Cool Flames Investigation (Cool Flames Investigation) - 03.13.19

Overview | Description | Applications | Operations | Results | Publications | Imagery

ISS Science for Everyone

Science Objectives for Everyone
Some types of fuels initially burn very hot, then appear to go out — but they continue burning at a much lower temperature, with no visible flames (cool flames). Understanding cool flame combustion helps scientists develop new engines and fuels that are more efficient and less harmful to the environment. The Cool Flames Investigation provides new insight into this phenomenon, as well as new data on fire safety in space.
Science Results for Everyone
Information Pending

The following content was provided by Daniel L. Dietrich, Ph.D., and is maintained in a database by the ISS Program Science Office.
Experiment Details


Principal Investigator(s)
Daniel L. Dietrich, Ph.D., Glenn Research Center, Cleveland, OH, United States
Forman A. Williams, Ph.D., University of California, San Diego, La Jolla, CA, United States

Frederick L. Dryer, Princeton University, Princeton, NJ, United States

NASA Glenn Research Center, Cleveland, OH, United States
ZIN Technologies Incorporated, Cleveland, OH, United States

Sponsoring Space Agency
National Aeronautics and Space Administration (NASA)

Sponsoring Organization
NASA - Space Life and Physical Sciences-Physical Sciences (NASA-SLPS-Physical Sciences)

Research Benefits
Earth Benefits, Scientific Discovery

ISS Expedition Duration
March 2016 - February 2018

Expeditions Assigned

Previous Missions
Information Pending

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Experiment Description

Research Overview

  • Understand  the low temperature combustion characteristics of normal alkanes by conducting droplet combustion experiments in low gravity in order to help combustion chemists develop new computational models to compute performance and efficiency for many practical applications on earth including high-efficiency Homogeneous Charge Compression Ignition (HCCI) engines
  • Investigate the low temperature burning behavior of droplets consisting of pure fuels, bio-fuels, and surrogate reference fuels to determine the relationship between the cool flame burning characteristics and the octane/cetane behavior of the fuel.
  • Explore the low temperature chemistry of alkanes further by mixing additives to the fuel that disrupt the low temperature chemical pathways.


In recent International Space Station (ISS) experiments (FLEX), a cool flame mode of burning was observed to develop after radiative extinction of a burning droplet. This result was not predicted by computational models (based on high temperature chemistry) nor expected based on prior experimental work. This unique burning behavior highlights the need to better understand both low and intermediate temperature fuel chemistry and its effect on droplet combustion, having implications for spray combustion and fire safety. This unexpected observation has attracted international interest from researchers in academia, industry, and government laboratories.
The Cool Flame Investigation (CFI) offers a unique opportunity to study the combustion of large alkane fuel droplets that exhibit hot ignition followed by radiative extinction and continued burning by low‐temperature combustion (cool flame chemistry) in the presence of heat loss. A basic understanding of cool flames is important for understanding ignition phenomena of practical fuels and fuel additives. Cool flames play a key role in the development and selection of new fuels and the design of advanced internal combustion engines.
The research also helps combustion chemists to develop new computational models to compute combustion performance in for many practical applications on earth, including an understanding of how cool flame reactivity determines octane and cetane number for fuels in spark ignition and diesel engines.

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Space Applications
This investigation studies the low-temperature burning behavior of several fuels (burned as droplets), including pure hydrocarbons, biofuels and mixtures of pure hydrocarbons. Results provide new understanding of low temperature chemistry, which benefits development of new engines and fuels and improves crew safety.

Earth Applications
Cool flame chemistry is important for developing fuels for advanced engines, such as high-efficiency Homogeneous Charge Compression Ignition engines. Results help combustion chemists design new computer models used to determine a fuel’s combustion performance. Next-generation fuels and engines produce less soot, improving air quality and benefiting people on Earth.

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Operational Requirements and Protocols

Droplets must be deployed free floating without any residual momentum in the center of the field of view of the CIR diagnostics. Diagnostics must be capable of recording the radiant emissions of both hot and cool flames. CIR must store be able to store digital imagery data from a full day of test point (approx. 8 burns) for later downlink.

Following setup and initialization of the CIR rack and MDCA, the chamber is filled with the appropriate atmosphere for the day’s test points. Conditions vary in pressure (0.5 atm to 5.0 atm) and oxygen concentration (10 to 30%). A settling time of approximately 2 minutes elapses prior to initiating the test in order to ensure that the temperature and pressure of the chamber gases have stabilized. This settling time is followed by the dispensing of a predetermined amount of fuel (based on the target droplet size) onto a support fiber. When sufficient fuel has been dispensed the dispensing needles are retracted and a dwell period of at least 10 seconds is allowed for the droplet internal fluid motion induced by deployment to subside. This is then be followed by initiating power to an igniter pair 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. A near real-time download of the color camera video is required in order to verify successful droplet deployment, ignition, and overall progress of the experiment. Pressure and temperature data of the chamber environment is also required in near real time.

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Decadal Survey Recommendations

Applied Physical Science in Space AP7
Applied Physical Science in Space AP8

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Results/More Information

Information Pending

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Results Publications

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Ground Based Results Publications

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ISS Patents

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Related Publications

    Nayagam V, Dietrich DL, Williams FA.  Partial-burning regime for quasi-steady droplet combustion supported by cool flames. AIAA Journal. 2016 January 11; epub: 5 pp. DOI: 10.2514/1.J054437.

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Related Websites
NASA Glenn Research Center: Cool Flames Investigation

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