Coflow Laminar Diffusion Flame (CLD Flame) - 11.29.18

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Science Objectives for Everyone
The Coflow Laminar Diffusion Flame (CLD Flame) experiment is conducted in the Combustion Integrated Rack (CIR) on the International Space Station, as part of the Advanced Combustion via Microgravity Experiments (ACME) project. In this experiment, the flame - burning a gaseous fuel - is surrounded by air flowing in the same direction. Measurements are made of flame characteristics such as the size, structure, temperature, soot, and stability. Conducting the tests in microgravity allows for great simplifications in the analysis, enabling new understanding and the development of more efficient and less polluting combustion technology for use on Earth.
Science Results for Everyone
Information Pending

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


Principal Investigator(s)
Marshall Long, Ph.D., Yale University, New Haven, CT, United States

Mitchell D. Smooke, Ph.D., Yale University, New Haven, CT, United States
Sergey Minaev, Ph.D., Far Eastern Federal University, Vladivostok, Russia

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 Research Office - Space Life and Physical Sciences (NASA Research-SLPS)

Research Benefits
Earth Benefits, Scientific Discovery

ISS Expedition Duration
September 2017 - October 2018

Expeditions Assigned

Previous Missions
Information Pending

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Experiment Description

Research Overview

  • The overall goal of the Coflow Laminar Diffusion Flame (CLD Flame) investigation is to improve our understanding of the physical and chemical processes controlling diffusion (i.e., non-premixed) flame structure and lifting phenomena (i.e., stabilization) and to provide for rigorous testing of numerical models, including thermal radiation, soot formation, and detailed chemical kinetics. Such understanding allows for detailed computational predictions, e.g., of pollutant formation, and enables the improvement of combustion efficiency and reduction of pollutant emission in practical terrestrial combustion.
  • Microgravity studies of flames allow for a range of simplifications and provide various advantages over normal-gravity studies. For example, the flicker of flame, which is a buoyancy-driven (i.e., gravity-driven) instability, is eliminated yielding quasi-steady flames in microgravity. Length scales are increased in microgravity flames facilitating analysis of the flame structure. Momentum-dominated flames, which are important for most practical combustion, can be studied at low velocities to simplify analysis. Microgravity flames tend to have a much stronger sensitivity to their atmosphere and exhibit a much broader range of characteristics than normal-gravity flames because of the near absence of buoyant entrainment. The long residence times in microgravity flames can lead to strong soot production, but many microgravity flames are soot free. The absence of buoyancy makes microgravity flames advantageous for studies of limit and stability behavior where chemical kinetics are important. With these advantages, microgravity testing can lead to new understanding of the complex nature of combustion – regardless of the gravitational environment of the combustion application.
  • A coflow flame can be created where gaseous fuel flows from an inner tube which is centered within a much larger outer tube, where a mixture of oxygen and inert gas (e.g., nitrogen) flows from the annulus. Diffusion flames of methane and ethylene, with various nitrogen dilutions, burning in a coflow of air are studied.
  • The Coflow Laminar Diffusion Flame (CLD Flame) experiment characterizes the structure of the flame, especially its base (i.e., stabilizing region), from attached through lifted conditions as a function of the fuel (including nitrogen dilution) and flow conditions. The velocity limits where the flame detaches from the burner and later extinguishes are similarly identified as a function of the fuel.
  • An understanding of lifting and lifted behavior is valuable, because of the importance of flame stability to the safe operation of practical combustion systems.

Research conducted in microgravity has revealed that our current predictive ability is significantly lacking for flames at the extremes of fuel dilution, namely for sooty pure-fuel flames and dilute flames that are near extinction. The general goal of the Coflow Laminar Diffusion Flame (CLD Flame) experiment is to extend the range of flame conditions that can be accurately predicted by developing and experimentally verifying chemical kinetic and soot formation submodels. The dependence of normal coflow flames on injection velocity and fuel dilution is carefully examined for flames at both very dilute and highly sooting conditions. Measurements are made of the structure of methane and ethylene flames in an air coflow, where the fuels are often diluted with nitrogen. Lifted flames are used as the basis for the research to avoid flame dependence on heat loss to the burner. The results of this experiment are directly applicable to practical combustion issues such as turbulent combustion, ignition, flame stability, and more.

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Space Applications
The CLD Flame research is not being conducted to serve any space applications, but it is possible that its findings could aid the development of future space-based combustion devices (e.g., for solid waste processing).

Earth Applications
The combustion of fossil fuels is humanity’s primary source of energy and is used to produce electricity and for heating, transportation, and more. But it is also the primary human source of greenhouse gas and acid rain. Innovative combustion research conducted on the space station can yield new understanding of the intricacies of combustion enabling improved efficiency and reduced pollutant emission in practical combustion on Earth. Furthermore, improved design capability can enable reduced time and cost in the development of new furnaces and engines.

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Operational Requirements and Protocols
Coflow Laminar Diffusion (CLD) Flame experiments are configured, but not conducted, by the International Space Station (ISS) crew. The crew’s role is to set up the hardware, gas bottles, etc. for each set of tests. The most common changes include the gas bottles on the Combustion Integrated Rack (CIR) and the mass flow controllers on the modular ACME chamber insert. All testing is commanded from the ground, specifically from the Glenn ISS Payload Operations Center (GIPOC). The science portion of the testing is typically conducted in a nominally automated mode using pre-programmed scripts. However, it may alternately be conducted in a ‘manual’ mode, where changes are made to a control parameter in response to the analog video downlink and the numerical data available in the telemetry stream. For example, gas flow rate(s) can be adjusted to approach a flame’s stability or soot limit. Testing must not be conducted when thrusters fire or spacecraft dock or undock from ISS to ensure an acceptable acceleration environment. Data are downlinked between each set of tests, i.e., day of testing, to allow for preliminary analysis and requisite planning for subsequent testing.

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Decadal Survey Recommendations

Information Pending

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Results/More Information

Information Pending

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Related Websites
Combustion - Yale University
ZIN Technologies, Inc.
Yale Engineering 2012 – cover story on CLD Flame research (pp. 4, 24-29)
Coflow Laminar Diffusion Flame (CLD Flame) Experiment – Operations Center Site
Advanced Combustion via Microgravity Experiments (ACME) – NASA Glenn Research Center
Coflow Laminar Diffusion Flame (CLD Flame) Experiment – NASA Glenn Research Center
Space Flames – social media site for news, etc. on ACME and related research

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