The FLEX experiment was designed to assess and quantify the effectiveness
of inert-gas suppressants in microgravity and obtain the most conservative
estimate of the limiting oxygen index for steady combustion. FLEX
is studying the behavior of near-limit diffusion flames examining
in detail liquid- and gas-phase transport and chemical kinetics, and
developed and is validating detailed and reduced-order transport and
chemistry models that are the foundation for real engine simulations.
8th US National Combustion Meeting, May 19-22, 2013, Salt Lake City, Utah, USA
• “Isolated alkane droplet combustion in microgravity: ”Cool Flames” T. Farouk and F.L. Dryer (Paper#1H17)
• Effect of varying the initial diameter of n-octane and n-decane droplets over a wide range on the spherically symmetric combustion process: International Space Station Experiments,” Y.C. Liu, K.N. Trenou, J. Rah, M.C. Hicks, C.T. Avedisian (paper# 2G11)
• “Methanol droplet combustion in oxygen-inert environments in microgravity,” V. Nayagam, D.L. Dietrich, M.C. Hicks, F.A. Williams (paper#2G10)
• “Computational modeling of the effects of support fibers on evaporation of fiber-supported droplets in reduced gravity,” N. Ghatta and B.D. Shaw (Paper#070HE-0020).
• The FLEX testing that occurred on Feb 21, 2013, completes the FLEX science matrix dedicated to the CO2 Diluent Exchange Series of tests.
• Testing was performed with MeOH droplets in a chamber at 3 atm pressure in two different chamber compositions; the first was 21% O2 / 75% CO2 / balance N2 and the second test atmosphere, representing a return to a previous atmosphere that was unsuccessful, was a composition of 21% O2 / 50% CO2 / balance N2.
• In both atmospheres, with the larger droplet diameters (i.e., Do = 6 mm), some peculiar flame asymmetries were observed that are difficult to explain without further analysis of the recorded data. It is not clear if these flame asymmetries are due to fiber effects, that may be pronounced because of the elevated pressures and high diluent concentrations, or are artifacts of fuel quality. These tests have to be carefully analyzed and compared with earlier MeOH tests.
• At a later date, additional Diluent Exchange Tests will be performed using Helium and Xenon as the diluents. These complementary tests will provide an excellent basis for comparing the effects of gas radiation (CO2) and thermal and mass diffusion rates; He (high) and Xenon (low). Testing with these gases will also help shed light on the mechanisms driving the phenomena of spontaneous auto-ignition recently observed with n-heptane in elevated atmospheres.
December 2011: The FLEX Science and Engineering
teams have accomplished the majority of the FLEX science
operations. As of December 13, 2011, FLEX has accomplished
225 unique test points; 82 of which have been taken since
August 8, 2011. All FLEX fuel reservoirs on ISS have
been depleted. Two additional fuel reservoirs (one
heptane and one methanol) are planned to be launched on the
HTV-3 flight, currently scheduled for July 31, 2012. These
fuels will allow for the completion of the Helium test point
section of the FLEX science matrix and for the inclusion
of droplet burns using Xenon diluent gas mixes. Once
these final two fuel reservoirs are depleted the FLEX investigation
will come to an official end. In the meantime, the
CIR has been reconfigured to run the FLEX-2 investigation,
which will start in January 2012. A new radiometer
package and FLEX-2 fuels were installed into the CIR on December
20, 2011. (See FLEX-2 for additional information.)
Scott: Thank you for your hard work replacing
a CIR manifold bottle and closing and opening bottle valves
to support the calibration of CIR's FOMA (Fuel/Oxidizer Management
Assembly) on GMT 039. This calibration needs to be completed
yearly to ensure that all the pressure transducers in the
CIR are accurate. Also, we appreciate your efforts to replace
the MDCA needles and fiber arm on GMT 040. Great job making
up time in the schedule! We are going to re-evaluate the
duration of these activities based on your suggestion.
January 2011 - Two Flame Extinguishment
Experiment (FLEX) test points to determine diffusion extinction
limits in very low oxygen concentrations were completed on
January 12, 2010. The total number of test points achieved
to date is 128 of 258 planned. Newly designed, electrically
conductive fuel deployment needle assemblies are still on
track for launch on HTV-2.
December 2010 -Four Flame Extinguishment Experiment
(FLEX) test points were taken on December 28, 2010. The
total number of tests achieved to date is 126 of 258 planned.
• Multiple test points for the Multi-use Droplet Combustion Apparatus’ Flame Extinguishment Experiment (MDCA/FLEX) were run on April 19, 2010. All were successful to at least some degree and good science data was collected. This data will be transferred and downlinked to ground next week. Three test points from the science matrix were accomplished.
• Test #1 - Droplet diameter of 4 mm, with no support fiber. Droplet deployment was successful with a brief burn before radiative extinction. An afterglow from condensing vapor cloud and scattered backlight occurred approximately 30 sec after extinction. This afterglow phenomena typically occurs following radiative extinction.
• Test #2 - Droplet diameter of 4 mm, with support fiber and translation. Tethered deployment was successful with a brief burn before radiative extinction. Extinction occurred at “trailing surface ”after translation ceased.
• Test #3 - Droplet diameter of 4 mm, with no support fiber. Droplet deployment was successful with very little droplet drift. The burn was very brief before radiative extinction. The afterglow phenomena occurred again similar to Test #1.
• Test #4 - Droplet diameter of 4 mm, with support fiber and translation. Tethered deployment was successful with a brief burn before radiative extinction. A small amount of residual fuel from previous test was still on the fiber, which caused a brief secondary “ignition flash” that lasted less than 1 sec. Extinction occurred (similar to Test #2) at “trailing surface.”
Contacts at NASA Glenn Research Center