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

Papers:

• “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).

FLEX Status

February 2013:

•  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.)


February 2011: On February 9, 2011, the ISS crew replaced a CIR manifold bottle, and installed new fuel deployment needles and fiber arm assemblies.  Also, the combustion chamber window in front of the LLL-UV camera was replaced by the spare window from storage.  It was noted that the replaced window was smudged.  The source of the contamination is unknown, but appears to be consistent with contaminated fuel droplets.  Ground testing will be performed to determine the nature of the window contamination and determine if a cleaning procedure can be developed.  The replaced window was put into ISS storage.

The following is communication to the crew from Wednesday’s LIS summary.  (Do not put the LIS summary into the web site, however, the above can be put into the latest status block.)

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.

Paolo: Thank you for your excellent work replacing the window in the CIR's combustion chamber. We really appreciated the video camera views you gave us of the window as well as the photos.

Both your efforts have allowed us to get back to performing science! On GMT 045 - 046 we will calibrate the replaced hardware and perform test points

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. 


April 2010 - On-orbit operations continued for the Multi-use Droplet Combustion Apparatus’ Flame Extinguishment Experiment (MDCA/FLEX) this past week.  The depleted methanol fuel reservoir was replaced with another methanol reservoir on April 26, 2010.  The Molecular Sieve adsorber cartridge was replaced on April 27, 2010, with the Silica Gel adsorber cartridge.  The Molecular Sieve adsorber was installed for use with the nitrogen test points.

• 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.

Project Management:

Contacts at NASA Glenn Research Center

Project Manager: Mark Hickman, NASA GRC
john.m.hickman@nasa.gov
216-977-7105

Project Scientist: Dr. Daniel Dietrich, NASA GRC
daniel.l.dietrich@nasa.gov
216-433-8759

Principal Investigator Team: Prof. Forman Williams, UCSD (lead)
faw@ames.ucsd.edu
Prof. Frederick Dryer, Princeton
fldryer@princeton.edu
Prof. Mun Choi, Drexel University
choi@drexel.edu
Prof. Benjamin Shaw, UC-Davis
bdshaw@ucdavis.edu
Dr. Vedha Nayagam, NCSER
v.nayagam@grc.nasa.gov