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).
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.
Below is an example of a combustion event
using heptane liquid fuel. This video is imaged with a standard
NTSC color camera and is essentially what you would see
if you were looking through a window in the CIR chamber.
The fuel droplet is suspended on thin Silicon Carbide (SiC)
fiber. The primary function of the fiber in this test
is simply to pin the burning droplet to a fixed location.
The initial frame shows the fuel droplet suspended on the
fiber and surrounded by two hot wire igniters and the fuel
dispensing needles. This is taken with the CIR chamber light
on. The light is off for the remainder of the video. At
about 1 second into the clip, the igniters are powered and
the droplet ignites saturating the camera image. The
igniters can been as they retract from the ignition site.
Afterward the combustion event can be observed as a thin
bluish shell surrounding the liquid droplet. The fiber
is heated and glows at the two points where it intersections
with the flame shell. At approximately 8-9 seconds
the flame extinguishes due to radiative heat loss and the
fiber cools below the camera’s color range. The
flames shell collapses and the light from the flame diminishes,
however the remaining liquid is still illuminated by the
CIR laser backlight (partially visible at the lower portion
of the image). All of the above is representative
of the primary FLEX science investigation.
Then we have some unexplained phenomena. Over the next 12-15
seconds the fuel droplet is observed to exhibit a sustained
rapid evaporation as if some reaction is still active. (This
is more easily observed with the associated HiBMs camera
images – not included here). At the end of this
phase we observe the remaining fuel droplet as it oscillates
back and forth on the fiber. At about the 25 seconds the
rapid evaporation ceases and the vapor atmosphere begins
to condense into a toroidal cloud shape. As
the system cools the image appears to brighten to a deep
red as the vapor continues to condense and increase in density.
The post combustion vaporization was not predicted by existing
science and is of great interest to the community. Currently,
there is no clear understanding of the cause/process
driving the post-extinction vaporization, nor is it understood
whether the cloud formation consists of water, fuel or a
mixture of both. The phenomenon is repeatable. Should
the cloud contain condensed fuel it represents a potential
ignition hazard in micro-gravity environments even after
nominal extinction occurs.
Communication clip from the intro
about CIR (Mike Fossum on
9/22/2011)
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.
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.
Below is a selection of FLEX Test Point
videos.
• 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.”
Multi-user Droplet Combustion
Apparatus (MDCA)
Color image of a burning
droplet
FLEX Chamber Insert Assembly
Apparatus
Flight Unit Avionics Package
installed on Ground Unit Optics Bench Simulator and Flight Unit
Chamber Insert Assembly.
Flight Unit Chamber Insert
Assembly
Flight Unit Avionics Package
installed on Ground Unit Optics Bench Simulator
Flight Unit Avionics Package
installed on Ground Unit Optics Bench Simulator
The Multi-user Droplet Combustion Apparatus (MDCA) is a multi-user facility
designed to accommodate different droplet combustion science experiments. The
MDCA will conduct experiments using the Combustion Integrated Rack
(CIR) of the NASA Glenn Research Center’s Fluids and Combustion
Facility (FCF). The payload is planned for the International
Space Station. The MDCA, in conjunction with the CIR, will
allow for cost effective extended access to the microgravity environment,
not possible on previous space flights. It is currently in
the Engineering Model build phase with a planned flight launch with
CIR in 2007.
The MDCA contains the hardware and software required
to conduct unique droplet combustion experiments in space. It
consists of a Chamber Insert Assembly (CIA), an Avionics Package,
and a multiple array of diagnostics. Its modular approach permits
on-orbit changes for accommodating different fuels, fuel flow rates,
soot sampling mechanisms, and varying droplet support and translation
mechanisms to accommodate multiple investigations. Unique diagnostic
measurement capabilities for each investigation are also provided. Additional
hardware provided by the CIR facility includes the structural support,
a combustion chamber, utilities for the avionics and diagnostic packages,
and the fuel mixing capability for PI specific combustion chamber
environments. Common diagnostics provided by the CIR will also
be utilized by the MDCA. Single combustible fuel droplets of
varying sizes, freely deployed or supported by a tether are planned
for study using the MDCA. Such research supports how liquid-fuel-droplets
ignite, spread, and extinguish under quiescent microgravity conditions. This
understanding will help us develop more efficient energy production
and propulsion systems on Earth and in space, deal better with combustion
generated pollution, and address fire hazards associated with using
liquid combustibles on Earth and inspace.
As a result of the concurrent design process of MDCA
and CIR, the MDCA team continues to work closely with the CIR team,
developing Integration Agreements and an Interface Control Document
during preliminary integration activities. Integrated testing
of hardware and software systems will occur at the Engineering Model
and Flight Model phases. Because the engineering model is a
high fidelity unit, it will be upgraded to a flight equivalent Ground
Integration Unit (GIU) when the engineering model phase is completed. The
GIU will be available on the ground for troubleshooting of any on-orbit
problems. Integrated verification testing will be conducted
with the MDCA flight unit and the CIR flight unit. Upon successful
testing, the MDCA will be shipped to the Kennedy Space Center for
a post-shipment checkout and final turn-over to CIR for final processing
and launch to the International Space Station.
Once on-orbit, the MDCA is managed from the GRC Telescience
Support Center (TSC). The MDCA operations team resides at the
TSC. Data is transmitted to the PI’s at their home sites
by means of TREK workstations, allowing direct interaction between
the PI and operations staff to maximum science. Upon completion
of a PI’s experiment, the MDCA is reconfigured for the next
of the three follow-on experiments or ultimately removed from the
CIR, placed into stowage, and returned to Earth.
MDCA/CIR Testing and Integration
Integrated testing between the MDCA hardware
and CIR carrier will be performed on the engineering units of both
pieces of hardware. Both units are hi-fidelity, flight-like
units. Testing, planned for December 2002 will include a full
array of sub-package testing, leading to a full end-to-end functional
test. Upon completion, the MDCA Engineering Model (EM) will
undergo vibration & microgravity testing, EMI/EMC, and acoustical
testing. In parallel with EM environmental testing, the MDCA
flight hardware will be procured and assembled. Testing will
be conducted on the flight unit in early summer 2005 in preparation
for a turn-over of the hardware to CIR for flight integrated testing
in August 2005.
Launch of the MDCA Hardware
The MDCA hardware will be launch as stowed hardware
on the same incremental flight launch as the CIR. This hardware
will include the MDCA common hardware and experiment unique hardware
for the first droplet investigation, Flame Extinguishment Experiment
(FLEX). The Chamber Insert Assembly, MDCA Avionics Package,
and experiment unique hardware will be separate stowed items. Once
on-orbit, the CIA and Avionics Package will be removed from stowage. The
avionics package will be installed on the CIR rack and the CIA will
be inserted into the CIR combustion chamber. Experiment unique
diagnostics for the first experiment will be installed on the CIR
optics bench.
Contacts at NASA Glenn Research Center Project Manager: Mark Hickman, NASA
GRC john.m.hickman@nasa.gov
216-977-7105
