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Advanced Combustion Via Microgravity Experiments (ACME)




  • ACME is focused on advanced combustion technology via fundamental microgravity research.  The primary goal is to improve efficiency and reduce pollutant emission in practical terrestrial combustion.  A secondary objective is fire prevention, especially for spacecraft.

  • Currently, ACME includes five independent experiments (see ACME Experiments below) investigating laminar, gaseous, non-premixed flames.

  • The ACME experiments will be conducted with a single modular set of hardware (see ACME Implementation) in the Combustion Integrated Rack (CIR) on the International Space Station (ISS).

  • An ACME precursor, Structure & Liftoff In Combustion Experiment (SLICE), was conducted in the ISS’ Microgravity Science Glovebox (MSG) in early 2012.

  • The ACME design is complete and the engineering hardware is being assembled for integrated testing.  On-orbit testing is expected to begin in 2016 and continue for a few years.

  • ACME Status

    Awards and Recognitions:

    Best Thesis Award – Undergraduate student Laurel Paxton received the Morgan McKinzie Prize for the best senior thesis from Princeton’s Department of Mechanical and Aerospace Engineering. The thesis research, “Weakly buoyant spherical diffusion flames: properties of hydrogen-CO/ethylene flames,” is in support of the Structure and Response of Spherical Diffusion Flames (s-Flame) experiment which will be conducted on the International Space Station as part of the Advanced Combustion via Microgravity Experiments (ACME) project.  Her advisor, Prof. C.K. Law, is the s-Flame Principal Investigator.

  • April 2014 –Since Feb. 2013, over 30 tests have been conducted for the ACME project in the Zero Gravity Research Facility at the NASA Glenn Research Center (GRC). During this same period, over 200 ACME tests were conducted in NASA Glenn’s 2.2 Second Drop Tower, where much of that testing was carried out by NASA interns who were either undergraduate students or recent graduates. The drop tests were primarily conducted to evaluate (1) prototype burners fabricated by U. Maryland, Princeton U., and Yale U.; and (2) signal levels with flight-like instrumentation and cameras, e.g., in order to determine appropriate amplification and settings. The Requirements Definition Review (RDR) for the Burning Rate Emulator (BRE) experiment was held in June 2013, for which its Science Requirements Document (SRD) was updated. The BRE RDR was accompanied (on the next day) by a delta Preliminary Design Review (PDR) for ACME. In this regard, BRE was a late addition to ACME, where ACME’s RDR and PDR had been previously held (i.e., for the four initial experiments) in 2010 and 2011, respectively. The requirement changes from BRE’s RDR were fully incorporated into ACME’s Integrated Science Requirements Document (ISRD) in preparation for ACME’s Critical Design Review (CDR), which was held in November 2013. At this time, it is projected that ACME will operate on the International Space Station (ISS) from 2016 to 2019. Overviews of the ACME project were presented at the meetings of the American Society for Gravitational and Space Research (ASGSR) and the Central States Section of The Combustion Institute (CSS/CI) in November 2013 and March 2014, respectively. The paper and presentation for the latter conference are now available online.

  • ACME NUMBERS: 3, 5, 8, 11

  • 3 payload developers: ZIN Technologies, Inc., NASA, and the National Center for Space Exploration Research (NCSER).
  • 5 current ACME experiments (see below).
  • 8 universities with which ACME investigators have been affiliated, but where investigator Prof. Felix J. Weinberg of Imperial College London regrettably died in 2012.  There are also ACME investigators from the NASA Glenn Research Center, which is the agency’s lead for microgravity combustion research.
  • 11 current investigators for the ACME experiments.

  • ACME Logo

    ACME Experiments
    (listed alphabetically)

    Burning Rate Emulator (BRE)

    • Objective: Fire Safety- To improve our fundamental understanding of materials flammability, such as extinction behavior and the conditions needed for sustained combustion, and to assess the relevance of existing flammability test methods for low and partial-gravity environments.
    • Flame/Burner: Flat perforated disk fed with gaseous fuel to simulate the burning of solid and liquid fuels, where measurements are made of the thermal feedback upon which the vaporization of such fuels depend.
    • Principal InvestigatorProf. James G. Quintiere, University of Maryland
    • Co-Investigator: Prof. Peter B. Sunderland, University of Maryland

    Coflow Laminar Diffusion Flame (CLD Flame)

    • Objective: Energy & Environment - To extend the range of flame conditions that can be accurately predicted by computational models, especially for highly dilute and heavily sooting conditions.
    • Flame/Burner: Coflow flame where the gaseous fuel issues from an inner tube which is centered within a much larger outer tube, where a mixture of oxygen and nitrogen issues from the annulus.
    • Principal Investigator: Prof. Marshall B. Long, Yale University
    • Co-Investigator: Prof. Mitchell D. Smooke, Yale University

    Electric-Field Effects on Laminar Diffusion Flames (E-FIELD Flames)

    • Objective: Energy & Environment - To gain an improved understanding of ion production in flames and investigate how an electric field can be used to control flames through those ions.
    • Flame/Burner: Gas-jet flame, where (1) the gaseous fuel issues from a small circular tube into a still atmosphere, and (2) a high-voltage electric field is established between the burner and  disk-shaped copper mesh centered a few centimeters “above” the burner.  Electric-field tests may also be conducted with the coflow burner used for the CLD Flame experiment.
    • Principal Investigator: Prof. Derek Dunn-Rankin, University of California - Irvine

    Flame Design

    Structure and Response of Spherical Diffusion Flames (s-Flame)

    • Objective: Energy & Environment - To advance our ability to predict the structure and dynamics, including extinction, of both soot-free and sooty flames.
    • Flame/Burner: Spherical flame - which is only possible in microgravity - where the gaseous fuel (fed through a small tube) issues from a porous spherical burner into a still atmosphere.
    • Principal Investigator: Prof. C.K. Law, Princeton University
    • Co-Investigators: (1) Prof. Stephen D. Tse, Rutgers University; (2) Dr. Kurt R. Sacksteder, NASA Glenn Research Center


    Why study combustion?

    • In the United States, nearly 70% of our electrical energy is generated through the combustion of fossil fuels.  For example, in 2012, electricity was generated in the U.S. by burning the following fuels, where the percentages indicate the fraction of the total U.S. electrical generation: coal (37%), natural gas (30%), biomass (1.4%), and petroleum (1%).

    • Our transportation is heavily reliant on combustion, even for electric vehicles because most of our electricity is generated by combustion.

    • With combustion, we heat our homes, water, food, etc. and also generate heat for industrial processes.

    • Our reliance on imported fuel contributes to our national trade deficit and affects our national security.

    • Combustion is a leading man-made source of greenhouse gases, where carbon dioxide is the most important example.

    • Combustion is the primary man-made contributor to acid rain.

    • Soot contributes to global warming and is a health problem.

    • Fire safety!

    • Given our pervasive use of combustion as an energy source, the U.S. consumes fossil fuels which cost on the order of a trillion dollars annually.  Therefore, even small improvements in combustion efficiency would significantly reduce fuel needs and pollutant production.

    Why study combustion in microgravity?

    • Flames are strongly affected by gravity because the high-temperature combustion gases are much less dense than the cooler atmosphere which surrounds the flame.  Gravity pulls more forcefully on the denser atmosphere and the hot gases are pushed upward as a result.  This gravity-driven upward motion of material that is less dense that the surrounding fluid is referred to as buoyancy.  This gravity-driven motion, referred to as buoyant convection, feeds the flame with fresh reactant - normally oxygen (in the air) - and removes the combustion products (e.g., carbon dioxide and water vapor) from the flame vicinity.

    • Low-momentum flames are dramatically influenced by the effective elimination of buoyant convection, where the resulting effects are often advantageous for analysis. 

    • Spherically symmetric flames can be created enabling one-dimensional analysis.  Two of the current ACME experiments take advantage of this feature.

    • Flicker, which is a buoyancy-driven (i.e., gravity-driven) instability, is eliminated yielding quasi-steady flames.

    • 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.

    • Microgravity flames are great for studies of limit and stability behavior where chemical kinetics are important.  Soot, extinction, and stability limits are being studied in the ACME experiments.

    • Microgravity is of course the appropriate environment for studies related to spacecraft fire safety.

    Why study combustion on the ISS?

    • Microgravity durations in drop facilities, such as the 2.2 Second Drop Tower and 5.18-second Zero Gravity Research Facility, are (1) too short for soot to achieve quasi-steady conditions, and (2) too short to establish a flame and then vary its flow rate, for example, to investigate stability or extinction limits.
    • While research aircraft flying in parabolic maneuvers can provide reduced gravity durations of ~20 seconds, low-momentum flames are often dramatically disturbed by the aircraft vibrations.  Although the jitter can be avoided if the experiment is floated within the aircraft, that reduces the low-gravity duration to mere seconds.
    • Space-based testing is often necessary to achieve microgravity conditions of sufficient duration and quality for combustion research.


    Past News & Status


    C2H4 Flames

    Feb. 2013 – Preparations are underway to conduct evaluation tests for the Burning Rate Emulator (BRE) experiment in NASA Glenn’s Zero Gravity Research Facility using a prototype burner developed by the University of Maryland investigators, Profs. Jim Quintiere and Peter Sunderland.  This follows forty exploratory tests that were conducted with a similar gas-fueled burner in November 2012 in NASA Glenn’s 2.2 Second Drop Tower.  In each drop facility, apparent weightlessness is momentarily achieved by letting the self-contained experiment freely fall down a vertical shaft.  The November tests were conducted in ambient air and sometimes revealed lifting phenomena and possible tip quenching when the fuel was methane or diluted methane.  Meanwhile, the ethylene flames remained robust throughout the 2.2-second test duration.  The “cup” burner used in the November tests was equipped with a heater, where its use had a significant effect on the ethylene flame as can be seen in the sample images below.

    October 2012 – Detailed design is underway, where ACME passed an interim design review in June.  A successful Science Concept Review was held for the Burning Rate Emulator (BRE) experiment in August, where the external reviewers concluded that BRE “may offer critical guidance in flammability assessment in space vehicles.”  The Requirements Definition Review for BRE and the Critical Design Review for ACME are planned for June and November 2013, respectively.  The extra reviews are necessary for BRE because it wasn’t originally an ACME experiment and its design isn’t yet fully specified.  It is currently expected that ACME will begin testing on ISS in 2016.

    April 2012 – Tests were recently completed on the International Space Station for the Structure & Liftoff In Combustion Experiment (SLICE) which is a precursor to ACME’s Coflow Laminar Diffusion Flame (CLD Flame) experiment.  The SLICE results will enable refinement of the CLD Flame test matrix and operating procedures so as to maximize its scientific outcome.  You can learn more about SLICE at its Facebook page.

    January 2012 – A fifth experiment was added to the ACME project, Burning Rate Emulator (BRE), where the investigators are Profs. J.G. Quintiere and P.B. Sunderland of the University of Maryland.  BRE’s objective is to improve our fundamental understanding of materials flammability and assess the relevance of existing flammability test methods for low and partial-gravity environments.  The burning of solid and liquid fuels will be simulated using a flat porous burner, where the flow rate of gaseous fuel will be controlled based on the thermal feedback to the burner.

    January 2011 - The Advanced Combustion via Microgravity Experiments (ACME) Preliminary Design Review (PDR) was held on January 28, 2011.  The Project team demonstrated that the preliminary design meets all system requirements with acceptable risk and within cost and schedule constraints.  The review board has recommended that the project proceed with detailed design.

    May 2010 - The Advanced Combustion via Microgravity Experiments (ACME) Requirements Definition Review (RDR) was held for two days, May 10-11, 2010  The Science Requirements Document (SRD) was signed by all parties except for one PI who had to leave early before the signature page was prepared.

    August 2009 -
     The ACME project is conducting drop tower testing at the Glenn Research Center’s 2.2 second drop tower with the ACME E-Fields rig.  The drop tower tests are focusing on the high voltage field effects on flames, these tests were conducted during the month of July 2009 by the project scientist and summer intern.