Advanced Combustion via Microgravity Experiments

The Advanced Combustion via MicrogravityThe condition of perceived weightlessness created when an object is in free fall, for example when an object is in orbital motion. Microgravity alters many observable phenomena within the physical and life sciences, allowing scientists to study things in ways not possible on Earth. The International Space Station provides access to a persistent microgravity environment. Experiments (ACME) project is a set of six independent studies of gaseous flames to be conducted in the Combustion Integrated Rack (CIR). ACME investigates 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 emissions in practical terrestrial combustion; for example, through the development and verification of improved computational models. A secondary objective is fire prevention, especially for spacecraft. In addition to enhanced performance, the improved modeling capability resulting from ACME could lead to reductions in the time and cost for combustor design. Some specific ACME goals are to improve understanding of combustion at lean fuel 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 the 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.

The ACME chamber insert currently has a retractable igniter and four different burners that can be installed one at a time. These include a co-flow burner, a gas jet burner, a flat porous burner (burning rate emulator), and a porous spherical burner. For diagnostics, the ACME chamber insert has several thermocouples for temperature, several radiometers for radiant emission, mass flow controllers for gas flow rates, color video and imaging, OH* imaging, light extinction measurements via a High-Bit Depth Multispectral camera (HiBMs), chemiluminescent measurements via photomultiplier tubes, and gas chromatography.