Zeng-guang Yuan

Detection of Smoke from Microgravity Fires

The history and current status of spacecraft smoke detection is discussed including a review of the state of understanding of the effect of gravity on the resultant smoke particle size. The results from a spacecraft experiment (Comparative Soot Diagnostics (CSD)) which measured microgravity smoke particle sizes are presented. Five different materials were tested producing smokes with different properties including solid aerosol smokes and liquid droplets aerosol smokes. The particulate size distribution for the solid particulate smokes increased substantially in microgravity and the results suggested a corresponding increase for the smokes consisting of a liquid aerosol. A planned follow on experiment that will resolve the issues raised by CSD is presented. Early results from this effort have provided the first measurements of the ambient aerosol environment on the ISS (International Space Station) and suggest that the ISS has very low ambient particle levels.

Measurement of Smoke Particle Size under Low-Gravity Conditions

Smoke detection experiments were conducted in the Microgravity Science Glovebox (MSG) on the International Space Station (ISS) during Expedition 15 in an experiment entitled Smoke Aerosol Measurement Experiment (SAME). The preliminary results from these experiments are presented. In order to simulate detection of a prefire overheated-material event, samples of five different materials were heated to temperatures below the ignition point. The smoke generation conditions were controlled to provide repeatable sample surface temperatures and air flow conditions. The smoke properties were measured using particulate aerosol diagnostics that measure different moments of the size distribution. These statistics were combined to determine the count mean diameter which can be used to describe the overall smoke distribution.

Measurement of gas-phase temperatures in flames with a point-diffraction interferometer

Experiments were performed to evaluate the performance of a point-diffraction interferometry (PDI) system to measure gas-phase temperatures in flames. PDI is an interferometric technique that creates the reference beam after the laser beam passes through the test section and directly provides the index of refraction in two dimensions. PDI-based temperature measurements were compared with thermocouple measurements of two-dimensional and axisymmetric thermal boundary layers, as well as two-dimensional and axisymmetric diffusion flames. The PDI system provided excellent agreement in the measurement of thermal profiles in the boundary layers and was within the uncertainties that are due to the radiation corrections for the thermocouple-based flame temperature measurements.

Smoke Characterization and Feasibility of the Moment Method for Spacecraft Fire Detection

The Smoke Aerosol Measurement Experiment (SAME) has been conducted twice by the National Aeronautics and Space Administration and provided real-time aerosol data in a spacecraft micro-gravity environment. Flight experiment results have been recently analyzed with respect to comparable ground-based experiments. The ground tests included an electrical mobility analyzer as a reference instrument for measuring particle size distributions of the smoke produced from overheating five common spacecraft materials. Repeatable sample surface temperatures were obtained with the SAME ground-based hardware, and measurements were taken with the aerosol instruments returned from the International Space Station comprising two commercial smoke detectors, three aerosol instruments, which measure moments of the particle size distribution, and a thermal precipitator for collecting smoke particles for transmission electron microscopy (TEM). Moment averages from the particle number concentration (zeroth moment), the diameter concentration (first moment), and the mass concentration (third moment) allowed calculation of the count mean diameter and the diameter of average mass of smoke particles. Additional size distribution information, including geometric mean diameter and geometric standard deviations, can be calculated if the particle size distribution is assumed to be lognormal. Both unaged and aged smoke particle size distributions from ground experiments were analyzed to determine the validity of the lognormal assumption. Comparisons are made between flight experiment particle size distribution statistics generated by moment calculations and microscopy particle size distributions (using projected area equivalent diameter) from TEM grids, which have been returned to the Earth. Copyright 2015 American Association for Aerosol Research

Particle Morphology and Size Results from the Smoke Aerosol Measurement Experiment-2

Results are presented from the Reflight of the Smoke Aerosol Measurement Experiment (SAME-2) which was conducted during Expedition 24 (July-September 2010). The reflight experiment built upon the results of the original flight during Expedition 15 by adding diagnostic measurements and expanding the test matrix. Five different materials representative of those found in spacecraft (Teflon, Kapton, cotton, silicone rubber and Pyrell) were heated to temperatures below the ignition point with conditions controlled to provide repeatable sample surface temperatures and air flow. The air flow past the sample during the heating period ranged from quiescent to 8 cm/s. The smoke was initially collected in an aging chamber to simulate the transport time from the smoke source to the detector. This effective transport time was varied by holding the smoke in the aging chamber for times ranging from 11 to 1800 s. Smoke particle samples were collected on Transmission Electron Microscope (TEM) grids for post-flight analysis. The TEM grids were analyzed to observe the particle morphology and size parameters. The diagnostics included a prototype two-moment smoke detector and three different measures of moments of the particle size distribution. These moment diagnostics were used to determine the particle number concentration (zeroth moment), the diameter concentration (first moment), and the mass concentration (third moment). These statistics were combined to determine the diameter of average mass and the count mean diameter and, by assuming a log-normal distribution, the geometric mean diameter and the geometric standard deviations can also be calculated. Overall the majority of the average smoke particle sizes were found to be in the 200 nm to 400 nm range with the quiescent cases producing some cases with substantially larger particles.

Design and Analysis of a Handheld Fire Extinguisher for the Crew Exploration Vehicle

Prior work has revealed the unique aspects of fire suppression in reduced gravity and presented the results of trade studies for both the Crew Exploration Vehicle (CEV) and Lunar landers. The trade studies for both spacecraft showed that water mist systems are the best solution; extremely effective, non-toxic, easy clean-up and minimal interference with spacecraft life support systems. The only downside to water mist is the relatively low Technology Readiness Level (TRL). In the event that the TRL for water mist does not accelerate to a suitable level, the trade analyses showed that water-based foam agents represent an acceptable alternative. There exists no standardized design or testing protocol for spacecraft fire suppression systems (either handheld or total flooding designs). This paper discusses the design of handheld extinguishers, the design of standardized acceptance tests for candidate extinguishers and the results of tests for both water-based foam and water-mist extinguishers.

Spacecraft Fire Detection: Smoke Properties and Transport in Low-Gravity

Results from a recent smoke particle size measurement experiment conducted on the International Space Station (ISS) are presented along with the results from a model of the transport of smoke in the ISS. The experimental results show that, for the materials tested, a substantial portion of the smoke particles are below 500 nm in diameter. The smoke transport model demonstrated that mixing dominates the smoke transport and that consequently detection times are longer than in normal gravity.

Smoke Aerosol Measurement Experiment-2: Comparison of Flight Experiment Results with Ground Test Results

The Re-flight of the Smoke Aerosol Measurement Experiment (SAME-2) was conducted during Expedition 24 (July-September 2010) and flight experiment results have been analyzed with respect to comparable ground-based experiment results. The ground tests included a reference instrument for measuring particle size distributions of the smoke from SAME-2 materials (Teflon, Kapton ® , cotton, silicone rubber and Pyrell ® ). Repeatable sample surface temperatures were obtained with SAME engineering hardware and measurements were taken with returned flight diagnostic equipment consisting of a thermal precipitator for collecting smoke particles for Transmission Electron Microscopy (TEM), several aerosol instruments, and a commercial smoke detector. These flight units measured moments of the particle size distribution: particle number concentration (zeroth moment), the diameter concentration (first moment), and the mass concentration (third moment). The count mean diameter of the smoke particles and the diameter of average mass can be calculated from moment averages. Furthermore, the geometric mean diameter and geometric standard deviations can be calculated if the particle size distribution is assumed to be lognormal. The flight system also included International Space Station and Space Shuttle smoke detectors and the results from these devices are presented. A Scanning Mobility Particle Sizer Spectrometer (SMPS) is too large and complex to include in a flight experiment, but its use in ground-based testing determined whether the lognormal assumptions were valid, and provided high-resolution particle size distributions of the smoke from each material. SMPS particle size distributions from ground experiments were compared to particle statistics generated by moment calculations and particle size

Laminar Smoke Points in Coflow Measured Aboard the International Space Station

Laminar smoke points were measured in nonbuoyant laminar jet diffusion flames in coflowing air aboard the International Space Station as part of the Smoke Point in Coflow Experiment. Smoke points were found for ethylene, propane, propylene, and mixtures of 50% and 75% propylene by volume in nitrogen. Burner diameters were 0.41, 0.76, and 1.6 mm and coflow velocities varied from 5.4 – 65 cm/s. These flames afford unprecedented control over residence time via variations in dilution, burner diameter, and coflow velocity. Increasing coflow velocity decreases luminous flame lengths, but yields longer smoke points. Smaller burners also yield longer smoke points. These trends can be explained qualitatively by considering residence time and radiative loss effects. The luminous flame lengths generally correlate with fuel mass flow rate divided by stoichiometric mixture fraction, although they increase slightly for conditions with high fuel to coflow velocity ratios.

Properties of Smoke from Overheated Materials in Low- Gravity

Smoke particle size measurements were obtained under low-gravity conditions by overheating several materials typical of those found in spacecraft. The measurements included integral measurements of the smoke particles and physical sample of the particles for Transmission Electron Microscope analysis. The integral moments were combined to obtain geometric mean particle sizes and geometric standard deviations. These results are presented with the details of the instrument calibrations. The experimental results show that, for the materials tested, a substantial portion of the smoke particles are below 500 nm in diameter.