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)
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
