Multi-User Droplet Combustion Apparatus Flame Extinguishment Experiment (MDCA-FLEX) will assess the effectiveness of fire suppressants in microgravity and quantify the effect of different possible crew exploration atmospheres on fire suppression. The goal of this research is to provide definition and direction for large scale fire suppression tests and selection of the fire suppressant for next generation crew exploration vehicles

Choi, Mun Y.

Dryer, Frederick L.

Nayagam, Vedha

Shaw, Benjamin D.

Williams, Forman A.

NASA Technical Reports Server

Acronym: MDCA-FLEX 
 
Title: Multi-User Droplet Combustion Apparatus - Flame Extinguishment Experiment  
 
Principal Investigator(s):  
Forman A. Williams, University of California, San Diego, San Diego, CA  
 
Co-Investigator(s)\Collaborator(s):  
Vedha Nayagam, National Center for Space Exploration Research, Cleveland, OH  
Mun Y. Choi, Drexel University, Philadelphia, PA  
Frederick L. Dryer, Princeton University, Princeton, NJ  
Benjamin D. Shaw, University of California, Davis, Davis, CA  
 
Contact(s):  
PI - Forman Williams, (858) 534-5492 
Primary - Michael Hicks, 216-433-6576 
Secondary - Vedha Nayagam, 216-433-8702 
 
Mailing Address(es): 
Developer(s): Glenn Research Center, Cleveland, OH 
ZIN Technologies, Cleveland, OH  
Sponsoring Agency: National Aeronautics and Space Administration (NASA) 
 
Increment(s) Assigned: 18, 19, 20  
 
Brief Research Summary (PAO): Multi-User Droplet Combustion Apparatus Flame Extinguishment 
Experiment (MDCA-FLEX) will assess the effectiveness of fire suppressants in microgravity and quantify 
the effect of different possible crew exploration atmospheres on fire suppression. The goal of this 
research is to provide definition and direction for large scale fire suppression tests and selection of the fire 
suppressant for next generation crew exploration vehicles.  
Research Summary:  
• The combustion and extinction characteristics of liquid fuel droplets in microgravity are 
determined by the complex interaction of fuel vapor and oxidizer transport, fuel vaporization, 
conductive, convective and radiative heat loss and chemical kinetics. All of these phenomena are 
critical in real fire scenarios and thus in understanding the complex issues involved in the design 
of an effective fire suppression system. 
• The simplicity of the droplet geometry lends itself to detailed theoretical and numerical studies. By 
comparing the results of the experiments to these detailed treatments it is possible to develop 
validated chemical kinetic and heat and mass transport mechanisms for liquid fuels. From these 
fundamental mechanisms it becomes possible to develop validated, predictive, reduced-scale 
mechanisms that are appropriate for modeling real fire suppression scenarios aboard future 
spacecraft. 
• The Multi-User Droplet Combustion Apparatus - Flame Extinguishment Experiment (MDCA-
FLEX) investigation will yield both a quantitative measure of the effectiveness of various 
suppression agents and more importantly a set of predictive tools that will allow the effective, 
efficient design of future spacecraft fire suppression systems. 
Detailed Research Description: Multi-User Droplet Combustion Apparatus - Flame Extinguishment 
Experiment (MDCA-FLEX) will map the flammability boundaries for liquid fuel combustion in reduced 
gravity to quantify the suppressant efficacy of various gaseous suppressants over the range of candidate 
https://ntrs.nasa.gov/search.jsp?R=20090014812 2019-08-30T06:35:43+00:00Z
atmospheric pressures and oxygen concentrations. This investigation will develop predictive theoretical 
and numerical codes and chemical kinetic schemes to model flammability boundaries as a function 
effective gravitational acceleration on the unique ambient conditions encountered in space exploration 
applications.The development and validation of these models will require detailed spatially and temporally 
resolved measurements of droplet burning rate, flame extinction, flame radiation, soot concentration, soot 
temperature, etc. This investigation will also develop improved and validated reduced (simplified) 
theoretical and numerical sub-models of important physical processes (chemical kinetics, radiation, soot 
formation/destruction) that can be used in simulations of large scale, realistic fires. 
 
The independent experiment variables analyzed by MDCA-FLEX are: 
 
Oxygen Mole Fraction: The ambient oxygen mole fraction in a typical space environment can vary from 
high concentrations in EVA pre-breathing environments down to that typically found in air. At high oxygen 
concentrations, however, the chemical times are small enough (relative to the characteristic flow times) 
such that the droplets will burn to completion rather than exhibiting flame extinction. Therefore, it is also 
necessary to study low oxygen concentrations, down to the Limiting Oxygen Index (LOI). It is also 
important to determine the LOI in order to verify the chemical mechanisms. The oxygen mole fractions in 
the present study will vary from 0.10 to 0.50. The chamber must also be large enough such that there is 
no significant decrease in ambient oxygen mole fraction during an experiment (i.e. the droplet burns in an 
essentially constant ambient). 
 
Diluent (non-suppressant): The ambient mixture will consist of oxygen mixed with a suppressant and 
the balance of an inert diluent gas. The diluent gas for these studies will be primarily nitrogen since that is 
the typical diluent on Earth and expected in space. There will be a small number of tests with a helium 
diluent gas. The reason is primarily for baseline comparisons with the Droplet Combustion Experiment, 
which used helium as the diluent gas and also to vary the physical properties of the diluent gas.  
 
Suppressant Type: The tests will examine candidate gaseous suppressants that have widely varying 
physical, chemical and radiative properties. This will enable model and sub-model development and 
validation over a wide range of ambient conditions to improve the predictive capabilities of the models. 
The suppressants are carbon dioxide and helium. The expected concentrations range from 0.00 mole 
fraction to the limit where no flame can exist (0.70 expected for the least active suppressant).  
 
Pressure: Ambient pressure does not significantly influence the droplet burning rate, but does influence 
chemistry at sufficiently low values. In addition, one strategy for extinguishing a fire is to isolate the 
habitat where it exists and vent the cabin to space. It is therefore beneficial to have verified suppressant 
data at low pressures. The pressure for the tests will range from 0.5 to 1.0 atm (standard atmosphere). As 
with the oxygen mole fraction, it is important that the test chamber be sufficiently large so that the 
pressure is essentially constant during an experiment (i.e. the droplet burns in a constant pressure 
ambient).  
 
Fuel Type: The advantage of the droplet geometry is that the fuel is relatively simple and better 
characterized than typical fuels in fire safety studies (e.g. PMMA or paper). This is also a disadvantage 
since it does not represent a practical fuel. The study will use two typical hydrocarbon fuels, an alcohol, 
methanol (CH3OH ) and an alkane, heptane (C7H16 ). There is a relatively large experience base with 
these fuels. Methanol has a fuel-bound oxygen atom, and burns with a very dim blue flame (not much 
soot production) with a small standoff distance, so it has widely different radiative characteristics than 
heptane. Therefore, studying these two fuels gives a wide range of fire scenarios to verify model and sub-
model performance over.  
 
Droplet Diameter: The droplet is ignited in the flammable region and then burns in a constant oxygen 
mole fraction ambient until flame extinction. Under the assumption of quasisteady burning, the initial 
droplet size should not significantly influence the determination of the extinction droplet size. Transient 
influences, however, will be present, so some variation in initial droplet diameter is necessary to 
determine the deviation from quasi-steady behavior. The initial droplet size in the proposed study will vary 
between 2 and 5 mm.  
Project Type: Payload  
Images and Captions: 
 
Burning droplet from the Droplet Combustion Experiment, image courtesy or Glenn Research Center.  
 
 
NASA Image: C-2006-414: Flight Unit Multi-User droplet Combustion Apparatus (MDCA) Chamber Insert 
Assembly (CIA).  
 
 
NASA Image: ISS018E010645 - Astronaut Michael Fincke, Expedition 18 commander, works on the 
Multi-User Droplet Combustion Apparatus (MDCA) Chamber Insert Assembly (CIA) in the Harmony node 
of the International Space Station.  
 
Operations Location: ISS Inflight  
Brief Research Operations:  
• MDCA-FLEX will be setup and operated in the Combustion Integrated rack (CIR) on ISS. 
• The investigation will generate droplets from methanol or heptane as required by the test point. 
• The data will be recorded via video using the CIR optics bench. 
Operational Requirements: The MDCA-FLEX investigation will be setup in the Combustion Integrated 
Rack (CIR). The CIR chamber will be filled with the appropriate atmosphere depending on the test point. 
A total of 196 test points are required for completion of MDCA-FLEX. Fuel will be dispensed followed by 
ignition. All activities will be captured in near real-time download with the CIR color camera video.  
Operational Protocols: Following setup and initialization of the MDCA-FLEX investigation the chamber 
shall be filled with the appropriate atmosphere, which depending on the test point, will vary in pressure 
from 0.5 atm to 3.0 atm, will vary in oxygen concentration from 0.1 to 0.4 mole fraction, and will vary in 
suppressant concentration from 0 to 0.7 mole fraction. A settling time of approximately 2 minutes will 
elapse prior to initiating the test in order to ensure that the temperature and pressure of the chamber 
gases have stabilized. This settling time will be followed by the dispensing of a predetermined amount of 
fuel (based on the target droplet size) onto the support fiber. When sufficient fuel has been dispensed the 
dispensing needles will be retracted and a dwell period of at least 10 seconds will be allowed for the 
droplet internal fluid motion induced by deployment to subside. 
 
This will then be followed by initiating power to the igniter for a selectable amount of time ranging from 1 
second to 5 seconds after which the igniter will be retracted from the field of view. If the flow field is to be 
generated by translating the droplet then droplet motion would commence at the same time that the 
igniter is retracted. A near real-time download of the color camera video will be required in order to verify 
successful droplet deployment, ignition, and overall progress of the experiment. Pressure and 
temperature data of the chamber environment will also be required in near real time. 
 
At least 2 minutes must be allowed after filling chamber to ensure that the chamber gas temperature and 
pressure has stabilized. For droplet dwell time allow at least 10 seconds to ensure all droplet motion 
imparted by droplet deployment and needle retraction has subsided. Chamber purity for fuel vapor mole 
fraction of less than 0.005 in the atmosphere for tests without carbon dioxide and less than 0.02 mole 
fraction (each species) of carbon monoxide, carbon dioxide and other products.  
Review Cycle Status: PI Reviewed  
Category: Technology Development  
Sub-Category: Spacecraft Systems  
Space Applications: MDCA-FLEX will help us develop more efficient energy production and propulsion 
systems on Earth and in space.  
Earth Applications: MDCA-FLEX will help in the understanding to deal better with combustion generated 
pollution, and address fire hazards associated with using liquid combustibles on Earth.  
Manifest Status: New  
Supporting Organization: Exploration Systems Mission Directorate (ESMD)  
Previous Missions: The Fiber Supported Droplet Combustion Experiment, (FSDC), a predecessor to 
MDCA-FLEX was performed on STS-73 (October 20, 1995) and STS-83 (April 4, 1997). The Droplet 
Combustion Experiment (DCE), another predecessor was performed on STS-83 (April 4, 1997) and STS-
94 (July 1, 1997). The fundamentals addressed by these experiments are essential to the fundamentals 
that impact fire sensing and suppression technologies applicable to space exploration environments.  
 
Web Sites: 
Space Flight Systems at GRC 
Last Update: 02/23/2009  
 


Multi-User Droplet Combustion Apparatus - Flame Extinguishment Experiment

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