Technology Development (ATD) was promulgated with the objective of providing advanced technologies that will enable the development of future microgravity science and applications experimental flight hardware. Among the ATD projects one, Microgravity Combustion Diagnostics (MCD), has the objective of developing advanced diagnostic techniques and technologies to provide nonperturbing measurements of combustion characteristics and parameters that will enhance the scientific integrity and quality of microgravity combustion experiments. As part of the approach to this project, a workshop was held on July 28 and 29, 1987, at the NASA Lewis Research Center. A small group of laser combustion diagnosticians met with a group of microgravity combustion experimenters to discuss the science requirements, the state-of-the-art of laser diagnostic technology, and plan the direction for near-, intermediate-, and long-term programs. This publication describes the proceedings of that workshop

Visualization and imaging methods for flames in microgravity

The visualization and imaging of flames has long been acknowledged as the starting point for learning about and understanding combustion phenomena. It provides an essential overall picture of the time and length scales of processes and guides the application of other diagnostics. It is perhaps even more important in microgravity combustion studies, where it is often the only non-intrusive diagnostic measurement easily implemented. Imaging also aids in the interpretation of single-point measurements, such as temperature, provided by thermocouples, and velocity, by hot-wire anemometers. This paper outlines the efforts of the Microgravity Combustion Diagnostics staff at NASA Lewis Research Center in the area of visualization and imaging of flames, concentrating on methods applicable for reduced-gravity experimentation. Several techniques are under development: intensified array camera imaging, and two-dimensional temperature and species concentrations measurements. A brief summary of results in these areas is presented and future plans mentioned

New findings and instrumentation from the NASA Lewis microgravity facilities

The study of fundamental combustion and fluid physics in a microgravity environment is a relatively new scientific endeavor. The microgravity environment enables a new range of experiments to be performed since: buoyancy-induced flows are nearly eliminated; normally obscured forces and flows may be isolated; gravitational settling or sedimentation is nearly eliminated; and larger time or length scales in experiments become permissible. Unexpected phenomena have been observed, with surprising frequency, in microgravity experiments, raising questions about the degree of accuracy and completeness of the classical understanding. An overview is provided of some new phenomena found through ground-based, microgravity research, the instrumentation used in this research, and plans for new instrumentation

Low thrust chemical rocket technology

An on-going technology program to improve the performance of low thrust chemical rockets for spacecraft on-board propulsion applications is reviewed. Improved performance and lifetime is sought by the development of new predictive tools to understand the combustion and flow physics, introduction of high temperature materials and improved component designs to optimize performance, and use of higher performance propellants. Improved predictive technology is sought through the comparison of both local and global predictions with experimental data. Predictions are based on both the RPLUS Navier-Stokes code with finite rate kinetics and the JANNAF methodology. Data were obtained with laser-based diagnostics along with global performance measurements. Results indicate that the modeling of the injector and the combustion process needs improvement in these codes and flow visualization with a technique such as 2-D laser induced fluorescence (LIF) would aid in resolving issues of flow symmetry and shear layer combustion processes. High temperature material fabrication processes are under development and small rockets are being designed, fabricated, and tested using these new materials. Rhenium coated with iridium for oxidation protection was produced by the Chemical Vapor Deposition (CVD) process and enabled an 800 K increase in rocket operating temperature. Performance gains with this material in rockets using Earth storable propellants (nitrogen tetroxide and monomethylhydrazine or hydrazine) were obtained through component redesign to eliminate fuel film cooling and its associated combustion inefficiency while managing head end thermal soakback. Material interdiffusion and oxidation characteristics indicated that the requisite lifetimes of tens of hours were available for thruster applications. Rockets were designed, fabricated, and tested with thrusts of 22, 62, 440 and 550 N. Performance improvements of 10 to 20 seconds specific impulse were demonstrated. Higher performance propellants were evaluated: Space storable propellants, including liquid oxygen (LOX) as the oxidizer with nitrogen hydrides or hydrocarbon as fuels. Specifically, a LOX/hydrazine engine was designed, fabricated, and shown to have a 95 pct theoretical c-star which translates into a projected vacuum specific impulse of 345 seconds at an area ratio of 204:1. Further performance improvment can be obtained by the use of LOX/hydrogen propellants, especially for manned spacecraft applications, and specific designs must be developed and advanced through flight qualification

Equipment concept design and development plans for microgravity science and applications research on space station: Combustion tunnel, laser diagnostic system, advanced modular furnace, integrated electronics laboratory

Taking advantage of the microgravity environment of space NASA has initiated the preliminary design of a permanently manned space station that will support technological advances in process science and stimulate the development of new and improved materials having applications across the commercial spectrum. Previous studies have been performed to define from the researcher's perspective, the requirements for laboratory equipment to accommodate microgravity experiments on the space station. Functional requirements for the identified experimental apparatus and support equipment were determined. From these hardware requirements, several items were selected for concept designs and subsequent formulation of development plans. This report documents the concept designs and development plans for two items of experiment apparatus - the Combustion Tunnel and the Advanced Modular Furnace, and two items of support equipment the Laser Diagnostic System and the Integrated Electronics Laboratory. For each concept design, key technology developments were identified that are required to enable or enhance the development of the respective hardware

Optical measurement methods in thermogasdynamics

A review is presented of a number of optical methods of flow measurements. Consideration is given to such spectroscopic methods as emission and absorption techniques, electron beam-stimulated fluorescence, and light scattering - Rayleigh, Raman and Mie - methods. The following visualization methods are also discussed: shadow photography, schlieren photography, interferometry, holographic interferometry, laser anemometry, particle holography, and electron-excitation imaging. A large bibliography is presented and the work is copiously illustrated with figures and photographs

Laser Diagnostic Techniques with Ultra-High Repetition Rate for Studies in Combustion Environments

When conducting laser based diagnostics in combustion environments it is often desirable to obtain temporally resolved information. This can be due to several factors such as combustion taking place in a turbulent flow field, flame propagation from a spark plug in an initially quiescent combustible mixture, or rapid, multi-point fuel consumption in a homogeneous charge as a result of compression ignition in an engine cycle. A multi-YAG laser cluster and a high-speed framing camera capable of recording sequences of up to eight image frames, and having a framing rate up to the megahertz range were originally set up for these types of studies. Within the framework of this thesis, further developments of this high-speed diagnostic system aiming at extending the wavelength palette and thus the range of detectable species, was carried out. In addition, the system was used for measurements with ultra-high repetition rates for the detection of different flame species in a variety of combustion devices. The high-speed laser system was redesigned for the generation of laser radiation at 355 nm, in addition to the original 532 nm and 266 nm, and a successful feasibility test for high-speed formaldehyde planar laser-induced fluorescence (PLIF) was carried out for the new design. Moreover, a novel multi-dye laser cluster has been set up. By pumping each of the four dye lasers individually using the Nd:YAG lasers in the multi-YAG cluster, tunable laser radiation with an ultra-high repetition rate can be produced, without the drawback of either losses in laser pulse energy or significant deterioration of the beam intensity profile often occurring when a single dye laser is pumped at ultra-high repetition rates. The multi-YAG and multi-dye laser clusters were used for high-speed visualization of the OH radical by means of planar laser-induced fluorescence in a low-swirl methane/air flame for tracking flame front movements over time while simultaneously measuring the flow-velocity field. Simultaneous high-speed OH visualization and imaging of the temperature field was also performed. The work carried out was a first step in the development of a detailed Large Eddy Simulation validation database for turbulent, premixed methane/air flames. High-speed OH PLIF using a single dye laser was employed in several other studies of the reaction zone, including an investigation of the ignition properties of hot jets in explosive environments, a study of combustion processes in a pulse combustor, and an investigation of the governing processes leading to electrical signals in an ion-current sensor. The last of these also included high-speed fuel tracer LIF. An alternative technique for flame studies involving measurement of the chemiluminescence from OH and CH in order to determine the equivalence ratio was investigated in terms of spatial and temporal resolution. The capability of the technique for resolving flame fronts was compared to reference measurements of OH PLIF. The tests showed that the spatial resolution in the depth direction suffered from line-of-sight detection, which significantly reduced the resolution. As the sensor was designed for monitoring spatial and temporal inhomogenities in mixtures within industrial gas turbine combustors, the temporal and spatial scales in such a combustor were evaluated using the high-speed laser diagnostic system for time-resolved visualization of OH. Also, fuel tracer PLIF was performed in order to visualize the fuel distribution in the combustor. The multi-YAG laser cluster was used in several studies of combustion processes in a homogeneous charge compression ignition (HCCI) engine, involving both high-speed fuel tracer PLIF and formaldehyde PLIF, with the aim of studying different types of ignition control. Acetone was used as a fuel tracer in investigating the effects of combustion chamber geometry on combustion. In studies of spark-assisted HCCI operation, the engine was run on a fuel mixture containing n-heptane, which produces formaldehyde early in the cool-flame region. Formaldehyde can thus be used as a fuel marker, eliminating the need of an added fuel tracer in this situation. Furthermore, three-dimensional imaging of formaldehyde in a laboratory flame as well as of Jet-A vapour in a slow non-reacting flow was demonstrated. This was achieved by rapidly scanning the laser sheet across a measurement volume spatially separating the eight laser pulses. A stack of closely spaced PLIF images was acquired by the framing camera, which could be used to re-create the three-dimensional shape of the investigated species by means of interpolation between the sheets

JANNAF Liquid Rocket Combustion Instability Panel Research Recommendations

The Joint Army, Navy, NASA, Air Force (JANNAF) Liquid Rocket Combustion Instability Panel was formed in 1988, drawing its members from industry, academia, and government experts. The panel was chartered to address the needs of near-term engine development programs and to make recommendations whose implementation would provide not only sufficient data but also the analysis capabilities to design stable and efficient engines. The panel was also chartered to make long-term recommendations toward developing mechanistic analysis models that would not be limited by design geometry or operating regime. These models would accurately predict stability and thereby minimize the amount of subscale testing for anchoring. The panel has held workshops on acoustic absorbing devices and combustion instability computational methods. At these workshops, research projects that would meet the panel's charter were suggested. The panel's conclusions about the work that needs to be done and recommendations on how to approach it, based on evaluation of the suggested research projects, are presented