NASA – Advanced Combustion via Microgravity Experiments yale university flag

The structure & liftoff in combustion experiment (SLICE) conducted in early 2012 (increment 30) was a precursor to ACME’s coflow laminar diffusion flame (CLD flame) experiment. ACME is also related to the smoke point in coflow experiment (SPICE) which was conducted in 2009 (and 2012 with SLICE), where SLICE and SPICE used the same experimental hardware within the microgravity science glovebox (MSG).

The advanced combustion via microgravity experiments (ACME) project includes five independent experiments investigating laminar gaseous non-premixed flames. In other words, the flow is smooth and without vortices, the fuel is a gas (and not a liquid or solid), and the fuel and oxygen are not mixed in the burner (but are instead on opposite sides of the flame sheet).

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, for example through the development and verification of improved computational models. A secondary objective is fire prevention, especially for spacecraft.

Some specific ACME goals are to improve our understanding of combustion at fuel lean conditions where both optimum performance and low emissions can be achieved, soot control and reduction, oxygen-enriched combustion which could enable practical carbon sequestration, flame stability and extinction limits, and the use of electric fields for combustion control.

The goal of ACME’s spacecraft fire prevention research is 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 the screening and selection of materials for spacecraft.

Coflow laminar diffusion flame (CLD flame): research, including that already 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. Yale university school colors the 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 diluted methane and ethylene flames in an air coflow. 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. The structure & liftoff in combustion experiment (SLICE) was conducted as a precursor to ACME’s CLD flame experiment, in order to maximize its science, e.G., through refinement of the test matrix.

Electric-field effects on laminar diffusion flames (E-FIELD flames): an electric field can strongly influence flames because of its effect on the ions produced by the combustion reactions. The direct ion transport and the induced ion wind can modify the flame shape, alter the soot or flammability limits, direct heat transfer, and reduce pollutant emission. The purpose of the electric-field effects on laminar diffusion flames (E-FIELD flames) experiment is to gain an improved understanding of flame ion production and investigate how the ions can be used to control non-premixed flames. Outside reviewers concluded that the experiment “has great prospects of improving our understanding of nearly every practical combustion device.” the experiment is conducted with a simple gas-jet flame, where an electric field is generated by creating a high voltage (up to 10 kv) differential between the burner and a flat circular mesh above (i.E., downstream of) the burner. Psychology yale university measurements are made of the ion current through the flame and the flame’s response to electric forcing as a function of the field strength, fuel, and fuel dilution.

Flame design: the primary goal of the flame design experiment is to improve our understanding of soot inception and control in order to enable the optimization of oxygen enriched combustion and the “design” of non-premixed flames that are both robust and soot free. An outside review panel declared that flame design “… could lead to greatly improved burner designs that are efficient and less polluting than current designs." flame design investigates the soot inception and extinction limits of spherical microgravity flames created with porous spherical burners. Tests are conducted with various concentrations of both the fuel (i.E., ethylene or methane) and oxygen in order to determine the role of the flame structure on the soot inception. The effect of the flow direction on soot formation is assessed by studying both normal flames and inverse flames, where in the latter case an oxygen/inert mixture flows from the spherical burner into a fuel/inert atmosphere. The flame design experiment explores whether the stoichiometric mixture fraction can characterize soot and flammability limits for non-premixed flames like the equivalence ratio serves as an indicator of those limits for premixed flames.

Structure and response of spherical flames (s-flame): the purpose of the structure and response of spherical flames (s-flame) experiment is to advance our ability to predict the structure and dynamics, including extinction, of both soot-free and sooty flames. The spherical flames are ignited at non-steady conditions and allowed to transition naturally toward extinction. Tests are conducted with various inert diluents, in both the fuel and chamber atmosphere. The fuel gases include hydrogen and methane mixtures for soot-free flames, and ethylene for sooty flames. One experiment objective is to identify the extinction limits for both radiative and convective extinction (i.E., at high and low system damköhler numbers, respectively). Another objective is to determine the existence, onset, and nature of pulsating instabilities that have been theoretically predicted to occur in such flames with fuel/diluent mixtures that are above a critical lewis number. ^ back to top

ACME’s BRE experiment is focused on spacecraft fire prevention. BRE’s objective is 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. The other four ACME experiments are not being conducted for space applications, but their results may be applicable to space applications such as waste processing or spacecraft fire safety.

With the exception of BRE, the ACME experiments are primarily focused on energy and environmental concerns. Yale medical college ACME’s primary objective is to gain fundamental understanding that can enable improved efficiency and reduced pollutant production in practical combustion processes on earth, for example through the development and verification of advanced computational simulations. In addition to enhanced performance, improved modeling capability can lead to reductions in the time and cost for combustor design. Some specific goals are to improve our understanding of combustion at fuel lean conditions where both optimum performance and low emissions can be achieved, soot control and reduction, oxygen-enriched combustion which could enable practical carbon sequestration, flame stability and extinction limits, and the use of electric fields for combustion control.